Understanding extreme weather patterns: What NOAA's day counts and the records say about heat and cold
Extremes sit at the edge of the normal: the days a year that reach 90°F, the nights that freeze, the records. Among U.S. places of 50,000 or more, Laredo, TX has the most 90°F days (185 a year) and Flagstaff, AZ the most freezing nights (202). Since 2010 large cities have set 25% of their monthly record highs and 2% of their record lows.
First published · revised
Counting hot days and cold nights
NOAA's normals count, for every station, the days in a typical year above thresholds: highs of 90°F and 100°F, lows of 32°F and 0°F, days that stay below freezing. Those counts describe how often extremes come, which a monthly average hides. The most 90°F days among large places: Laredo, TX (185), Indio, CA (184), Casa Grande, AZ (184), Maricopa, AZ (183) and Yuma, AZ (181). The most freezing nights: Flagstaff, AZ (202), Bozeman, MT (198), Anchorage, AK (186), Grand Forks, ND (185) and Bismarck, ND (184).
Records
A record is the single highest or lowest reading on the station's history. PlainClimate shows a record only from at least 20 complete years and only when it is plausible against the station's own normals; a month whose reading fails that check is left out rather than corrected.
When were the big cities' records set?
The National Weather Service keeps one long "threaded" record for each large city, joining the stations that kept its weather over time. Across the 141 threaded records of U.S. places of 100,000 or more, 424 of the 1,691 monthly record highs (25%) were set in 2010 or later, against 39 of the 1,692 monthly record lows (2%). Before 1950 the balance ran the other way for lows: 50% of the record lows date from then, and 38% of the record highs. Records count once per month per city, so a decade's share is a share of 12 monthly records at each city.
| Decade | Record highs | Record lows |
|---|---|---|
| 1840s | 0 | 3 |
| 1850s | 0 | 1 |
| 1860s | 0 | 11 |
| 1870s | 11 | 34 |
| 1880s | 17 | 84 |
| 1890s | 53 | 146 |
| 1900s | 74 | 97 |
| 1910s | 115 | 134 |
| 1920s | 96 | 95 |
| 1930s | 188 | 92 |
| 1940s | 93 | 150 |
| 1950s | 149 | 137 |
| 1960s | 65 | 217 |
| 1970s | 68 | 147 |
| 1980s | 153 | 215 |
| 1990s | 92 | 64 |
| 2000s | 93 | 26 |
| 2010s | 216 | 30 |
| 2020s | 208 | 9 |
Older records had more years to be broken and the threads begin in different years (the earliest in the 1840s), so the count by decade is not a rate; the contrast between highs and lows in the same decades is the finding. A tied record keeps the latest date ACIS reports.
What these do not include
Tornadoes, hurricanes, hail and floods are events, not normals; NOAA's Storm Events Database records them county by county.
Source: NOAA NCEI 1991-2020 normals (day counts); records: ACIS, NWS threaded city records.