Chester County PA - Analytical Battle of Actual vs. Altered Climate Data

[ChescoWx]

Wonder what is going on at KRDG since 2021?? Further north higher elevation than Phoenixville but now warmer than the Chesco warm spot.

[ChescoWx]

There are some who believe our nightime lows are getting warmer during the summer months. The actual data sees no such warming - almost flat since 1893!

[TheClimateChanger]

5 hours ago, ChescoWx said:

I love when climate zealots simply eliminate stations they deem absurd....LOL!

This is especially ironic coming from someone who normally claims NOAA’s modern records are bogus, adjusted, contaminated, or otherwise untrustworthy. But a lone 105°F reading from a high-elevation northern interior New York site in 1919, with surrounding stations reporting 88–94°F on the same date, is suddenly sacred scripture? And that was literally the only substantive change I made. The rest of the map is from Martz’s own website, just reassembled to show the most recent occurrence of a given high, with a couple of corrections for omissions (Maryland & NC in 2012) and updated to include 2025's record highs(map ends in 2024). Martz himself excludes 

[chubbs]

14 hours ago, TheClimateChanger said:

This is especially ironic coming from someone who normally claims NOAA’s modern records are bogus, adjusted, contaminated, or otherwise untrustworthy. But a lone 105°F reading from a high-elevation northern interior New York site in 1919, with surrounding stations reporting 88–94°F on the same date, is suddenly sacred scripture? And that was literally the only substantive change I made. The rest of the map is from Martz’s own website, just reassembled to show the most recent occurrence of a given high, with a couple of corrections for omissions (Maryland & NC in 2012) and updated to include 2025's record highs(map ends in 2024). Martz himself excludes 

The deep dive in Chester County has made me very suspicious of older high temperature records in the US. Non-aspirated thermometers used back in the day are sensitive to shelter placement. It only takes one poorly sited station on one day to make a max temperature statistic misleading. Phoenixville in Chester County is a good example. Much hotter max temperatures than surrounding stations for 20 years in the 1930s and 40s. Well documented in this thread.  As you show above, Martz's chart of nationwide high temperature records has the same problem. This whole thread is about using inconsistent data past vs present, to present misleading information.

[ChescoWx]

Many folks have asked for an analysis of both the Average Summer High temperature and Overall Average Temperature trends specifically for Chester County PA.

Clearly steady state since 1893!

[ChescoWx]

Are we already in our next cooling climate cycle for summer? Since 2010 summers now show a cooling trend!

[Santa Claus]

yeah it’s freezing out there

[Santa Claus]

“my stomach shows a shrinking trend” i explain to my doctor who is mildly concerned that i brought a sack of hamburgers to my appointment

[ChescoWx]

So I asked AI who is the best source of weather / climate data for Chester County PA? Can AI be wrong??

[ChescoWx]

Here in Chester County PA most spots have seen an above normal amount of 90+ days so far this season. Below are the number so far this season by station along with the average per typical season along with the most and least by station. You can clearly see how relative elevation across our area impacts the number of such days. Also below you can see our average annual number of 90+ days is showing a clear reduction in number as we compare past decades to the 2020's.

[rygar]

On 6/13/2026 at 11:08 AM, ChescoWx said:

So I asked AI who is the best source of weather / climate data for Chester County PA? Can AI be wrong??

I asked AI for a realistic and true temperature graph for Chester County PA, covering the last 100 years

[ChescoWx]

24 minutes ago, rygar said:

I asked AI for a realistic and true temperature graph for Chester County PA, covering the last 100 years

Sure after chilling adjustments made to the past for 90 consecutive years across Chester County......below is the realistic and actual temperature graph covering the last 100 years....no climate crisis here without those consistent post hoc alterations to the actual real data! Still trying to get as warm as the old days back in the 1930's and 1940's!

[ChescoWx]

With a chance that some locations could see a 100-degree day later this week I went back and analyzed 30 temperature stations across the area to see just how rare such a day has become. A 100-degree day is a rare occurrence across most spots across the County. With the potential being even more rare across the relatively higher ridge stations above 595 ft. In fact the last time any ridge location station saw a 100-degree reading was 15 years ago back on July 22, 2011. Of the 18 current stations across the area that report temperatures 9 of these have never recorded such a day. Our lowest elevation stations at Phoenixville and nearby Spring City both recorded a 100+ day last June. To illustrate how different the temperature elevation impact can be on June 26, 2025 while Spring City (256 ft ASL) was hitting the century mark....not too far away at Glenmoore DEOS (620 FT ASL) but 400 feet higher the high was 10 degrees cooler at "only" 90.6

[ChescoWx]

Below is the June and 1st Half of 2026 Chester County Area Climate Summary. Overall the county finished with a slightly above average temperature of 70.8 degrees or 0.6 degrees above the 1991-2020 climate baseline for June of 70.2 degrees. When using the entire climate dataset since 1893 we finished only +0.4 degrees above our overall 134 year average June temperature which is 70.4. This was 1.2 degrees cooler than June 2025 and our coolest June since the 67.4 degree average in June 2023. This was our 61st warmest June over the last 134 years of county climate data. Through the 1st 6 months of the year our average temperature was 48.0 degrees. This is 0.4 degrees below the 1991-2020 baseline and 0.1 degree over the 1893 - 2025 baseline. This represents our coldest start to a year since 2015. Overall this is the 66th warmest 1st half of a year over the last 134 years. Average precipitation across all stations was 3.11" this is 1.20" the 1991-2020 baseline and 1.02" below the overall average since 1893. For the 1st half of the year county precipitation has averaged 15.34" this is 6.95" below the 1991-2020 baseline of 22.29" and 6.82" below the 1893-2026 all years average of 22.16". This is our 7th driest average precipitation total with the lowest being the 13.82" average for the first half of 1963.