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.

[Mike Cycle]

An updated version of BEST is available, write up is here:  https://essd.copernicus.org/preprints/essd-2026-412/

Berkeley Earth Surface Temperature – High-Resolution (BEST-HR): a 0.25° Global Gridded Temperature Data Set for Climate Monitoring

Robert A. Rohde, Bruce Calvert, and Zeke Hausfather

Abstract. We present version 2 of the Berkeley Earth Surface Temperature dataset, a global observational temperature record that now features enhanced spatial resolution (0.25° × 0.25°) and a new regression Kriging framework that incorporates physically informed predictive fields. The land analysis uses 58,311 weather stations, updated to reflect the latest source archives, and includes separate reconstructions for TAVG (1750–present), TMAX, and TMIN (both 1850–present). Sea surface temperatures are derived from HadSST4, with spatial detail improved using predictors from the ORAS5 ocean reanalysis. The land and ocean fields are merged into a unified product with a refined coastal blending method. A new uncertainty ensemble is introduced to quantify reconstruction and coverage uncertainty, enabling propagation of errors into derived metrics. The resulting Berkeley Earth Surface Temperature – High-Resolution (BEST-HR) dataset offers a globally complete, monthly resolved temperature product suitable for applications ranging from global trend analysis to regional climate impact assessments. The current BEST-HR dataset described in this paper has been archived at Zenodo DOI: 10.5281/zenodo.20428381 alongside the merged weather station data used to generate it DOI: 10.5281/zenodo.20427092. Monthly updates to these datasets will be provided primarily through the Berkeley Earth website.

[chubbs]

4 hours ago, Mike Cycle said:

An updated version of BEST is available, write up is here:  https://essd.copernicus.org/preprints/essd-2026-412/

Berkeley Earth Surface Temperature – High-Resolution (BEST-HR): a 0.25° Global Gridded Temperature Data Set for Climate Monitoring

Robert A. Rohde, Bruce Calvert, and Zeke Hausfather

Abstract. We present version 2 of the Berkeley Earth Surface Temperature dataset, a global observational temperature record that now features enhanced spatial resolution (0.25° × 0.25°) and a new regression Kriging framework that incorporates physically informed predictive fields. The land analysis uses 58,311 weather stations, updated to reflect the latest source archives, and includes separate reconstructions for TAVG (1750–present), TMAX, and TMIN (both 1850–present). Sea surface temperatures are derived from HadSST4, with spatial detail improved using predictors from the ORAS5 ocean reanalysis. The land and ocean fields are merged into a unified product with a refined coastal blending method. A new uncertainty ensemble is introduced to quantify reconstruction and coverage uncertainty, enabling propagation of errors into derived metrics. The resulting Berkeley Earth Surface Temperature – High-Resolution (BEST-HR) dataset offers a globally complete, monthly resolved temperature product suitable for applications ranging from global trend analysis to regional climate impact assessments. The current BEST-HR dataset described in this paper has been archived at Zenodo DOI: 10.5281/zenodo.20428381 alongside the merged weather station data used to generate it DOI: 10.5281/zenodo.20427092. Monthly updates to these datasets will be provided primarily through the Berkeley Earth website.

Here's warming since 1850 for the Mid-Atlantic in the new Berkeley dataset. Chester County has similar warming to the region as a whole. The Berkeley warming in good agreement with NCEI, and other groups.

https://dashboard.theclimatebrink.com/#map

 

[ChescoWx]

Hello all. Announcing something new on chescowx.com...ChescoWx Studies! This is an ongoing series looking at what makes Chester County's climate unique, this will include deep analysis of climate patterns and cycles, weather monitoring equipment and tools and past storm write ups and details. Each study takes one question, tests it against our station records and gives you the answer with the numbers behind it. I would welcome any feedback or pushback on the methods or the results.

The series lives here and will grow as new studies are finished:
https://chescowx.com/chescowx-studies/

Study 1 - Equipment & Siting. Three stations at my place in East Nantmeal. A ground-level fan-aspirated Davis, a rooftop Tempest and a ground-level Ambient with a passive shield. The Tempest highs ran about +3°F in July through September and +3.3°F on sunny, calm days, with 45 days of 90°F vs 8 for the Davis. To separate the roof from the shield, I looked at the Ambient. From 2021 to 2023 its summer highs matched the Davis within a few tenths while the Tempest was +2.8°F...so it is the roof, not the shield. Once the Ambient shield was damaged, though, it ran almost 7°F warm on sunny days. Location first, then upkeep.

Study 2 - Elevation & Terrain. Most of our hilltop stations came along decades after the valley ones, and the weather varies from one decade to the next, so I compared them over the same years (2012 to 2025) using USGS 3DEP elevations. 19 stations with at least 8 complete years, by band:

100 to 300 ft (4 stations): high 64.4, low 43.6, 90 degree days 19, freezing nights 111, growing season 182 days
300 to 600 ft (8 stations): high 63.3, low 44.5, 90 degree days 11, freezing nights 101, growing season 192 days
600 ft and up (7 stations): high 62.3, low 45.3, 90 degree days 9, freezing nights 94, growing season 204 days

Days follow elevation and nights follow terrain position. Highs drop about 1.7°F for every 300 ft, but lows track how far a station sits above its immediate surroundings, which is why they actually rise as you go up.

For snow I used a same-storm comparison (521 storms, 60+ human-observed sites) so a snowy decade at one station does not skew it. Overall the hills get about 8% more snow for every 300 ft (29% per 1,000 ft), but the time of season matters a lot:

Oct-Nov (24 storms) about 25% per 300 ft
Dec-Jan (251 storms) about 6%
Feb (151 storms) about 5%
Mar-Apr (95 storms) about 18%

March 2004 is a good example: East Nantmeal 11.0, Coatesville 2W 8.8 vs Exton 3.0, Chadds Ford 3.4, West Chester 2.2. There are always a few sites that do not fit, and the southern uplands around West Grove and New London run less than their elevation would suggest. The north also gets a bit more than the south, while the western part of the county gets more only because it is higher. Precipitation showed no elevation effect at all.

Let me know if any questions, if you see anything that does not hold up, or if there is a question you would like to see tested next!