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Pool Season Length by City: Swim Season Index for 60 US Metros (NOAA 1991-2020 Normals)

An index of outdoor swim-season length for the 60 largest US metro areas, counting the days each year when the 1991-2020 normal daily high at the main airport reaches 75F, 80F or 85F.
By PC&S Research Desk · Published October 4, 2026 · Data and tables licensed CC BY 4.0
Pool Season Length by City: Swim Season Index for 60 US Metros (NOAA 1991-2020 Normals)
The headline

Pool season length by city ranges from 0 to 365 days across the 60 largest US metros, measured as days when the 1991-2020 normal daily high reaches 80F. Honolulu qualifies year-round, Miami has 265 days and Phoenix 232, while Buffalo has 29. The population-weighted average is 113.5 days.

113.5 days
Population-weighted swim season across the 60 largest US metros: days per year with a 1991-2020 normal daily high of 80F or more (2025 population weights)
Source: PC&S analysis of NOAA NCEI normals and Census Vintage 2025
265 days
Miami (Miami International Airport), the longest season in the contiguous US at 80F, Mar 8 to Nov 27; Honolulu qualifies all 365 days (1991-2020 normals)
Source: NOAA NCEI
151.2 vs 81.4 days
Population-weighted 80F season in 28 Sun Belt metros (station south of 37N) vs 32 other large US metros, 1991-2020 normals
Source: PC&S analysis of NOAA NCEI normals and Census Vintage 2025
75.9%
Share of 2020 to 2025 population growth in the 60 largest US metros that went to the 28 Sun Belt metros
Source: U.S. Census Bureau Vintage 2025

How the index is built

  1. Ranked all 387 metropolitan statistical areas by July 1, 2025 population (Census Vintage 2025, cbsa-est2025-alldata.csv) and kept the top 60.
  2. Assigned each metro its main commercial airport station and confirmed every GHCN station ID in NCEI’s 1991-2020 normals inventory (inventory_30yr.txt).
  3. Downloaded NCEI 1991-2020 daily, monthly and annual/seasonal normals files (v1.0.1) for the 60 primary stations and 10 alternate stations.
  4. Dropped February 29 and counted days with DLY-TMAX-NORMAL at or above 75F, 80F and 85F; recorded the first and last day of the longest unbroken run.
  5. Computed the Swim Season Index (80F days / 365 x 100), population-weighted averages (2025 and 2020 weights), Sun Belt vs rest groups and Spearman correlation with latitude.
  6. Compared each metro with DOE’s 2016 state pool pump operating windows (DPPP TSD Table 7.3.11).
  7. Counted observed 2025 days at or above 80F for 7 stations from GHCN-Daily and compared them with NCEI’s ANN-TMAX-AVGNDS-GRTH080 average.

Included: Official NOAA NCEI normals and GHCN-Daily data, Census Bureau population estimates, federal rulemaking documents, NWS safety pages, and published guidance from the American Red Cross and World Aquatics.

Excluded: Pool water temperature (no national station dataset), social media and forum answers, unsourced ‘best time to open your pool’ claims, and any extrapolation beyond the 1991-2020 normals.

Conflicting numbers: Where the normal-curve count and NCEI’s observed-day average differ, both are shown and labelled. DOE season windows are shown as a separate assumption and never blended with climate counts. Where alternate stations in one metro disagree, the primary airport is used and the alternates are listed.

Derived metrics: All counts, dates, averages and comparisons come from scripts/build_index.py, scripts/derived_stats.py and scripts/make_facts.py run on the raw files in raw/; each result is a row in derived.csv.

Caveats

  • Air temperature is a proxy; pool water lags air temperature and depends on heating, covers and sun.
  • One airport station per metro cannot represent large or coastal metros; Los Angeles, San Diego and New York vary materially by station.
  • Daily normals are smoothed 30-year curves; they describe typical conditions, not any given year.
  • The Sun Belt latitude line is a PC&S proxy, not an official definition.
  • DOE operating windows are modelling assumptions from 2016, not observed pool use.
  • The 2025 comparison covers 7 stations for one year.

Method last reviewed October 4, 2026.

How pool season length by city is measured in this index

The index counts calendar days when the 1991-2020 normal daily high temperature at each metro’s main airport is at or above a threshold. The primary threshold is 80F, tested against 75F and 85F, and the Swim Season Index expresses the 80F count as a share of the year.

Metro selection: the 60 largest metropolitan statistical areas by July 1, 2025 population in the Census Bureau’s Vintage 2025 estimates, which cover 387 metro areas (U.S. Census Bureau). The 60 metros held 198,927,698 residents on July 1, 2025.

Climate data: each metro is represented by one primary commercial airport station from NOAA NCEI’s 1991-2020 U.S. Climate Normals, version 1.0.1 (NOAA NCEI). Station IDs are listed in every table. NCEI computes daily maximum temperature normals with a constrained harmonic least squares fit that gives precedence to monthly values (NOAA NCEI methodology), so each daily normal is a smoothed point on the typical annual curve, not an observed day.

Why 80F: air temperature is the only variable NOAA normals provide for every station, so the index uses the daily high as a proxy for outdoor swimming weather. The National Weather Service notes that sudden immersion can trigger gasping in water as warm as 77F (NWS). The NWS Baltimore/Washington office describes 70F to 78F water as the range where most people feel comfortable swimming (NWS). World Aquatics sets competition pool water at 25C to 28C, which is 77F to 82.4F (World Aquatics). The 75F and 85F tests bracket these comfort ranges.

The index counts days when the typical afternoon high at each metro's main airport reaches 80F.
The index counts days when the typical afternoon high at each metro’s main airport reaches 80F.

Pool season length by city: Swim Season Index ranking of 60 US metros

Seasons range from 365 days in Honolulu to 0 days at four Pacific coast airports. 11 of the 60 metros have at least 180 days at 80F, and 19 have fewer than 90.

Swim Season Index: days with a normal daily high of 80F or more, 60 largest US metros, 1991-2020 normals
SSI rankMetro area (CBSA)Population 2025NOAA station IDStation nameSwim-season days (normal high >= 80F)Swim Season IndexSeason start (80F)Season end (80F)Peak normal high (F)Avg days per year with high >= 80F (1991-2020)Sun Belt (station south of 37N)
1Urban Honolulu, HI988703USW00022521HONOLULU INTL AP, HI US365100.0Year-roundYear-round88.9330.4Yes
2Miami-Fort Lauderdale-West Palm Beach, FL6391072USW00012839MIAMI INTL AP, FL US26572.6Mar 8Nov 2791.0294.2Yes
3Phoenix-Mesa-Chandler, AZ5228938USW00023183PHOENIX SKY HARBOR INTL AP, AZ US23263.6Mar 22Nov 8106.9233.8Yes
4Orlando-Kissimmee-Sanford, FL2957672USW00012815ORLANDO INTL AP, FL US22762.2Mar 25Nov 692.2258.8Yes
5Tampa-St. Petersburg-Clearwater, FL3418895USW00012842TAMPA INTL AP, FL US22361.1Apr 1Nov 991.2247.1Yes
6Tucson, AZ1074685USW00023160TUCSON INTL AP, AZ US21859.7Apr 1Nov 4102.4227.2Yes
7Houston-Pasadena-The Woodlands, TX7904627USW00012960HOUSTON INTERCONT AP, TX US19352.9Apr 15Oct 2495.7209.1Yes
7San Antonio-New Braunfels, TX2813140USW00012921SAN ANTONIO INTL AP, TX US19352.9Apr 14Oct 2396.9212.7Yes
9Austin-Round Rock-San Marcos, TX2620945USW00013904AUSTIN BERGSTROM AP, TX US19252.6Apr 15Oct 2398.1210.8Yes
10Jacksonville, FL1785500USW00013889JACKSONVILLE, FL US18751.2Apr 17Oct 2092.1209.0Yes
11Las Vegas-Henderson-North Las Vegas, NV2407226USW00023169LAS VEGAS MCCARRAN AP, NV US18049.3Apr 22Oct 18104.9187.8Yes
12New Orleans-Metairie, LA970849USW00012916NEW ORLEANS INTL AP, LA US17949.0Apr 23Oct 1891.7198.5Yes
13Riverside-San Bernardino-Ontario, CA4769007USW00003102ONTARIO INTL AP, CA US16444.9May 18Oct 2895.1179.4Yes
14Dallas-Fort Worth-Arlington, TX8477157USW00003927DALLAS FT WORTH AP, TX US16144.1May 5Oct 1297.2181.5Yes
15Fresno, CA1203383USW00093193FRESNO YOSEMITE INTL AP, CA US16043.8May 7Oct 1398.3169.8Yes
16Sacramento-Roseville-Folsom, CA2477274USW00093225SACRAMENTO METRO AP, CA US15542.5May 12Oct 1394.0153.1No
17Birmingham, AL1197766USW00013876BIRMINGHAM AP, AL US15241.6May 7Oct 591.4160.8Yes
18Memphis, TN-MS-AR1341412USW00013893MEMPHIS INTL AP, TN US14740.3May 11Oct 492.2156.4Yes
19Atlanta-Sandy Springs-Roswell, GA6482182USW00013874ATLANTA HARTSFIELD INTL AP, GA US14238.9May 11Sep 2990.4147.2Yes
20Nashville-Davidson-Murfreesboro-Franklin, TN2197416USW00013897NASHVILLE INTL AP, TN US13837.8May 15Sep 2991.1143.1Yes
21Tulsa, OK1069273USW00013968TULSA INTL AP, OK US13537.0May 18Sep 2994.7147.7Yes
22Greenville-Anderson-Greer, SC1014101USW00003870GREER, SC US13436.7May 15Sep 2590.5140.4Yes
23Charlotte-Concord-Gastonia, NC-SC2938830USW00013881CHARLOTTE DOUGLAS AP, NC US13336.4May 16Sep 2590.5143.2Yes
24Raleigh-Cary, NC1595720USW00013722RALEIGH DURHAM INTL AP, NC US13135.9May 17Sep 2491.1140.3Yes
25Oklahoma City, OK1512813USW00013967OKLAHOMA CITY WILL ROGERS AP, OK US13035.6May 20Sep 2694.3147.7Yes
26Knoxville, TN968137USW00013891KNOXVILLE MCGHEE TYSON AP, TN US12634.5May 21Sep 2388.5135.1Yes
27Louisville/Jefferson County, KY-IN1402509USW00093821LOUISVILLE INTL AP, KY US12133.2May 25Sep 2289.1129.4No
28Virginia Beach-Chesapeake-Norfolk, VA-NC1797213USW00013737NORFOLK INTL AP, VA US11732.1May 28Sep 2189.8122.3Yes
28St. Louis, MO-IL2814421USW00013994ST LOUIS LAMBERT INTL AP, MO US11732.1May 26Sep 1989.8126.4No
30Richmond, VA1389338USW00013740RICHMOND INTL AP, VA US11631.8May 27Sep 1989.8131.2No
31Washington-Arlington-Alexandria, DC-VA-MD-WV6465724USW00013743WASHINGTON REAGAN AP, VA US11230.7May 30Sep 1889.9118.2No
32Omaha, NE-IA1009836USW00014942OMAHA EPPLEY AIRFIELD, NE US10729.3May 31Sep 1488.4107.3No
33Baltimore-Columbia-Towson, MD2857781USW00093721BALTIMORE WASH INTL AP, MD US10629.0Jun 2Sep 1589.2111.0No
33Kansas City, MO-KS2270682USW00003947KANSAS CITY INTL AP, MO US10629.0May 31Sep 1388.9112.9No
35Salt Lake City-Murray, UT1308377USW00024127SALT LAKE CITY INTL AP, UT US10528.8Jun 5Sep 1795.5111.0No
36Denver-Aurora-Centennial, CO3092037USW00003017DENVER INTL AP, CO US10227.9Jun 6Sep 1590.5106.7No
37Cincinnati, OH-KY-IN2312858USW00093814CINCINNATI NORTHERN KY AP, KY US10127.7Jun 5Sep 1386.1105.0No
37Philadelphia-Camden-Wilmington, PA-NJ-DE-MD6329118USW00013739PHILADELPHIA INTL AP, PA US10127.7Jun 5Sep 1388.1106.5No
39Indianapolis-Carmel-Greenwood, IN2205695USW00093819INDIANAPOLIS, IN US9726.6Jun 7Sep 1185.4100.6No
40Columbus, OH2242028USW00014821COLUMBUS PORT COLUMBUS INTL AP, OH US9626.3Jun 6Sep 985.699.7No
41San Jose-Sunnyvale-Santa Clara, CA1984473USW00023293SAN JOSE, CA US9425.8Jun 21Sep 2281.980.0No
42New York-Newark-Jersey City, NY-NJ20112448USW00014732NEW YORK LAGUARDIA AP, NY US8824.1Jun 12Sep 786.889.6No
43Chicago-Naperville-Elgin, IL-IN9434123USW00094846CHICAGO OHARE INTL AP, IL US8122.2Jun 14Sep 284.882.2No
44Hartford-West Hartford-East Hartford, CT1171426USW00014740HARTFORD BRADLEY INTL AP, CT US8021.9Jun 16Sep 385.685.8No
45Cleveland, OH2165775USW00014820CLEVELAND, OH US7821.4Jun 16Sep 184.074.2No
46Pittsburgh, PA2421992USW00094823PITTSBURGH INTL AP, PA US7620.8Jun 17Aug 3183.182.2No
47Detroit-Warren-Dearborn, MI4390913USW00094847DETROIT METRO AP, MI US7219.7Jun 16Aug 2684.079.2No
48Grand Rapids-Wyoming-Kentwood, MI1183645USW00094860GRAND RAPIDS, MI US6918.9Jun 17Aug 2483.471.9No
48Bridgeport-Stamford-Danbury, CT978179USW00094702BRIDGEPORT SIKORSKY MEM AP, CT US6918.9Jun 23Aug 3083.867.4No
48Providence-Warwick, RI-MA1708161USW00014765PROVIDENCE T F GREEN AP, RI US6918.9Jun 23Aug 3084.171.9No
51Minneapolis-St. Paul-Bloomington, MN-WI3790295USW00014922MINNEAPOLIS/ST PAUL AP, MN US6417.5Jun 19Aug 2183.870.5No
52Rochester, NY1056149USW00014768ROCHESTER GTR INTL AP, NY US5916.2Jun 24Aug 2182.964.4No
53Portland-Vancouver-Hillsboro, OR-WA2542282USW00024229PORTLAND INTL AP, OR US5815.9Jul 7Sep 283.761.3No
54Milwaukee-Waukesha, WI1575010USW00014839MILWAUKEE MITCHELL AP, WI US5515.1Jun 27Aug 2082.358.5No
55Boston-Cambridge-Newton, MA-NH5034221USW00014739BOSTON LOGAN INTL AP, MA US5414.8Jun 28Aug 2082.562.9No
56Buffalo-Cheektowaga, NY1155653USW00014733BUFFALO, NY US297.9Jul 8Aug 580.654.2No
57San Diego-Chula Vista-Carlsbad, CA3282248USW00023188SAN DIEGO LINDBERGH FLD, CA US00.0NoneNone78.135.3Yes
57Los Angeles-Long Beach-Anaheim, CA12844441USW00023174LOS ANGELES INTL AP, CA US00.0NoneNone77.438.3Yes
57Seattle-Tacoma-Bellevue, WA4161883USW00024233SEATTLE TACOMA INTL AP, WA US00.0NoneNone79.030.6No
57San Francisco-Oakland-Fremont, CA4630041USW00023234SAN FRANCISCO INTL AP, CA US00.0NoneNone75.023.1No

Source: PC&S analysis of NOAA NCEI U.S. Climate Normals 1991-2020 (v1.0.1) and U.S. Census Bureau Vintage 2025. Average-days column is NCEI’s ANN-TMAX-AVGNDS-GRTH080. Download CSV

Longest outdoor swim seasons: 15 large US metros, 1991-2020 normalsDays per year when the normal daily high is 80F or warmer
Longest outdoor swim seasons: 15 large US metros, 1991-2020 normalsHorizontal bar chart. Honolulu has 365 swim-season days at the 80F threshold, followed by Miami (265), Phoenix (232), Orlando (227), Tampa (223) and Tucson (218). Houston and San Antonio have 193 days, Austin 192, Jacksonville 187, Las Vegas 180, New Orleans 179, Riverside (Ontario airport) 164, Dallas-Fort Worth 161 and Fresno 160.Urban Honolulu, HI: 365Urban Honolulu, HI365Miami, FL: 265Miami, FL265Phoenix, AZ: 232Phoenix, AZ232Orlando, FL: 227Orlando, FL227Tampa, FL: 223Tampa, FL223Tucson, AZ: 218Tucson, AZ218Houston, TX: 193Houston, TX193San Antonio, TX: 193San Antonio, TX193Austin, TX: 192Austin, TX192Jacksonville, FL: 187Jacksonville, FL187Las Vegas, NV: 180Las Vegas, NV180New Orleans, LA: 179New Orleans, LA179Riverside, CA: 164Riverside, CA164Dallas, TX: 161Dallas, TX161Fresno, CA: 160Fresno, CA160

Source: PC&S analysis of NOAA NCEI U.S. Climate Normals 1991-2020 (v1.0.1), primary airport stations. Download chart data (CSV)

Shortest outdoor swim seasons: 15 large US metros, 1991-2020 normalsDays per year when the normal daily high is 80F or warmer
Shortest outdoor swim seasons: 15 large US metros, 1991-2020 normalsHorizontal bar chart. Four metros have zero days with a normal high of 80F at their airport station: San Diego, Los Angeles (LAX), Seattle and San Francisco. Buffalo has 29 days, Boston 54, Milwaukee 55, Portland OR 58, Rochester 59 and Minneapolis 64. Pittsburgh has 76 and Detroit 72.San Diego, CA: 0San Diego, CA0Los Angeles, CA: 0Los Angeles, CA0Seattle, WA: 0Seattle, WA0San Francisco, CA: 0San Francisco, CA0Buffalo, NY: 29Buffalo, NY29Boston, MA-NH: 54Boston, MA-NH54Milwaukee, WI: 55Milwaukee, WI55Portland, OR-WA: 58Portland, OR-WA58Rochester, NY: 59Rochester, NY59Minneapolis, MN-WI: 64Minneapolis, MN-WI64Grand Rapids, MI: 69Grand Rapids, MI69Bridgeport, CT: 69Bridgeport, CT69Providence, RI-MA: 69Providence, RI-MA69Detroit, MI: 72Detroit, MI72Pittsburgh, PA: 76Pittsburgh, PA76

Coastal California airport stations sit next to cool ocean water; inland stations in the same metros record longer seasons (see station sensitivity table).

Source: PC&S analysis of NOAA NCEI U.S. Climate Normals 1991-2020 (v1.0.1), primary airport stations. Download chart data (CSV)

Six metros have at least 218 swim-season days at 80F: Honolulu (365), Miami (265), Phoenix (232), Orlando (227), Tampa (223) and Tucson (218), per 1991-2020 normals (NOAA NCEI).

The five most populous metros span 0 to 193 days: New York 88, Los Angeles (LAX) 0, Chicago 81, Dallas-Fort Worth 161 and Houston 193 (1991-2020 normals, NOAA NCEI).

When pool season starts and ends in each US metro

At the 80F threshold, the median season among 55 bounded metros starts on May 27 and ends on Sep 21. Start dates spread from early March in Miami to early July in Buffalo and Portland, Oregon.

Miami’s 80F season starts earliest, on Mar 8, and ends latest, on Nov 27 (1991-2020 normals, NOAA NCEI). Phoenix runs Mar 22 to Nov 8 (NOAA NCEI). Houston runs Apr 15 to Oct 24 (NOAA NCEI).

Northern and Pacific Northwest seasons are short and centred on July: Buffalo runs Jul 8 to Aug 5, Portland, Oregon Jul 7 to Sep 2 and Boston Jun 28 to Aug 20 (1991-2020 normals, NOAA NCEI).

Swim-season days and start and end dates at 75F, 80F and 85F thresholds, 60 largest US metros, 1991-2020 normals
Metro areaNOAA station IDDays >= 75FStart (75F)End (75F)Days >= 80FStart (80F)End (80F)Days >= 85FStart (85F)End (85F)
Urban Honolulu, HIUSW00022521365Year-roundYear-round365Year-roundYear-round171May 20Nov 6
Miami, FLUSW00012839365Year-roundYear-round265Mar 8Nov 27177Apr 29Oct 22
Phoenix, AZUSW00023183258Mar 6Nov 18232Mar 22Nov 8197Apr 14Oct 27
Orlando, FLUSW00012815296Feb 15Dec 7227Mar 25Nov 6176Apr 23Oct 15
Tampa, FLUSW00012842290Feb 22Dec 8223Apr 1Nov 9178Apr 25Oct 19
Tucson, AZUSW00023160248Mar 13Nov 15218Apr 1Nov 4178Apr 26Oct 20
Houston, TXUSW00012960232Mar 21Nov 7193Apr 15Oct 24154May 9Oct 9
San Antonio, TXUSW00012921230Mar 21Nov 5193Apr 14Oct 23151May 10Oct 7
Austin, TXUSW00013904228Mar 23Nov 5192Apr 15Oct 23153May 10Oct 9
Jacksonville, FLUSW00013889234Mar 20Nov 8187Apr 17Oct 20141May 11Sep 28
Las Vegas, NVUSW00023169213Mar 31Oct 29180Apr 22Oct 18153May 8Oct 7
New Orleans, LAUSW00012916218Mar 30Nov 2179Apr 23Oct 18140May 15Oct 1
Riverside, CAUSW00003102219Apr 11Nov 15164May 18Oct 28116Jun 12Oct 5
Dallas, TXUSW00003927198Apr 10Oct 24161May 5Oct 12130May 21Sep 27
Fresno, CAUSW00093193187Apr 21Oct 24160May 7Oct 13131May 24Oct 1
Sacramento, CAUSW00093225183Apr 25Oct 24155May 12Oct 13119Jun 3Sep 29
Birmingham, ALUSW00013876186Apr 16Oct 18152May 7Oct 5114May 30Sep 20
Memphis, TN-MS-ARUSW00013893178Apr 22Oct 16147May 11Oct 4116May 27Sep 19
Atlanta, GAUSW00013874177Apr 21Oct 14142May 11Sep 29102Jun 3Sep 12
Nashville, TNUSW00013897172Apr 24Oct 12138May 15Sep 29103Jun 4Sep 14
Tulsa, OKUSW00013968167Apr 29Oct 12135May 18Sep 29105Jun 3Sep 15
Greenville, SCUSW00003870172Apr 22Oct 10134May 15Sep 2594Jun 6Sep 7
Charlotte, NC-SCUSW00013881173Apr 22Oct 11133May 16Sep 2593Jun 7Sep 7
Raleigh, NCUSW00013722170Apr 24Oct 10131May 17Sep 2493Jun 6Sep 6
Oklahoma City, OKUSW00013967161May 3Oct 10130May 20Sep 2699Jun 6Sep 12
Knoxville, TNUSW00013891162Apr 29Oct 7126May 21Sep 2389Jun 11Sep 7
Louisville/Jefferson County, KY-INUSW00093821154May 5Oct 5121May 25Sep 2288Jun 12Sep 7
Virginia Beach, VA-NCUSW00013737158May 4Oct 8117May 28Sep 2177Jun 15Aug 30
St. Louis, MO-ILUSW00013994147May 9Oct 2117May 26Sep 1985Jun 11Sep 3
Richmond, VAUSW00013740156May 2Oct 4116May 27Sep 1982Jun 13Sep 2
Washington, DC-VA-MD-WVUSW00013743145May 10Oct 1112May 30Sep 1880Jun 15Sep 2
Omaha, NE-IAUSW00014942134May 17Sep 27107May 31Sep 1467Jun 17Aug 22
Baltimore, MDUSW00093721137May 15Sep 28106Jun 2Sep 1573Jun 17Aug 28
Kansas City, MO-KSUSW00003947135May 16Sep 27106May 31Sep 1372Jun 18Aug 28
Salt Lake City, UTUSW00024127129May 22Sep 27105Jun 5Sep 1781Jun 18Sep 6
Denver, COUSW00003017125May 25Sep 26102Jun 6Sep 1572Jun 20Aug 30
Cincinnati, OH-KY-INUSW00093814132May 18Sep 26101Jun 5Sep 1357Jun 27Aug 22
Philadelphia, PA-NJ-DE-MDUSW00013739131May 19Sep 26101Jun 5Sep 1365Jun 21Aug 24
Indianapolis, INUSW00093819126May 22Sep 2497Jun 7Sep 1132Jul 2Aug 2
Columbus, OHUSW00014821127May 20Sep 2396Jun 6Sep 935Jul 1Aug 4
San Jose, CAUSW00023293150May 24Oct 2094Jun 21Sep 220NoneNone
New York, NY-NJUSW00014732119May 27Sep 2288Jun 12Sep 746Jun 30Aug 14
Chicago, IL-INUSW00094846112May 29Sep 1781Jun 14Sep 20NoneNone
Hartford, CTUSW00014740113May 29Sep 1880Jun 16Sep 325Jul 8Aug 1
Cleveland, OHUSW00014820112May 30Sep 1878Jun 16Sep 10NoneNone
Pittsburgh, PAUSW00094823111May 29Sep 1676Jun 17Aug 310NoneNone
Detroit, MIUSW00094847108May 30Sep 1472Jun 16Aug 260NoneNone
Grand Rapids, MIUSW00094860105Jun 1Sep 1369Jun 17Aug 240NoneNone
Bridgeport, CTUSW00094702103Jun 7Sep 1769Jun 23Aug 300NoneNone
Providence, RI-MAUSW00014765101Jun 7Sep 1569Jun 23Aug 300NoneNone
Minneapolis, MN-WIUSW00014922101Jun 2Sep 1064Jun 19Aug 210NoneNone
Rochester, NYUSW00014768100Jun 5Sep 1259Jun 24Aug 210NoneNone
Portland, OR-WAUSW0002422995Jun 20Sep 2258Jul 7Sep 20NoneNone
Milwaukee, WIUSW0001483995Jun 10Sep 1255Jun 27Aug 200NoneNone
Boston, MA-NHUSW0001473991Jun 12Sep 1054Jun 28Aug 200NoneNone
Buffalo, NYUSW0001473388Jun 13Sep 829Jul 8Aug 50NoneNone
San Diego, CAUSW0002318892Jul 11Oct 100NoneNone0NoneNone
Los Angeles, CAUSW0002317484Jul 12Oct 30NoneNone0NoneNone
Seattle, WAUSW0002423362Jul 4Sep 30NoneNone0NoneNone
San Francisco, CAUSW000232345Sep 15Sep 190NoneNone0NoneNone

Source: PC&S analysis of NOAA NCEI U.S. Climate Normals 1991-2020 daily files. Download CSV

Season start dates at the 80F threshold range from March in South Florida to July in the Great Lakes and Pacific Northwest.
Season start dates at the 80F threshold range from March in South Florida to July in the Great Lakes and Pacific Northwest.

Regional patterns in swim-season length: Sun Belt, Florida, desert Southwest and Pacific coast

Latitude explains most of the ranking (Spearman rho -0.82), with the cool Pacific coast as the main exception. The 28 Sun Belt metros average 151.2 population-weighted days at 80F, 1.86 times the 81.4 days in the 32 other metros.

Swim-season days by group at 75F, 80F and 85F: mean, population-weighted and median, 60 largest US metros, 1991-2020 normals and 2025 populations
GroupMetrosPopulation 2025Mean days 75FPop-weighted days 75FMedian days 75FMean days 80FPop-weighted days 80FMedian days 80FMean days 85FPop-weighted days 85FMedian days 85F
All 60 metros60198927698159.4155.0148.5121.0113.5114.075.271.180.5
Sun Belt metros (south of 37N)2891253351208.3203.1192.5165.1151.2160.5122.5114.5123.0
Other metros (37N and north)32107674347116.6114.3116.082.481.484.533.734.412.5

Source: PC&S analysis of NOAA NCEI normals and U.S. Census Bureau Vintage 2025. Download CSV

Population-weighted swim-season days: Sun Belt vs other large US metros, 1991-2020 normalsSun Belt = primary station south of 37 degrees N; weights = July 1, 2025 Census population
Population-weighted swim-season days: Sun Belt vs other large US metros, 1991-2020 normalsGrouped bar chart. At 80F the 28 Sun Belt metros average 151.2 population-weighted days against 81.4 days for the 32 other metros; all 60 metros average 113.5. At 75F the figures are 203.1, 114.3 and 155.0. At 85F they are 114.5, 34.4 and 71.1.062.5125188250All 60 metros: 155All 60 metrosSun Belt metros (south of 37N): 203Sun Belt metros (south of 37N)Other metros (37N and north): 114Other metros (37N and north)

Source: PC&S analysis of NOAA NCEI U.S. Climate Normals 1991-2020 (v1.0.1), primary airport stations; U.S. Census Bureau Vintage 2025. Download chart data (CSV)

Population is moving toward longer seasons. The 28 Sun Belt metros grew by 4,639,666 residents (+5.4%) between July 1, 2020 and July 1, 2025, against 1,470,350 (+1.4%) in the 32 other metros (U.S. Census Bureau). Reweighting the same 1991-2020 normals from 2020 to 2025 populations raises the 60-metro average from 111.64 to 113.46 days.

Florida: Miami’s normal monthly high is at or above 80F in 9 months and at or above 75F in all 12 months; its coolest month, January, has a normal high of 76.2F (NOAA NCEI). Orlando and Tampa reach 80F in 7 months, and Jacksonville in 6 months (1991-2020 monthly normals).

Desert Southwest: Phoenix (232 days), Tucson (218) and Las Vegas (180) have long 80F seasons, and Phoenix’s peak normal high is 106.9F on Jul 4 (1991-2020 normals, NOAA NCEI).

Pacific coast: the four zero-day airports (LAX, San Diego, SFO and Seattle-Tacoma) have peak normal highs between 75.0F and 79.0F (1991-2020 normals, NOAA NCEI). Inland California stations are much warmer: Riverside-San Bernardino (Ontario airport) has 164 days and Fresno 160.

Normal monthly high temperature in six US cities, 1991-2020Degrees F, primary airport station
Normal monthly high temperature in six US cities, 1991-2020Line chart of normal monthly highs. Miami stays between 76.2F in January and 90.7F in August. Phoenix rises from 67.6F in January to a July peak above 106F. Houston and Atlanta follow a similar arc at lower levels. New York runs from 40.2F in January into the mid 80s in July, and Seattle peaks in the high 70s, never reaching an 80F monthly normal.0306090120JanFebMarAprMayJunJulAugSepOctNovDecPhoenix, AZ, Jan: 67.6Phoenix, AZ, Feb: 70.8Phoenix, AZ, Mar: 78.1Phoenix, AZ, Apr: 85.5Phoenix, AZ, May: 94.5Phoenix, AZ, Jun: 104Phoenix, AZ, Jul: 106Phoenix, AZ, Aug: 105Phoenix, AZ, Sep: 100Phoenix, AZ, Oct: 89.2Phoenix, AZ, Nov: 76.5Phoenix, AZ, Dec: 66.2Phoenix, AZMiami, FL, Jan: 76.2Miami, FL, Feb: 78.2Miami, FL, Mar: 80.6Miami, FL, Apr: 83.6Miami, FL, May: 86.7Miami, FL, Jun: 89.3Miami, FL, Jul: 90.6Miami, FL, Aug: 90.7Miami, FL, Sep: 89Miami, FL, Oct: 85.9Miami, FL, Nov: 81.3Miami, FL, Dec: 78.2Miami, FLHouston, TX, Jan: 63.8Houston, TX, Feb: 67.8Houston, TX, Mar: 74Houston, TX, Apr: 80.1Houston, TX, May: 86.9Houston, TX, Jun: 92.3Houston, TX, Jul: 94.5Houston, TX, Aug: 94.9Houston, TX, Sep: 90.4Houston, TX, Oct: 82.8Houston, TX, Nov: 72.6Houston, TX, Dec: 65.3Houston, TXAtlanta, GA, Jan: 54Atlanta, GA, Feb: 58.2Atlanta, GA, Mar: 65.9Atlanta, GA, Apr: 73.8Atlanta, GA, May: 81.1Atlanta, GA, Jun: 87.1Atlanta, GA, Jul: 90.1Atlanta, GA, Aug: 89Atlanta, GA, Sep: 83.9Atlanta, GA, Oct: 74.4Atlanta, GA, Nov: 64.1Atlanta, GA, Dec: 56.2Atlanta, GANew York, NY-NJ, Jan: 40.2New York, NY-NJ, Feb: 42.7New York, NY-NJ, Mar: 49.9New York, NY-NJ, Apr: 61.3New York, NY-NJ, May: 71.8New York, NY-NJ, Jun: 81.1New York, NY-NJ, Jul: 86.4New York, NY-NJ, Aug: 84.5New York, NY-NJ, Sep: 77.2New York, NY-NJ, Oct: 66New York, NY-NJ, Nov: 55New York, NY-NJ, Dec: 45.4New York, NY-NJSeattle, WA, Jan: 48Seattle, WA, Feb: 50.3Seattle, WA, Mar: 54.2Seattle, WA, Apr: 59.3Seattle, WA, May: 66.3Seattle, WA, Jun: 71.1Seattle, WA, Jul: 77.4Seattle, WA, Aug: 77.6Seattle, WA, Sep: 71.6Seattle, WA, Oct: 60.5Seattle, WA, Nov: 52.1Seattle, WA, Dec: 47Seattle, WA

Source: NOAA NCEI U.S. Climate Normals 1991-2020, monthly MLY-TMAX-NORMAL. Download chart data (CSV)

Sensitivity of the swim-season index to threshold, station and method

Moving the threshold from 80F to 75F adds about 41.5 population-weighted days, and moving it to 85F removes about 42.4. Station choice can move a coastal metro from 0 to more than 100 days, while inland metros barely change.

Swim-season days at 85F, 80F and 75F thresholds, 60 largest US metros, 1991-2020 normalsBar runs from the 85F count (low) to the 75F count (high); dot = 80F primary threshold
Swim-season days at 85F, 80F and 75F thresholds, 60 largest US metros, 1991-2020 normalsRange chart for 60 metros. Each range spans the count of days at the 85F threshold to the count at 75F, with a dot at 80F. Honolulu runs from 171 to 365 days, Miami from 177 to 365, Phoenix from 197 to 258. Mid-Atlantic and Midwest metros span roughly 30 to 150 days. Coastal California and Seattle stations show 0 days at 85F and 80F and between 5 and 92 days at 75F.0100200300400Urban Honolulu, HI: 171 to 365, point 365Urban Honolulu, HIMiami, FL: 177 to 365, point 265Miami, FLPhoenix, AZ: 197 to 258, point 232Phoenix, AZOrlando, FL: 176 to 296, point 227Orlando, FLTampa, FL: 178 to 290, point 223Tampa, FLTucson, AZ: 178 to 248, point 218Tucson, AZHouston, TX: 154 to 232, point 193Houston, TXSan Antonio, TX: 151 to 230, point 193San Antonio, TXAustin, TX: 153 to 228, point 192Austin, TXJacksonville, FL: 141 to 234, point 187Jacksonville, FLLas Vegas, NV: 153 to 213, point 180Las Vegas, NVNew Orleans, LA: 140 to 218, point 179New Orleans, LARiverside, CA: 116 to 219, point 164Riverside, CADallas, TX: 130 to 198, point 161Dallas, TXFresno, CA: 131 to 187, point 160Fresno, CASacramento, CA: 119 to 183, point 155Sacramento, CABirmingham, AL: 114 to 186, point 152Birmingham, ALMemphis, TN-MS-AR: 116 to 178, point 147Memphis, TN-MS-ARAtlanta, GA: 102 to 177, point 142Atlanta, GANashville, TN: 103 to 172, point 138Nashville, TNTulsa, OK: 105 to 167, point 135Tulsa, OKGreenville, SC: 94 to 172, point 134Greenville, SCCharlotte, NC-SC: 93 to 173, point 133Charlotte, NC-SCRaleigh, NC: 93 to 170, point 131Raleigh, NCOklahoma City, OK: 99 to 161, point 130Oklahoma City, OKKnoxville, TN: 89 to 162, point 126Knoxville, TNLouisville/Jefferson County, KY-IN: 88 to 154, point 121Louisville/Jefferson County, KY-INVirginia Beach, VA-NC: 77 to 158, point 117Virginia Beach, VA-NCSt. Louis, MO-IL: 85 to 147, point 117St. Louis, MO-ILRichmond, VA: 82 to 156, point 116Richmond, VAWashington, DC-VA-MD-WV: 80 to 145, point 112Washington, DC-VA-MD-WVOmaha, NE-IA: 67 to 134, point 107Omaha, NE-IABaltimore, MD: 73 to 137, point 106Baltimore, MDKansas City, MO-KS: 72 to 135, point 106Kansas City, MO-KSSalt Lake City, UT: 81 to 129, point 105Salt Lake City, UTDenver, CO: 72 to 125, point 102Denver, COCincinnati, OH-KY-IN: 57 to 132, point 101Cincinnati, OH-KY-INPhiladelphia, PA-NJ-DE-MD: 65 to 131, point 101Philadelphia, PA-NJ-DE-MDIndianapolis, IN: 32 to 126, point 97Indianapolis, INColumbus, OH: 35 to 127, point 96Columbus, OHSan Jose, CA: 0 to 150, point 94San Jose, CANew York, NY-NJ: 46 to 119, point 88New York, NY-NJChicago, IL-IN: 0 to 112, point 81Chicago, IL-INHartford, CT: 25 to 113, point 80Hartford, CTCleveland, OH: 0 to 112, point 78Cleveland, OHPittsburgh, PA: 0 to 111, point 76Pittsburgh, PADetroit, MI: 0 to 108, point 72Detroit, MIGrand Rapids, MI: 0 to 105, point 69Grand Rapids, MIBridgeport, CT: 0 to 103, point 69Bridgeport, CTProvidence, RI-MA: 0 to 101, point 69Providence, RI-MAMinneapolis, MN-WI: 0 to 101, point 64Minneapolis, MN-WIRochester, NY: 0 to 100, point 59Rochester, NYPortland, OR-WA: 0 to 95, point 58Portland, OR-WAMilwaukee, WI: 0 to 95, point 55Milwaukee, WIBoston, MA-NH: 0 to 91, point 54Boston, MA-NHBuffalo, NY: 0 to 88, point 29Buffalo, NYSan Diego, CA: 0 to 92, point 0San Diego, CALos Angeles, CA: 0 to 84, point 0Los Angeles, CASeattle, WA: 0 to 62, point 0Seattle, WASan Francisco, CA: 0 to 5, point 0San Francisco, CA

Source: PC&S analysis of NOAA NCEI U.S. Climate Normals 1991-2020 (v1.0.1), primary airport stations. Download chart data (CSV)

Population-weighted swim-season days across the 60 metros are 155.0 at 75F, 113.5 at 80F and 71.1 at 85F (1991-2020 normals, 2025 populations). At 85F, 18 metros have no swim-season days; at 75F, Honolulu and Miami are year-round.

Swim-season days at alternate NOAA stations in seven metros, 1991-2020 normals
Metro areaNOAA station IDStation nameRoleDays >= 75FDays >= 80FDays >= 85F
New York, NY-NJUSW00014732NEW YORK LAGUARDIA AP, NY USPrimary1198846
New York, NY-NJUSW00094728NEW YORK CNTRL PK TWR, NY USAlternate1128119
New York, NY-NJUSW00094789NEW YORK JFK INTL AP, NY USAlternate104720
Los Angeles, CAUSW00023174LOS ANGELES INTL AP, CA USPrimary8400
Los Angeles, CAUSW00093134LOS ANGELES DWTN USC CAMPUS, CA USAlternate157980
Los Angeles, CAUSW00023152BURBANK GLENDALE PASADENA AP, CA USAlternate18412081
Riverside, CAUSW00003102ONTARIO INTL AP, CA USPrimary219164116
Riverside, CAUSW00003171RIVERSIDE MUNI AP, CA USAlternate222164119
San Francisco, CAUSW00023234SAN FRANCISCO INTL AP, CA USPrimary500
San Francisco, CAUSW00023230OAKLAND METRO INTL AP, CA USAlternate000
Austin, TXUSW00013904AUSTIN BERGSTROM AP, TX USPrimary228192153
Austin, TXUSW00013958AUSTIN-CAMP MABRY, TX USAlternate229193154
Sacramento, CAUSW00093225SACRAMENTO METRO AP, CA USPrimary183155119
Sacramento, CAUSW00023232SACRAMENTO EXECUTIVE AP, CA USAlternate183152119
Sacramento, CAUSW00023271SACRAMENTO 5 ESE, CA USAlternate187156123
San Diego, CAUSW00023188SAN DIEGO LINDBERGH FLD, CA USPrimary9200
San Diego, CAUSW00003131SAN DIEGO MONTGOMERY FLD, CA USAlternate142730

Source: PC&S analysis of NOAA NCEI U.S. Climate Normals 1991-2020 daily files; station inventory from NCEI. Download CSV

New York: LaGuardia records 88 days at 80F, Central Park 81 and JFK 72 (1991-2020 normals, NOAA NCEI). San Diego: Lindbergh Field records 0 days at 80F and Montgomery Field 73. Austin, Sacramento and Riverside stations differ by 4 days or fewer.

Normal curve vs observed days: NCEI also publishes the average number of observed days per year with a high at or above 80F (NCEI variable definitions). That count exceeds the normal-curve count by a median of 7.1 days across the 60 metros, with the largest gap at LAX (+38.3 days). Honolulu is the reverse case: the normal curve never drops below 80F, but observed highs reached 80F on an average of 330.4 days a year.

Climate-based pool season vs DOE pool pump season assumptions by state

DOE’s pool pump rulemaking assigns each state an operating season of 3 to 12 months. Those windows describe when pumps run, not when the air is warm enough to swim, and they exceed the NOAA 80F season in 59 of the 60 metros.

DOE pool pump operating window vs NOAA swim-season days, 60 largest US metros (DOE 2016 analysis; NOAA 1991-2020 normals)
Metro areaState usedDOE pool-use windowDOE season daysNOAA days >= 75FNOAA days >= 80FDifference: DOE minus NOAA 80F days
Urban Honolulu, HIHI1/1-12/313653653650
Miami, FLFL1/1-12/31365365265100
Phoenix, AZAZ1/1-12/31365258232133
Orlando, FLFL1/1-12/31365296227138
Tampa, FLFL1/1-12/31365290223142
Tucson, AZAZ1/1-12/31365248218147
Houston, TXTX1/1-12/31365232193172
San Antonio, TXTX1/1-12/31365230193172
Austin, TXTX1/1-12/31365228192173
Jacksonville, FLFL1/1-12/31365234187178
Las Vegas, NVNV1/1-12/31365213180185
New Orleans, LALA1/1-12/31365218179186
Riverside, CACA1/1-12/31365219164201
Dallas, TXTX1/1-12/31365198161204
Fresno, CACA1/1-12/31365187160205
Sacramento, CACA1/1-12/31365183155210
Birmingham, ALAL1/1-12/31365186152213
Memphis, TN-MS-ARTN1/1-12/31365178147218
Atlanta, GAGA4/1-10/3121417714272
Nashville, TNTN1/1-12/31365172138227
Tulsa, OKOK1/1-12/31365167135230
Greenville, SCSC4/1-10/3121417213480
Charlotte, NC-SCNC4/1-10/3121417313381
Raleigh, NCNC4/1-10/3121417013183
Oklahoma City, OKOK1/1-12/31365161130235
Knoxville, TNTN1/1-12/31365162126239
Louisville/Jefferson County, KY-INKY1/1-12/31365154121244
Virginia Beach, VA-NCVA4/1-10/3121415811797
St. Louis, MO-ILMO6/1-9/301221471175
Richmond, VAVA4/1-10/3121415611698
Washington, DC-VA-MD-WVDC5/1-9/3015314511241
Omaha, NE-IANE6/1-9/3012213410715
Baltimore, MDMD5/1-9/3015313710647
Kansas City, MO-KSMO6/1-9/3012213510616
Salt Lake City, UTUT5/1-8/3112312910518
Denver, COCO5/1-8/3112312510221
Cincinnati, OH-KY-INOH5/1-8/3112313210122
Philadelphia, PA-NJ-DE-MDPA5/1-8/3112313110122
Indianapolis, ININ5/1-8/311231269726
Columbus, OHOH5/1-8/311231279627
San Jose, CACA1/1-12/3136515094271
New York, NY-NJNY5/1-8/311231198835
Chicago, IL-INIL5/1-8/311231128142
Hartford, CTCT5/1-8/311231138043
Cleveland, OHOH5/1-8/311231127845
Pittsburgh, PAPA5/1-8/311231117647
Detroit, MIMI5/1-8/311231087251
Grand Rapids, MIMI5/1-8/311231056954
Bridgeport, CTCT5/1-8/311231036954
Providence, RI-MARI5/1-8/311231016954
Minneapolis, MN-WIMN6/1-9/301221016458
Rochester, NYNY5/1-8/311231005964
Portland, OR-WAOR6/1-8/3192955834
Milwaukee, WIWI6/1-9/30122955567
Boston, MA-NHMA5/1-8/31123915469
Buffalo, NYNY5/1-8/31123882994
San Diego, CACA1/1-12/31365920365
Los Angeles, CACA1/1-12/31365840365
Seattle, WAWA6/1-8/319262092
San Francisco, CACA1/1-12/3136550365

Source: DOE DPPP Technical Support Document (2016), Table 7.3.11, as used in PC&S cost to run a pool pump; NOAA NCEI normals. Download CSV

DOE assumes year-round pool pump operation in 27 of the 60 metros, including all of Florida, Texas, Arizona and California (DOE); 21 of those 27 metros have fewer than 200 days at 80F in the 1991-2020 normals. DOE states that its assumptions draw on its Energy Saver website and PK Data rather than on station temperatures.

In the 23 metros in DOE’s 4-month cold-state group, the median NOAA 80F season is 80 days, against DOE windows of 122 or 123 days. At the 75F threshold, the NOAA season is longer than DOE’s window in 10 metros, including St. Louis, Denver and Philadelphia.

The PC&S pool pump cost report uses DOE’s state windows for its season-based estimates; the climate counts in this report are a cross-check on those windows, not a replacement.

2025 swim-season days compared with the 1991-2020 normals

NOAA ranked 2025 as the fourth-warmest year on record for the contiguous US. Six of seven checked airport stations logged more 80F days in 2025 than their 1991-2020 average, led by Houston at +49.9 days.

Observed days with a high of 80F or more in 2025 vs the 1991-2020 average, 7 US airport stations
Metro areaNOAA station IDDays with 2025 dataActual days with high >= 80F in 20251991-2020 average days with high >= 80F2025 minus 1991-2020 averageNormal-curve swim-season days (80F)
Miami, FLUSW00012839365310294.215.8265
Houston, TXUSW00012960365259209.149.9193
Atlanta, GAUSW00013874365170147.222.8142
New York, NY-NJUSW000147323658689.6-3.688
Phoenix, AZUSW00023183365254233.820.2232
Seattle, WAUSW000242333653430.63.40
Chicago, IL-INUSW000948463659182.28.881

Source: NOAA NCEI GHCN-Daily via Access Data Service (2025); NOAA NCEI normals ANN-TMAX-AVGNDS-GRTH080. Download CSV

Days with a high of 80F or more in 2025 vs the 1991-2020 average, 7 US airport stations2025 = observed GHCN-Daily count; average = NCEI normals ANN-TMAX-AVGNDS-GRTH080
Days with a high of 80F or more in 2025 vs the 1991-2020 average, 7 US airport stationsPaired bar chart for 7 stations. Houston recorded 259 days at 80F or warmer in 2025 against a 1991-2020 average of 209.1. Miami recorded 310 vs 294.2, Phoenix 254 vs 233.8, Atlanta 170 vs 147.2, Chicago O'Hare 91 vs 82.2, Seattle 34 vs 30.6, and New York LaGuardia 86 vs 89.6, the only station below its average.0100200300400Miami, FL: 310Miami, FLHouston, TX: 259Houston, TXAtlanta, GA: 170Atlanta, GANew York, NY-NJ: 86New York, NY-NJPhoenix, AZ: 254Phoenix, AZSeattle, WA: 34Seattle, WAChicago, IL-IN: 91Chicago, IL-IN

Single-year comparison only; one warm year is not a trend.

Source: NOAA NCEI GHCN-Daily (2025) and U.S. Climate Normals 1991-2020. Download chart data (CSV)

The contiguous US averaged 54.6F in 2025, 2.6F above the 20th-century average and the fourth-warmest year in NOAA’s 131-year record (NOAA NCEI). Miami’s airport logged 310 days at or above 80F in 2025, Phoenix 254 and Atlanta 170 (NOAA NCEI GHCN-Daily).

Next normals: NCEI produces official normals every 10 years (NOAA NCEI), and NOAA’s 2021 release noted that 1991-2020 normals were warmer than 1981-2010 across the South and Southwest (NOAA NCEI). The next set, covering 2001 to 2030, cannot be computed until the 2030 data year is complete.

What the climate data says about opening and closing a pool

Pool opening dates in practice depend on equipment, water chemistry, heating and local schedules, not only on air temperature. The climate season gives a neutral benchmark for each metro.

Municipal schedules can be far shorter than the climate season. San Antonio opened 23 outdoor city pools on June 20, 2026, after 7 pre-season pools opened on May 23, 2026 (City of San Antonio); the San Antonio airport’s 80F season runs Apr 14 to Oct 23 in the 1991-2020 normals (NOAA NCEI).

A pool-owner survey by Swim University reports that most of 1,900 respondents open between May 1 and May 15 (Swim University); the survey’s sample, dates and method are not published, so the figure is context only.

Season length also drives running and heating costs; see the PC&S reports on the cost to run a pool pump and the cost to heat a pool. Installed-pool counts are in number of swimming pools in the US.

At the 80F threshold, the median season among bounded metros ends on September 21.
At the 80F threshold, the median season among bounded metros ends on September 21.

Index results

  1. Honolulu: 365 swim-season days at 80F (Swim Season Index 100), Honolulu International Airport (USW00022521), 1991-2020 normals (NOAA NCEI).
  2. Miami-Fort Lauderdale-West Palm Beach: 265 days at 80F, Mar 8 to Nov 27, and 365 days at 75F, Miami International Airport (USW00012839), 1991-2020 normals (NOAA NCEI).
  3. Phoenix-Mesa-Chandler: 232 days at 80F, Mar 22 to Nov 8, Sky Harbor (USW00023183), 1991-2020 normals (NOAA NCEI).
  4. Orlando (227 days) and Tampa (223 days) have the next-longest 80F seasons in Florida after Miami, while Jacksonville has 187 days, 1991-2020 normals (NOAA NCEI).
  5. Houston (193 days), San Antonio (193 days) and Austin (192 days) lead Texas at 80F; Dallas-Fort Worth has 161 days, 1991-2020 normals (NOAA NCEI).
  6. New York-Newark-Jersey City: 88 days at 80F (Jun 12 to Sep 7) at LaGuardia (USW00014732), 1991-2020 normals (NOAA NCEI).
  7. Chicago-Naperville-Elgin: 81 days at 80F (Jun 14 to Sep 2) at O’Hare (USW00094846), 1991-2020 normals (NOAA NCEI).
  8. Boston-Cambridge-Newton: 54 days at 80F (Jun 28 to Aug 20) at Logan (USW00014739), 1991-2020 normals (NOAA NCEI).
  9. Buffalo-Cheektowaga: 29 days at 80F (Jul 8 to Aug 5), the shortest bounded season of the 60 metros, 1991-2020 normals (NOAA NCEI).
  10. Los Angeles (LAX), San Diego (Lindbergh Field), San Francisco (SFO) and Seattle-Tacoma record 0 days with a normal high of 80F in 1991-2020; at 75F the counts are 84, 92, 5 and 62 days (NOAA NCEI).
  11. Station choice matters on the California coast: Burbank airport records 120 days at 80F and downtown Los Angeles (USC campus) 98 days, against 0 at LAX, 1991-2020 normals (NOAA NCEI).
  12. Station latitude and 80F season length have a Spearman rank correlation of -0.82 across the 60 metros (1991-2020 normals, NOAA NCEI).
  13. DOE’s pool pump operating-season assumptions are longer than the NOAA 80F season in 59 of the 60 metros and equal in Honolulu; DOE assumes year-round operation in 27 of the 60 metros (DOE, 2016).
  14. At the 85F threshold, 18 of the 60 metros have no swim-season days, and at 75F every metro has at least 5 days (1991-2020 normals, NOAA NCEI).
  15. In 2025, 6 of 7 checked airport stations recorded more days at or above 80F than their 1991-2020 average; New York LaGuardia was the exception at 86 days vs 89.6 (NOAA NCEI GHCN-Daily).

Scores, ranks and sensitivity

Swim Season Index ranking

Which large US metros have the longest and shortest outdoor swim seasons?

FormulaSSI = days with DLY-TMAX-NORMAL >= 80F / 365 x 100, per primary airport station

Inputs: fact rows #82 to #141 (station normals), derived rows #162 to #221

Honolulu scores 100, Miami 72.6, Phoenix 63.6 and Orlando 62.2; Buffalo scores 7.9 and four Pacific coast airports score 0 (1991-2020 normals).

Limitations: One airport station per metro; air temperature, not water; normals are smoothed 30-year curves.

Threshold sensitivity at 75F, 80F and 85F

How much does the definition of a swim day change the answer?

FormulaRepeat the day count at 75F and 85F; population-weight each

Inputs: derived rows #162 to #221, #222, #225

Population-weighted days: 155.0 at 75F, 113.5 at 80F and 71.1 at 85F. At 85F, 18 of 60 metros have no days.

Limitations: Thresholds are proxies for comfort; no single air temperature defines swimmable weather.

Season start and end dates

When does the typical outdoor swim season begin and end?

FormulaFirst and last day of the longest unbroken run of qualifying days; median day-of-year across metros

Inputs: derived rows #162 to #221, #226

Median 80F season among 55 bounded metros: May 27 to Sep 21. Earliest start Miami (Mar 8); latest start Buffalo (Jul 8).

Limitations: Excludes year-round Honolulu and the four zero-day metros.

Population-weighted average season

How long is the swim season where large-metro Americans live?

Formulasum(population 2025 x days) / sum(population 2025)

Inputs: fact rows #22 to #81 (Census), derived rows #162 to #221, #222, #229

113.5 days at 80F for 198,927,698 residents of the 60 metros; using 2020 populations gives 111.64 days, so population shifts alone added 1.8 days.

Limitations: Whole-metro population is weighted by a single airport’s climate.

Sun Belt vs rest

How much longer is the season in Sun Belt metros?

FormulaPopulation-weighted days80 for stations south of 37.0N vs the rest; difference and ratio

Inputs: fact rows #82 to #141, #22 to #81, derived rows #227, #228

151.2 days in 28 Sun Belt metros vs 81.4 in 32 other metros: 69.8 days longer, a ratio of 1.86. The Sun Belt group took 75.9% of 2020 to 2025 population growth across the 60 metros.

Limitations: Latitude cut-off is a proxy; coastal California sits inside the Sun Belt group but has short airport seasons.

DOE operating season cross-check

Do DOE pool pump season assumptions match the climate?

FormulaDOE window days minus NOAA days80 per metro

Inputs: fact row #17, derived rows #231, #232

DOE’s window is longer than the 80F season in 59 of 60 metros, by a mean of 119.9 days.

Limitations: DOE windows describe pump operation and come from 2016 modelling assumptions.

Download the calculation sheet (CSV)

Takeaways

  • Across the 60 largest US metros, the population-weighted swim season is 113.5 days a year at an 80F normal daily high, based on NOAA’s 1991-2020 normals (NOAA NCEI) and July 1, 2025 populations (U.S. Census Bureau).
  • Honolulu is the only one of the 60 metros where the 1991-2020 normal daily high stays at or above 80F all year; its lowest normal daily high is 80.4F (NOAA NCEI).
  • In the contiguous US, Miami has the longest 80F season at 265 days (Mar 8 to Nov 27), followed by Phoenix at 232 days and Orlando at 227 days, per 1991-2020 normals (NOAA NCEI).
  • Buffalo has the shortest bounded season among the 60 metros at 29 days (Jul 8 to Aug 5), and four airport stations (Los Angeles LAX, San Diego, San Francisco SFO and Seattle-Tacoma) never reach an 80F normal high in 1991-2020 normals (NOAA NCEI).
  • The median 80F season among the 55 metros with a start and end date runs from May 27 to Sep 21 (1991-2020 normals, NOAA NCEI).
  • The 28 Sun Belt metros average 151.2 population-weighted swim-season days against 81.4 days for the 32 other metros, a gap of 69.8 days (1991-2020 normals, 2025 populations).
  • The 28 Sun Belt metros absorbed 75.9% of the 60 metros’ population growth between July 1, 2020 and July 1, 2025 (U.S. Census Bureau), which lifted the population-weighted season by 1.8 days with climate held constant.
  • In 2025, Houston’s airport recorded 259 days with a high of 80F or more against a 1991-2020 average of 209.1 days (NOAA NCEI GHCN-Daily).

Questions this index answers

When is pool season?

For the 60 largest US metros, the median outdoor swim season at an 80F normal daily high runs from May 27 to Sep 21, based on NOAA’s 1991-2020 normals (NOAA NCEI). Miami’s season runs Mar 8 to Nov 27, New York’s Jun 12 to Sep 7.

Which US city has the longest swimming season?

Honolulu: its 1991-2020 normal daily high stays at or above 80F all 365 days (NOAA NCEI). In the contiguous US, Miami leads with 265 days, followed by Phoenix with 232.

How warm does it need to be to swim outside?

No single standard exists. The NWS Baltimore/Washington office says most people are comfortable in 70F to 78F water (NWS), and World Aquatics sets competition pools at 25C to 28C, or 77F to 82.4F (World Aquatics). This index uses an 80F air high as its primary threshold, with 75F and 85F tests.

How many months can you swim in Florida?

Miami’s normal monthly high is 80F or more in 9 months and 75F or more in all 12; Orlando and Tampa reach 80F in 7 months and Jacksonville in 6 (1991-2020 monthly normals, NOAA NCEI).

When should I open my pool?

The climate data gives a benchmark: the median 80F season among large US metros starts on May 27, ranging from Mar 8 in Miami to Jul 8 in Buffalo (1991-2020 normals, NOAA NCEI). Opening for maintenance usually comes before swimming weather; check your own equipment and local conditions.

Data vintage

  • First edition of the Swim Season Index, built on NOAA NCEI’s 1991-2020 U.S. Climate Normals (v1.0.1) and Census Vintage 2025 metro populations.
  • U.S. Census Bureau released Vintage 2025 metro population estimates on March 26, 2026; Houston (+126,720) and Dallas-Fort Worth (+123,557) led numeric growth from July 1, 2024 to July 1, 2025 (U.S. Census Bureau).
  • NOAA NCEI ranked 2025 as the fourth-warmest year in the 131-year record for the contiguous US, at 54.6F, 2.6F above the 20th-century average (NOAA NCEI, published January 13, 2026).
  • NCEI reissued the 1991-2020 normals statistics for 23 sites as version 1.0.1; the normals were first released in May 2021 as version 1.0.0 (NOAA NCEI).

FAQ

What is the Swim Season Index?

The Swim Season Index is the number of days per year with a 1991-2020 normal daily high of 80F or more at a metro’s main airport, divided by 365 and multiplied by 100. Miami scores 72.6 (NOAA NCEI).

How long is pool season in Phoenix?

Phoenix Sky Harbor (USW00023183) has 232 days at an 80F normal high, from Mar 22 to Nov 8, and 258 days at 75F (1991-2020 normals, NOAA NCEI).

How long is pool season in Texas cities?

At 80F, Houston has 193 days, San Antonio 193, Austin 192 and Dallas-Fort Worth 161, per 1991-2020 normals (NOAA NCEI).

How long is pool season in New York?

LaGuardia Airport (USW00014732) has 88 days at 80F, Jun 12 to Sep 7; Central Park has 81 days (1991-2020 normals, NOAA NCEI).

Why do Los Angeles and San Diego show zero days?

The LAX and San Diego Lindbergh Field normal daily highs peak at 77.4F and 78.1F, below 80F (1991-2020 normals, NOAA NCEI). Inland stations are warmer: Burbank has 120 days at 80F.

Which large metro has the shortest swim season?

Among metros with a bounded season, Buffalo has the shortest at 29 days (Jul 8 to Aug 5), per 1991-2020 normals (NOAA NCEI).

Are swim seasons getting longer?

NOAA reported that 1991-2020 normals were considerably warmer than 1981-2010 in the South and Southwest (NOAA NCEI), and 2025 was the contiguous US’s fourth-warmest year on record (NOAA NCEI). This report does not measure a trend in season length.

How does the climate season compare with DOE's pool pump season?

DOE’s 2016 state operating windows are longer than the NOAA 80F season in 59 of the 60 metros (DOE); DOE assumes year-round operation in 27 of them.

What are NOAA climate normals?

Climate normals are 30-year averages computed by NOAA NCEI every 10 years; the 1991-2020 set includes more than 7,300 stations reporting temperature (NOAA NCEI).

How was 2025 compared with the normals?

Houston’s airport logged 259 days with a high of 80F or more in 2025 vs a 1991-2020 average of 209.1, and Miami’s logged 310 vs 294.2 (NOAA NCEI GHCN-Daily).

Using and citing the index

Index figures to quote

  • Across the 60 largest US metros, the population-weighted outdoor swim season is 113.5 days a year at an 80F normal daily high (NOAA 1991-2020 normals, 2025 populations). (NOAA NCEI)
  • Miami has the longest swim season in the contiguous US among large metros: 265 days with a normal high of 80F or more, from Mar 8 to Nov 27 (NOAA 1991-2020 normals). (NOAA NCEI)
  • Buffalo’s 80F swim season lasts 29 days, from Jul 8 to Aug 5, the shortest bounded season of the 60 largest US metros (NOAA 1991-2020 normals). (NOAA NCEI)
  • Sun Belt metros average 151.2 population-weighted swim-season days a year, against 81.4 days in other large US metros (NOAA 1991-2020 normals). (NOAA NCEI)
  • Sun Belt metros took 75.9% of the population growth in the 60 largest US metros from 2020 to 2025 (Census Vintage 2025). (U.S. Census Bureau)
  • Houston’s airport logged 259 days at or above 80F in 2025, against a 1991-2020 average of 209.1 days (NOAA NCEI). (NOAA NCEI)

Underlying datasets

Index brief

A new Pool Construction & Service index measures the outdoor swim season in the 60 largest US metro areas using NOAA’s 1991-2020 climate normals. The index counts days when the normal daily high at each metro’s main airport reaches 80F. Honolulu qualifies all 365 days. In the contiguous US, Miami leads with 265 days, followed by Phoenix (232) and Orlando (227). Buffalo has the shortest bounded season at 29 days, and the airports at Los Angeles, San Diego, San Francisco and Seattle never reach an 80F normal high. Weighted by 2025 population, the average large-metro resident lives with a 113.5-day season. Sun Belt metros average 151.2 days against 81.4 elsewhere, and they took 75.9% of the 60 metros’ population growth from 2020 to 2025. The median season runs May 27 to Sep 21. Results at 75F and 85F, station IDs and all data are downloadable.

Headlines the index supports

  • Miami tops the mainland for swim season length with 265 days of 80F weather, NOAA normals show
  • Large-metro Americans get a 113.5-day outdoor swim season, new index finds
  • Sun Belt metros get 69.8 more swim days a year than the rest of big-city America
  • Buffalo's swim season lasts 29 days; four Pacific coast airports never reach an 80F normal high
  • Population shift toward the Sun Belt added 1.8 days to the average big-metro swim season since 2020

Cite the index

Pool Construction & Service. "Pool Season Length by City: Swim Season Index for 60 US Metros (NOAA 1991-2020 Normals)." PC&S Research Desk, October 4, 2026. https://poolconstructionandservice.com/research/pool-season-length-by-city/

Reuse terms

The data tables and charts in this report are licensed under CC BY 4.0. Reuse them with this attribution: “Source: Pool Construction & Service (poolconstructionandservice.com), Pool Season Length by City: Swim Season Index for 60 US Metros (NOAA 1991-2020 Normals).” Figures from third-party sources remain subject to their publishers’ terms.

Index data

Source grading

Tier 1: primary and government sources (18)

Tier 2: trade bodies, public companies, market research (3)

Tier 3: journalism and expert commentary (1)

Data sources

  1. NOAA NCEI. U.S. Climate Normals 1991-2020, daily normals station files (e.g. USW00023183.csv). Accessed 2026-10-04.
  2. NOAA NCEI. U.S. Climate Normals 1991-2020, annual/seasonal normals station files. Accessed 2026-10-04.
  3. NOAA NCEI. U.S. Climate Normals 1991-2020, monthly normals station files. Accessed 2026-10-04.
  4. NOAA NCEI. U.S. Climate Normals (product page, version 1.0.1). Accessed 2026-10-04.
  5. NOAA NCEI. Normals Calculation Methodology 2020. Accessed 2026-10-04.
  6. NOAA NCEI. Readme: By-Variable and By-Station Normals Files. Accessed 2026-10-04.
  7. NOAA NCEI. 1991-2020 normals station inventory (inventory_30yr.txt). Accessed 2026-10-04.
  8. NOAA NCEI. NOAA Delivers New U.S. Climate Normals (May 4, 2021). Accessed 2026-10-04.
  9. NOAA Climate.gov. Climate change and the 1991-2020 U.S. Climate Normals. Accessed 2026-10-04.
  10. NOAA NCEI. Global Historical Climatology Network daily (GHCNd). Accessed 2026-10-04.
  11. NOAA NCEI. Daily summaries, 2025 TMAX, Access Data Service (Phoenix shown; 7 stations). Accessed 2026-10-04.
  12. NOAA NCEI. Assessing the U.S. Temperature and Precipitation Analysis in 2025. Accessed 2026-10-04.
  13. U.S. Census Bureau. Vintage 2025 CBSA population estimates (cbsa-est2025-alldata.csv). Accessed 2026-10-04.
  14. U.S. Census Bureau. Slow Growth Impacts Nation's Largest Counties Hardest (Vintage 2025 release, March 26, 2026). Accessed 2026-10-04.
  15. National Weather Service. Cold Water Hazards and Safety. Accessed 2026-10-04.
  16. National Weather Service Baltimore/Washington. Water Safety 2018. Accessed 2026-10-04.
  17. U.S. Department of Energy. Technical Support Document: Dedicated-Purpose Pool Pumps (December 2016), Table 7.3.11. Accessed 2026-10-04.
  18. City of San Antonio Parks and Recreation. 2026 Summer Pool Season: Opens June 20. Accessed 2026-10-04.
  19. American Red Cross. Water Temperatures and ARC Aquatic Courses (Scientific Advisory Council advisory, 2018). Accessed 2026-10-04.
  20. World Aquatics. Competition Regulations (in force from June 25, 2025), rule 16.1.13.1. Accessed 2026-10-04.
  21. Pool Construction & Service. Cost to Run a Pool Pump (state DOE season table). Accessed 2026-10-04.
  22. Swim University. When To Open Your Pool in 2026. Accessed 2026-10-04.
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