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

[ChescoWx]

Below is the summer (June-July-August) temperature summary for 2026 and summer temperature history from 1871-1926. This was 33rd warmest summer but overall since 1895 there has been no statistically significant warming or cooling across both the raw and composite trend and only the NCEI adjusted averages indicate any significant summer warming.

[Mike Cycle]

Paul, I started looking at the difference between the daily nclimgrid and daily raw station data for Chester County and surrounding area for 1951 forward.  Daily data for nclimgrid starts at 1951. A sample of that analysis is attached, showing that the difference varies by station.  This is interesting.  The difference may be amenable to modeling.

Cell size for the nclimgrid is about 2 X 2 miles--the red squares are each a cell with a time series.  When looking at CAG, we are seeing an average for the county of these squares.  

Can you provide the station list for your recent analysis?

Edit.  Some of the difference may correlate with nearby forest ET, and some may correlate with site geomorphology.

[Bhs1975]

Below is the summer (June-July-August) temperature summary for 2026 and summer temperature history from 1871-1926. This was 33rd warmest summer but overall since 1895 there has been no statistically significant warming or cooling across both the raw and composite trend and only the NCEI adjusted averages indicate any significant summer warming.

Looks like we should all move to Chester County to escape the inferno.


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[ChescoWx]

21 hours ago, Bhs1975 said:

Looks like we should all move to Chester County to escape the inferno.


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And also to avoid the burning oceans correct?? LOL!!! Oh the humanity!!!!

[ChescoWx]

On 9/1/2026 at 4:35 PM, Mike Cycle said:

Paul, I started looking at the difference between the daily nclimgrid and daily raw station data for Chester County and surrounding area for 1951 forward.  Daily data for nclimgrid starts at 1951. A sample of that analysis is attached, showing that the difference varies by station.  This is interesting.  The difference may be amenable to modeling.

Cell size for the nclimgrid is about 2 X 2 miles--the red squares are each a cell with a time series.  When looking at CAG, we are seeing an average for the county of these squares.  

Can you provide the station list for your recent analysis?

Edit.  Some of the difference may correlate with nearby forest ET, and some may correlate with site geomorphology.

Hi Mike, as luck would have it I just soft launched my updated website we now have all sorts of interactive opportunities etc. along with all of the source data. Check it out at www.chescowx.com    let me know if you need any other data or if you have suggestions or adds as I am building more utility through the site. Thanks!

[ChescoWx]

Hello all. The ChescoWx website https://chescowx.com has had a major overhaul and it is now live!

Everything is interactive now. You can pull up climate trends unique to the Philly burbs of Chester County PA for any measure, look at a single station or the whole county, and compare us against Philadelphia, Reading, or Allentown airports. There are all time records, decade summaries and climate trending options going back to the 1870's, top snowstorms, snow by season and even a White Christmas history.

Every trend also tells you whether that trend is statistically significant or simply weather noise. Behind the enhanced website sits 42 Chester County area stations and more than 458,000 daily observations going back to 1871.

Take a look and let me know what you think and what we are missing you would like to see or be able to view interactively. Thanks! Paul

[Mike Cycle]

Paul, your site functionality is impressive.  This must have taken a lot of work to get it all running, even with AI writing code.  

TBH, though, we are still not agreeing on the use of raw weather data to develop climate trends, although at really large scales there is little difference between the raw and processed.  --Mike

edit:  I see and appreciate the steps you have taken to improve the averaging process you are using, "Instead a level offset is solved for each station...".  This to some extent mitigates the changing station locations over time, based on their official names, but I note that this still does not incorporate the information we have about station moves within a given station name, such as those for Coatesville.  

 

[ChescoWx]

On 9/9/2026 at 11:39 AM, Mike Cycle said:

Paul, your site functionality is impressive.  This must have taken a lot of work to get it all running, even with AI writing code.  

TBH, though, we are still not agreeing on the use of raw weather data to develop climate trends, although at really large scales there is little difference between the raw and processed.  --Mike

edit:  I see and appreciate the steps you have taken to improve the averaging process you are using, "Instead a level offset is solved for each station...".  This to some extent mitigates the changing station locations over time, based on their official names, but I note that this still does not incorporate the information we have about station moves within a given station name, such as those for Coatesville.  

 

Thanks Mike!!

[ChescoWx]

Below is a snapshot of both the raw actual annual average temperatures and the NCEI adjusted for Chester County PA over the last 10 years from 2016-2025. Both trend lines show a cooling period is underway but neither line is statistically significant. Could this indeed be the start of our next cooling cycle in our never ending cycle of climate change?

[Mike Cycle]

There is significant difference between the nClimGrid annual Tavg that can be downloaded at Climate at a Glance, and the individual cells that make up the nClimGrid and that are averaged to make the Chester County data at CAAG. An example is provided below.  What this means is that comparing raw data from a station list that changes over the years to a stable average from nClimGrid that always includes all cells will allow the raw data to incorporate shifts in lat/lon, but not the adjusted data.  I have not had time to do the work yet, but what needs doing is to make time series from the nClimGrid cells that matches the raw data dates and locations.  Since this thread is "battle-of-actual-vs-altered-climate-data".  Another step would be to find the average elevation of each cell, and use the station elevation to apply a lapse rate to the nClimGrid cell data.

Here is a comparison of Phoenixville raw (complete years only) to the nClimGrid cell data.  Also, a closer look at the Phoenixville raw data sheets might shed some light on how Phoenixville collected the state's record for high temp.

[chubbs]

12 hours ago, Mike Cycle said:

There is significant difference between the nClimGrid annual Tavg that can be downloaded at Climate at a Glance, and the individual cells that make up the nClimGrid and that are averaged to make the Chester County data at CAAG. An example is provided below.  What this means is that comparing raw data from a station list that changes over the years to a stable average from nClimGrid that always includes all cells will allow the raw data to incorporate shifts in lat/lon, but not the adjusted data.  I have not had time to do the work yet, but what needs doing is to make time series from the nClimGrid cells that matches the raw data dates and locations.  Since this thread is "battle-of-actual-vs-altered-climate-data".  Another step would be to find the average elevation of each cell, and use the station elevation to apply a lapse rate to the nClimGrid cell data.

Here is a comparison of Phoenixville raw (complete years only) to the nClimGrid cell data.  Also, a closer look at the Phoenixville raw data sheets might shed some light on how Phoenixville collected the state's record for high temp.

Why Phoenixville has the state record is covered in this thread. Phoenixville ran much warmer than other local stations on summer afternoons between the mid-1920s and the 1948 move. Probably due to a shelter that didn't provide adequate sun shielding. The spike in 90F days in the 30s and 40s shows the time period when Phoenixville ran warm.  In the month when the state record was set, July 1936, high temperatures were 6-7F higher in Phoenixville than other local stations.  Another reason why the raw data in Chester County requires bias adjustment.