Summer extreme temps warming out west and cooling in the east

[EricPeterson]

Summers are warming in the west when measured by extreme temperatures (highest temperature for the month).  Don't want average temperatures since temperatures at night are not an issue.  Can't use average temperatures anyway due to the time-of-day observation bias issue that makes it look like temperatures are dropping  when they are actually rising.  In a nutshell, the observers used to go out and set the min/max thermometer manually every day in the early evening.  But that meant that the max for the next day may in fact be the max for the current day if the next day is cooler.  Then switching to morning resets the min would be duplicated if the next day's min was warmer.  Finally switching to electronic min/max there would be no bias but unfortunately the new data would be incompatable with the old data.  So instead I simply find the max temperature for each month.   Thus the time-of-day issue is moot.
Hotter days out west are a problem, creating for example higher rates of evapotranspiration and soil moisture decrease.  That's the main reason that the average drought (which starts and ends naturally) is more severe than the average drought years ago.  Up to 4F rise per century (with a lot of natural variation) in Utah:

In the east it's a different story.  Summer extremes are dropping.  You would not know that from reading the news, but their sources are usually ASOS sensors at airports.  Those run hot especially in hot weather.  And as we know they are next to the runway.  Here's a rural Maine station with a 5F drop per century in July:

Here are all the stations I did with a link to the data and code https://virtualcoinclub.com/wx/temp/. The data came from here: https://www.ncdc.noaa.gov/cdo-web/search  I did not cherry pick any data.  I simply sorted by oldest starting date and looked for stations that continue to the present day with 98% or more data (although I prefer 99% or 100%).  The first station I found with that criteria with the list sorted by oldest starting date was the one I downloaded and plotted.

[EricPeterson]

One caveat although it was not a cherry pick  The first station I did was Kentfield CA because I wanted a long record station near the coast near one of the wine country fires.  There are undoubtedly interior CA stations that have warmed more in the summer and I will find one in the interior doing another search for CA stations.

[ChrisSmolinski]

As you know, I've previously plotted Gettysburg PA and it showed a cooling trend as well.  It also had a declining population for a period of time, which may have reduced the UHI effect?

[EricPeterson]

Yes, possibly reduced urban heat, and/or a natural cooling trend.  You have to watch for the Tobs issue if you plot averages (which doubles the problem), or highs or lows.  Or you can figure out a trick to remove that problem.  If you see a sawtooth, e.g. rise until 1970-ish, then a big drop, then a slow rise since, then you probably have a Tobs biased plot.

 I'll try to download and plot later.

[EricPeterson]

Not a lot of good station choices around Gettysburg.  I like to get 98+% coverage although I could rewrite the code a bit to accept sparse data.  But the main problem is the longest record is the 1894-2014 pumping station record.  I can try it, it might be better than nothing.

STATION NAME & ID               STARTą      ENDą   COVERAGE˛   

GETTYSBURG, PA US                1892-11-01   1982-03-31   92%

WESTMINSTER 2 SSE, MD             1893-01-01   1979-01-31   74%

TANEYTOWN, MD US GHCND:USC00188780   1893-01-01   1912-08-31   66%

FENBY, MD US GHCND:USC00183097      1893-02-01   1894-09-30   95%

BACHMAN S VALLEY, MD US         1893-10-01   1920-07-31   68%

YORK 3 SSW PUMP STATION, PA US      1894-01-01   2014-07-31   89%

HARNEY, MD US GHCND:USC00184090   1899-03-01   1907-12-31   92%

HANOVER, PA US GHCND:USC00363662   1904-04-01   1993-09-30   97%

SPRING GROVE, PA US             1932-01-01   2020-07-31   96%

YORK INDIAN ROCK DAM, PA US         1944-01-01   1946-12-31   100%

[EricPeterson]

I added winter.  Same URL: https://virtualcoinclub.com/wx/temp/  The only real surprise was how much coastal California winter  extreme temperatures have risen.   Some people might miss those temperatures in the teens just north of San Fransisco and a little inland.  But lots of plants can now survive winters that they couldn't in the past.  The downside is interior Calif (still on the todo list) where lack of bitter cold winter temps means more bark beetles survive.

In both MT and MO the coldest temperatures in Jan and Feb have moderated.  December hasn't changed as much.  In the east (ME and SC) Jan hasn't changed as much as Dec and Feb.  Not sure why the heart of winter (Jan) seems to have stayed cooler in the east but it may be an anomaly from some January Arctic blasts in the 70's and 80's.  What is not surprising is that Florida has not become less cold in winter.  In fact January has colder extremes.  A lot of that trend is from just a few incredible Arctic blasts in the early 80's and 1985 that basically finished off the orange trees in Orange county.

The bottom line though, is that global warming is stronger in winter.