Monday, May 29, 2017

U.S. Daily Record Highs Outnumber Lows 5 to 1 since 2010

Christopher C. Burt · May 29, 2017

As detailed in the caption above, Galveston, Texas, has set an amazing number of heat records in the last few years. Blogger Matt Lanza (@mattlanza) recently wondered if any other city in the U.S. has broken so many heat records in the same span of time (since 2010). I decided to follow that line of inquiry and researched 60 cities in the contiguous U.S. that have National Weather Service NOWData online records going back to at least 1895. In addition, I looked at six sites in Alaska and Hawaii as well, although only two (Juneau and Honolulu) have periods of record (PORs) dating back to 1895.


After choosing these sites, I used the option in NOWData’s local search tool to search from January 1895 through April 2017 for daily temperature records set on each day of the year:

Tmax: highest temperature recorded on this date
Tmax/Min: highest minimum temperature recorded on this date (typically the warmest nighttime reading)
Tmin: lowest temperature recorded on this date
Tmin/Max: lowest maximum temperature recorded on this date (typically the coldest daytime reading)

Thus, four parameters for daily record temperatures were chosen for this report.



• Not a single site recorded more daily cold records than warm ones. Eureka, California came the closest with a heat-over-cold ratio of just 1.18 to 1.00, and Reno, Nevada had the greatest ratio with 24.13 to 1.00 warm records over cold records. The ratio at Reno was much larger than for any other station in my dataset from the contiguous U.S. Barrow, Alaska’s ratio was an astonishing 66.00 to 1.00, although its POR did not begin until 1921. I discussed the increasing warmth at Barrow in a Category 6 post in April.

• The average ratio of warm records over cold records for all 60 contiguous U.S. sites was 4.89 to 1.00 for the period of 2010 to 2017.

• Record warm nights (i.e. Tmax/Mins) were 29.5% more prevalent than record warm days (Tmaxs) and record cold days (Tmin/Maxs) were 22.2% more prevalent than record cold nights (Tmins).

• There was no indication that one region of the U.S. set more temperature records (either warm or cold) than any other region.

• A few sites had not recorded a single daily Tmin (coldest daily minimum) record since 2010. These included Reno, where the last Tmin record was set in 2004; Phoenix (last daily Tmin set in 2008); and Barrow (last daily Tmin set in 2007).

• Tampa, Florida recorded the most daily warm records (Tmax or Tmax/min) of any site researched with, 210 such days. This is just short of Galveston’s 216, so Matt Lanza may be correct in his hypothesis that Galveston has measured more daily heat records than any other first-order NWS site in the U.S. with a POR going back to at least 1895.


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