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

[chubbs]

19 hours ago, Mike Cycle said:

Hi All, occasional lurker and Chester County resident here.   

I have done a deep dive on Coatesville 1 SW's history, working through the 530-1, the monthly paper records and property deeds for observers Gordon, Pyle and PECO.  I then compared the record of station changes with the breakpoints identified by NOAA/NCEI and Berkeley Earth Surface Temperature (BEST).  Claude helped with the graphic.

There is remarkable agreement between the history of changes at 1 SW and the breakpoints detected.   

edit:  The HOMR record for this station, (presumably pulled from the 1956 530-1 (itself likely pulled from the B44s)) is flawed.  

Very interesting. More evidence supporting bias adjustment in Chester County. The detailed documentation describes many more station changes than the NCDC documented. Indicates that the move from the City of Coatesville to Doe Run Road occurred in 1946. Per NCDC documentation Doe Run road site wasn't used until 1949.

[Mike Cycle]

Observer Pyle made a remark about the station move on the January 1946 record.  Then there is a record gap through to October 1948, when the first PECO observation record appears.  I don't know if this is a real gap.

During the same time, observer Pyle is also taking stream gage measurements.  

The earliest address is shown as 547 E. Main, across from the high school, but observer Gordon owned 574 E. Main, and there is no 547 E. Main on current mapping.  https://arcweb.chesco.org/LR_INFO/lr_info.aspx?PARID=1606 03640000

 

[chubbs]

1 hour ago, Mike Cycle said:

Observer Pyle made a remark about the station move on the January 1946 record.  Then there is a record gap through to October 1948, when the first PECO observation record appears.  I don't know if this is a real gap.

During the same time, observer Pyle is also taking stream gage measurements.  

The earliest address is shown as 547 E. Main, across from the high school, but observer Gordon owned 574 E. Main, and there is no 547 E. Main on current mapping.  https://arcweb.chesco.org/LR_INFO/lr_info.aspx?PARID=1606 03640000

 

The bulk of the post-war Coatesville cooling occurred in 1946 and 1947 which is consistent with a 1946 move. The cooling relative to West Chester and ABE also matches the timing and roughly 2F magnitude of the NCEI and Berkeley Earth bias adjustments that you posted above.

[Mike Cycle]

The 1946 station move looks like a train switching from one track to another. Nice. 

Here is a view of surface temperatures from NASA's ECOSTRESS instrument on the space station.  Coatesville 1 SW generally moves progressively from hotter to colder microclimates.

 

[forkyfork]

all this posting about some podunk hellhole where people trade their babies for percocet 

[rclab]

3 hours ago, forkyfork said:

all this posting about some podunk hellhole where people trade their babies for percocet 

Well there goes your shot for the congeniality award at the atmospherics convention. As always …..

[ChescoWx]

On 8/3/2026 at 6:48 AM, Mike Cycle said:

Observer Pyle made a remark about the station move on the January 1946 record.  Then there is a record gap through to October 1948, when the first PECO observation record appears.  I don't know if this is a real gap.

During the same time, observer Pyle is also taking stream gage measurements.  

The earliest address is shown as 547 E. Main, across from the high school, but observer Gordon owned 574 E. Main, and there is no 547 E. Main on current mapping.  https://arcweb.chesco.org/LR_INFO/lr_info.aspx?PARID=1606 03640000

 

 

 

 

 

Thanks for the great info @Mike Cyclebut the statistical analysis showed us that there were no unusual temperature changes at Coatesville 1SW that were not statistically aligned with the nearby stations within 30 miles of that point to support. This supports the fact that there was no need for any adjustments to the raw data at all!

[Mike Cycle]

Chesco, you are quite welcome.  Seems like an important step towards understanding the data adjustments done by NCEI and BEST, and the topic of this forum..

The next step is to look at how break points are identified using reference stations.  Chubbs has a graph above showing the 1946 break resulting from 1 SW's move to Newlinville, and here is similar graph also using raw data.  What I have done is synchronize the temperature series at 1945, and removed the absolute temperature values on the Y-axis--because the absolute values don't matter if we are looking for climate trends.  This shows just the 1946 break, and shows the RESULT/IMPACT the station move made on Tavg. Now, imagine repeating this process with a large set of reference stations across the whole history of 1 SW to create a time line of breaks and the deg F size of the shift at each break. That is what is done.  With the new information from the breaks, we can adjust the station data by reversing the IMPACT of the moves.  With the repaired data set, we can then identify baselines and departures from those baselines--anomalies.  Absolute values don't matter, the change over time does.   

Also, by convention the adjustments are made with the end of the raw data series aligned to the same temperature as the end of the adjusted data series.  This may lead to confusion when the raw and the adjusted data are viewed in the same graph, because it looks like one series has been "chilled" or "warmed" with respect to the other.  The reality is that the raw data for Coatesville is actually several distinct stations, and the adjusted data has been upgraded to be a lot closer to what the raw data would have looked like if the station never moved.  Trying to assign absolute temperatures to either time series is not useful when the information we want is change over time. 

With that in mind, would you clarify what you mean by  "there were no unusual temperature changes at Coatesville 1SW that were not statistically aligned with the nearby stations within 30 miles of that point" & "This supports the fact that there was no need for any adjustments to the raw data at all!"?  

 

[Mike Cycle]

Here is a graphic I hope illustrates that the goal of homogenization is not to create a new absolute temperature series for a given location, but to extract change over time information.  With Coatesville 1 SW, because it moved to progressively cooler locations (break points finds these shifts), it is necessary to correct for those moves.  Convention is to apply the corrections from most recent raw data backwards, but it is just as valid to apply them from oldest forward. Convention results in a repaired series that was always in its final location, and applying corrections from oldest forward results in a station that never left its first location.     

[chubbs]

When you focus on periods just before and just after station changes, the changes are have very strong statistical significance. Below is an example for Coatesville, using the monthly difference between Coatesville and West Chester.  On average, Coatesville was 2.5F cooler relative to West Chester in 1949-50 vs 1944-45, before the 1946 move. The stats show that the move-related change was highly significant statistically. 

 

[ChescoWx]

On 8/4/2026 at 10:52 PM, Mike Cycle said:

With that in mind, would you clarify what you mean by  "there were no unusual temperature changes at Coatesville 1SW that were not statistically aligned with the nearby stations within 30 miles of that point" & "This supports the fact that there was no need for any adjustments to the raw data at all!"?  

 

Hey Mike, no problem.  I went outside of Chester County to find "neighborhood" stations within 30 miles of Coatesville1SW with enough consistent overlapping observations from 1941-1975. We found 6 potential additional “neighborhood” stations but only 2 had enough consistent data Holtwood and Ephrata over the years in question to add to the 3 main Chester County stations above. So what did the analysis find? All 5 raw stations (Coateville 1SW / West Chester 2NW/ Phoenixivlle 1E / Holtwood and Ephrata move together at the same statistically same cooling rate for the same years from 1941-1975 so there is no inconsistent cooling or warming trend for the control station in this analysis (Coatesville 1SW) based on the raw data across these stations. However, as we have found before - the overall NCEI Adjusted Chester County data while following the raw average temperature pattern consistently applied a solid ~1-3 F post hoc adjustment to Coatesville 1SW and all of the 5 stations were chilled by NCEI lower than any of the 5 in the NCEI Chester County wide adjusted annual average temperatures. So for essentially the entire period! This was a clear offset, not a trend divergence. So again what station if not a neighboring station within 30 miles of Chester County was NCEI using to apply non-stop chilling adjustments to Coatsville 1SW to adjust the raw temperatures to even lower levels than they were all showing for all those years? So we know Coatesville 1SW was not adjusted cooler due to Time of Observation bias that was ruled out by majority 8am readings (if anything one could argue for a slight warming adjustment for homogenization) No station moves resulted in significant temperatures changes that were not statistically the same as the other area station trends so we still have no support for the individual Coatesville1SW chilling NCEI adjustments and no support for the overall Chester County historical 1941-1975 chilling adjustments made by NCEI. 

[Mike Cycle]

Paul, using other stations as references will only work if those stations are reference grade themselves.  If there are station moves or other major changes, they are no longer "references".  The stations you have chosen as "references" show 14 detected breaks in the 1941 to 1975 windows alone.  I was working on this graph anyway, see below.

The fact that known good references are so scarce is a major motivation for developing homogenization processes or alternatives like BEST's scalpel.  These methods presume the raw data is replete with breaks and work to overcome this challenge.  Your approach does not.

The September 1921 TOB for Coatesville shows up clearly on the kinds of comparisons seen above. 

 

 

[chubbs]

17 hours ago, Mike Cycle said:

Paul, using other stations as references will only work if those stations are reference grade themselves.  If there are station moves or other major changes, they are no longer "references".  The stations you have chosen as "references" show 14 detected breaks in the 1941 to 1975 windows alone.  I was working on this graph anyway, see below.

The fact that known good references are so scarce is a major motivation for developing homogenization processes or alternatives like BEST's scalpel.  These methods presume the raw data is replete with breaks and work to overcome this challenge.  Your approach does not.

The September 1921 TOB for Coatesville shows up clearly on the kinds of comparisons seen above. 

 

 

Yes stations contaminated with station changes are not suitable references. Myriad station changes are readily apparent on Paul's chart. Just look for a single station with-year-to-year movement different than the others. Between 1941 and 1975, West Chester, Phoenixville, Holtwood and Ephrata all had large station changes making them bad references for Coatesville over that period.

However, there's an easy way to turn these stations from bad into good references. Use shorter time periods without station changes. The station changes only effect a small portion of any one station's 35-year record. The other years are untainted.

Several examples are posted upthread. Here's another : West Chester's 1970 move using monthly data from Phoenixville and Coatesville as the reference. Both stations were stable in this 3-year period. The West Chester station closed at the end of 1969 and re-opened at a new site in May 1970. West Chester cooled immediately on reopening. The stats show a statistically significant 1.4-1.7F cooling relative to Coatesville and Phoenixville due to the move.

This simple analysis only uses 2 reference stations. Many more are available outside of Chester County to further improve the power of the statistics. It is clear that the most important NCEI bias adjustments are highly statistically significant.

[Mike Cycle]

If I understand what you are showing, the two pairs find a shift of -1.67 and -1.44 respectively for West Chester 2NW's April 1970's move.   Averaging 12 station to station pairs before the move, and 16 after.  

It would be straightforward to identify the non-move segments of local stations, and use those to test the others iteratively, building up a timeline for all stations.   Assuming all of the station moves are at HOMR or on the 530-1s, that would still leave the TOB changes.  Coatesville 1 SW switched from 8 PM to 8 AM & 8 PM at the end of October 1921, effectively eliminating the double counting of daily highs, shifting the time series down by  1.4 deg F. 

[chubbs]

22 hours ago, Mike Cycle said:

If I understand what you are showing, the two pairs find a shift of -1.67 and -1.44 respectively for West Chester 2NW's April 1970's move.   Averaging 12 station to station pairs before the move, and 16 after.  

It would be straightforward to identify the non-move segments of local stations, and use those to test the others iteratively, building up a timeline for all stations.   Assuming all of the station moves are at HOMR or on the 530-1s, that would still leave the TOB changes.  Coatesville 1 SW switched from 8 PM to 8 AM & 8 PM at the end of October 1921, effectively eliminating the double counting of daily highs, shifting the time series down by  1.4 deg F. 

You understand what I did correctly. Yes it would be easy to use the stable portions of the Chesco station data to test the others. That's essentially what NCEI does (and other groups). The NCEI adjustments are based on raw temperature data not station information. NCEI also uses data from outside of Chester County to determine Chesco bias adjustments, taking advantage of the fact that weather data is correlated over hundreds of miles.  That's one of the reasons I found your Coatesville analysis interesting. The NCEI adjustments match the detailed site information you developed very well; and. for the periods where your site information was more complete and accurate than NCDCs, the match between the site info and the bias adjustments improved.

Interesting that the West Chester site has data from before 1894. Can you obtain the data? 

[Mike Cycle]

Interestingly, there is pre-1894 data available. From 1873 forward there is daily temperature.  I am somewhat awed by the level of scientific competency shown in these (and other) old records.  

Observer is hard to read, but not Jesse Green.  Almost certainly there are usable archives at West Chester that would provide more information, including photos.  Tracking this stuff down and building a story line would be a perfect cross-disciplinary project for a college intern.

Would you mind if I had Claude run your method above on Chester County and nearby stations?  The output would be a complete human-readable timeline for how reference stations are used to arrive at adjusted records for these stations--something the OP has requested numerous times.  As I understand it the actual NCEI process involves matrix math, too complex for easy communication if you ask me; a manual method using your approach will be easy for anyone to understand.  

 

[chubbs]

3 hours ago, Mike Cycle said:

Interestingly, there is pre-1894 data available. From 1873 forward there is daily temperature.  I am somewhat awed by the level of scientific competency shown in these (and other) old records.  

Observer is hard to read, but not Jesse Green.  Almost certainly there are usable archives at West Chester that would provide more information, including photos.  Tracking this stuff down and building a story line would be a perfect cross-disciplinary project for a college intern.

Would you mind if I had Claude run your method above on Chester County and nearby stations?  The output would be a complete human-readable timeline for how reference stations are used to arrive at adjusted records for these stations--something the OP has requested numerous times.  As I understand it the actual NCEI process involves matrix math, too complex for easy communication if you ask me; a manual method using your approach will be easy for anyone to understand.  

 

No I don't mind running Claude as you describe. Should be useful as a learning tool. 

Berkeley Earth has a West Chester 1 station with data back to Dec 1845, link for West Chester 1 below. The Berkeley Earth write-up for West Chester 2NW says that West Chester 1 is an alternative name for the station. So West Chester 1  may be the older data for West Chester 2NW. Worth checking anyway.

https://data.berkeleyearth.org/stations/35128

 

 

[Mike Cycle]

Yes, there is earlier data, but its not Tmin and Tmax, its 7 AM, 1 PM, and 9 PM.  csv attached.

 

PA_West_Chester.metadata.csv PA_West_Chester.data.csv

[ChescoWx]

I had a request to update the "heatwave" stats to something potentially more meaningful. Which is 3 or more consecutive days with daily maximum temperatures above the 90th and 95th percentile for all Chester County Stations. The below rank summary makes the absolute-vs-relative divergence concrete. Sorted by absolute rank, the biggest movers are the 2010s (11th → 4th) and 2020s (13th → 6th), both rising 7 places once heat is judged against each station's own norm — meaning recent decades have been locally extreme even though they weren't absolutely record-hot. Going the other way, the 1960s (−4) and 1990s (−5) fall under the relative lens, and the 1940s slip from 1st to 3rd. The 1930s hold firm near the top under both definitions, and the 1950s actually take the #1 spot under P90 

[ChescoWx]

2 hours ago, Mike Cycle said:

Yes, there is earlier data, but its not Tmin and Tmax, its 7 AM, 1 PM, and 9 PM.  csv attached.

 

PA_West_Chester.metadata.csv 2.39 kB · 1 download PA_West_Chester.data.csv 1.01 MB · 0 downloads

Thanks Mike!! It looks like there is t-max and t-min starting pretty consistently for West Chester starting late in 1873. I will try to add this to my data set and run some reports! This is great!! If you can find any other stations from before 1894 let me know!

[ChescoWx]

From the analysis by Claude - Coatesville 1SW trends, °C/decade, 1894–1982 - Key headline the adjustments are questionable....

• 1894–1903, mean adjustment applied: −0.72 °C (−1.30 °F) — early years pushed down
• 1972–1981, mean adjustment applied: +0.79 °C (+1.42 °F) — late years pushed up
• Net swing across the record: +1.51 °C (+2.72 °F)

Cool the beginning, warm the end. That's the whole mechanism, and it's why the adjusted series warms while the raw series cools.

Why I put that column in the table rather than the raw trends. The r² of 0.671 is the striking part: 67% of the variance in Berkeley's correction is explained by a straight line in time. These corrections are supposed to be a sum of independent step functions, each fixing an unrelated site or instrument problem at an unrelated date. There's no mechanical reason fourteen such steps should add up to a straight line. That they do — at five of seven stations, all with p < 10⁻⁴ — is the observation worth putting in front of NCEI.

Every single breakpoint is code 4

Fourteen breakpoints: 1896-12, 1902-02, 1917-08, 1920-09, 1922-08, 1930-10, 1936-05, 1941-06, 1946-04, 1959-11, 1968-05, 1971-04, 1973-07, 1976-02. Not one is code 1 (documented move), 2 (gap), or 3 (time-of-observation change) — all fourteen are empirically inferred from neighbor comparison. Given that your HOMR work documents six actual site relocations at this station between 1888 and 1982, Berkeley detected none of them as documented events. Worth cross-checking your Coatesville 1SW History sheet against those fourteen dates: any that coincide with a real move is a defensible correction; any that don't is a correction inferred purely from the neighbors disagreeing.

Of note only Coatesville 2W had a documented flagged station move across the entire Coatesville lineage - in April 2001. That's the first and only documented move Berkeley has flagged anywhere in the Coatesville lineage, against six relocations in your HOMR research and fourteen all-code-4 breaks at 1SW.

[ChescoWx]

4 hours ago, Mike Cycle said:

Yes, there is earlier data, but its not Tmin and Tmax, its 7 AM, 1 PM, and 9 PM.  csv attached.

 

PA_West_Chester.metadata.csv 2.39 kB · 2 downloads PA_West_Chester.data.csv 1.01 MB · 1 download

Interesting in reviewing the data it is apparently an already altered and processed product and not raw!

What about 1855–1892? That's the honest attraction — 462 months, 35 complete years, entirely predating your Source File. But it fails your own standards on three counts:

• Monthly means only. Your Source schema is daily: High, Low, Avg Temp, Precip, Snow, Sn Cover. There's nothing to put in those columns.
• It's a processed product, not raw. Your standing rule is raw observations only, no estimated or filled values. This has passed through CRU's pipeline and carries an undocumented adjustment.
• The 1.32 °C offset almost certainly extends backward. The bias is present throughout the checkable period and drifts at +0.126 °C/dec. Pre-1893 values are probably ~1.3–1.5 °C too cold relative to your network, and there's nothing to calibrate against.