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

[ChescoWx]

So let's go ahead and use the adjusted NCEI average annual temperatures for Chester County PA from NCEI this century. These are the adjusted altered figures Charlie....what does this tell us?  Even after adjustments by NOAA PHL is indeed warming almost 70% faster than Chester County PA - the PHL UHI is a problem even NOAA shows it....

[chubbs]

20 hours ago, ChescoWx said:

Bad assumption only using the warmest station which is Phoenixville 1E - to better determine the true Chesco average you should add in the nice mix we have today of high and low elevations to capture the true average Chester County average temperature. Heck the averages I derive from these stations is in reality supports almost exactly the calculated average temperatures posted by NCEI on their site for their recent Chester County PA average temperatures. If NCEI develops an average temperature for the county that is statistically the same as what I calculate from the raw stations. See below since 2004. NCEI must think the mix of stations I use is strong correct? 

I have no problem with your current set of stations. As you say it provides good coverage and matches NCEI. The problem isn't the current stations, its the difference between the current stations and the older stations. There isn't a single current station in the county that is as warm as any of the 3 county stations in 1945. You can't get our climate history right without properly accounting for the changes in county stations with time. Note also that consistency is much more important than coverage when tracking long term changes in temperature. 

[chubbs]

On 5/22/2026 at 12:42 PM, ChescoWx said:

So let's go ahead and use the adjusted NCEI average annual temperatures for Chester County PA from NCEI this century. These are the adjusted altered figures Charlie....what does this tell us?  Even after adjustments by NOAA PHL is indeed warming almost 70% faster than Chester County PA - the PHL UHI is a problem even NOAA shows it....

The difference in slope is not statistically significant. That said, wouldn't be surprised if PHL had a some warming enhancement from UHI; but, based on comparisons to other sites it is small compared to the region-wide warming in recent decades. More data is needed to make the case though. Note that the Avondale USHCRN station has a higher slope than PHL. Are you saying that the warming there is due to UHI?

[ChescoWx]

No matter how you slice it using either the raw or altered adjusted data. The gap is clearly widening between PHL and Chester County

[chubbs]

17 hours ago, ChescoWx said:

No matter how you slice it using either the raw or altered adjusted data. The gap is clearly widening between PHL and Chester County

But it does matter how you slice it; and, you continue to cherry pick favorable comparisons and ignore the rest. I stated above that the slope difference between NCEI and PHL between 2000 and 2025 was not statistically different. Expanding the yaxis doesn't change that result.

Looking over a longer period and re-normalizing the yaxis, we see that the delta between Chester County and the Philadelphia Airport has stayed the same since 1970. The delta goes up and down but without a long-term trend; 2000 just happens to be a minimum. Doesn't matter whether you use NCEI or high quality sites like Coatesville, Avondale USCRN, and DEOS. The answer is the same. 

 

[ChescoWx]

3 hours ago, chubbs said:

But it does matter how you slice it; and, you continue to cherry pick favorable comparisons and ignore the rest. I stated above that the slope difference between NCEI and PHL between 2000 and 2025 was not statistically different. Expanding the yaxis doesn't change that result.

Looking over a longer period and re-normalizing the yaxis, we see that the delta between Chester County and the Philadelphia Airport has stayed the same since 1970. The delta goes up and down but without a long-term trend; 2000 just happens to be a minimum. Doesn't matter whether you use NCEI or high quality sites like Coatesville, Avondale USCRN, and DEOS. The answer is the same. 

 

But again the facts remain - either way we look at the data both raw and altered still shows a widening gap since 1970 - no reason to think that gap will not continue to widen. 

[rygar]

this thread is like an Alexa vs Google Home conversation

[chubbs]

On 5/25/2026 at 9:40 AM, ChescoWx said:

But again the facts remain - either way we look at the data both raw and altered still shows a widening gap since 1970 - no reason to think that gap will not continue to widen. 

Your "raw data" doesn't look like the raw data for individual stations that I posted upthread. Why? The station population that you are averaging is cooling with time which distorts the data. Here is a plot of Chester County stations minus Coatesville, the most stable station between 1970 and 2025. Positive values indicate that the station is warmer than Coatesville, negative cooler.

The station population cools you are using with time. Over 55 years Coatesville goes from being the warmest station to an average station. The 19 station average warms by 1.5F between 1970 and 2025. That is larger than the "raw data" increase for PHL shown in your chart. Indicating that the positive slope in your chart is due solely to the change in station population. Reposting my table which shows that the raw data from individual stations doesn't show any difference in warming between Chester County and PHL. When you factor in the bias from the changing station population, your analysis agrees with mine. 

[ChescoWx]

2 hours ago, chubbs said:

Your "raw data" doesn't look like the raw data for individual stations that I posted upthread. Why? The station population that you are averaging is cooling with time which distorts the data. Here is a plot of Chester County stations minus Coatesville, the most stable station between 1970 and 2025. Positive values indicate that the station is warmer than Coatesville, negative cooler.

The station population cools you are using with time. Over 55 years Coatesville goes from being the warmest station to an average station. The 19 station average warms by 1.5F between 1970 and 2025. That is larger than the "raw data" increase for PHL shown in your chart. Indicating that the positive slope in your chart is due solely to the change in station population. Reposting my table which shows that the raw data from individual stations doesn't show any difference in warming between Chester County and PHL. When you factor in the bias from the changing station population, your analysis agrees with mine. 

Inventing and mixing and matching  data I see - Coatesville is not the most stable station for those 55 years....heck they only have 13 years at 1SW and 25 years at another location 2W. That only adds up to 38 years over a 55 year span. There has been no Coatesville COOP data for the last 20 years!! 

[forkyfork]

why does chester county matter so much

[ChescoWx]

5 minutes ago, forkyfork said:

why does chester county matter so much

Because it is where I live....LOL!

[chubbs]

3 hours ago, ChescoWx said:

Inventing and mixing and matching  data I see - Coatesville is not the most stable station for those 55 years....heck they only have 13 years at 1SW and 25 years at another location 2W. That only adds up to 38 years over a 55 year span. There has been no Coatesville COOP data for the last 20 years!! 

I knew you would find some reason to dismiss.  My stability assessment is based on comparing Coatesville to NCEI and other regional stations without station changes. Coatesville tracks NCEI closely. Yes there are three stations; but, the three stations are well matched for annual average temperatures; and, there are no major station changes. You would get the same answer if you used NCEI instead of Coatesville.

 

[Cobalt]

Do we have equal right to open up a thread for each of the other 3142 counties in the US?

[Santa Claus]

imagining the managing director of a multibillion dollar catastrophe bond fund at a reinsurance house making trades based on the weather station at scumhill road in chester county pennsylvania

[ChescoWx]

13 hours ago, Cobalt said:

Do we have equal right to open up a thread for each of the other 3142 counties in the US?

Please do Cobalt that would be great! Thanks!!

[ChescoWx]

As we get into the summer months lower elevation (<450 ft asl) areas of Chester County PA will see at least one heat wave (defined as 3 or more consecutive days with highs at 90 degrees or above) while the relatively higher ridge locations (>600 ft asl) only average a heat wave every couple of years or so. Below sorted by highest to lowest elevation is a ranking of all reporting stations since 2000 with their recorded heat waves. Our lowest elevation spot at Phoenixville averages a whopping two to four times the number of heat waves as almost all other locations across the county.

[ChescoWx]

Even the longest running continuous and warmest station in Chester County at Phoenixville has a clear trend toward less of the so called "heat waves" 

[ChescoWx]

On 5/29/2026 at 1:29 PM, chubbs said:

I knew you would find some reason to dismiss.  My stability assessment is based on comparing Coatesville to NCEI and other regional stations without station changes. Coatesville tracks NCEI closely. Yes there are three stations; but, the three stations are well matched for annual average temperatures; and, there are no major station changes. You would get the same answer if you used NCEI instead of Coatesville.

 

Welp except for what you have stated before were the multiple moves from a relatively more urban locale to rural at Coatesville 1SW and of course the increase in elevation with the 1983 move to Coatesville 2W and then over to KMQS.......

[ChescoWx]

Maybe an even better example of the Urban Heat Island Problem at PHL Airport is to compare the airport to NWS COOP observations at Octoraro Lake on the SW border of Chester County at about 40 nautical miles due west of the airport. Octoraro Lake is a relative low elevation spot (260 ft asl) and that NWS COOP station is clearly seeing decreasing heat waves while PHL continues to have increasing "heat waves". The only material difference is rural vs UHI