ChescoWx

A member asked for an analysis of 100 degree days by decade since the 1890's. This is normalized as days per station per year (total 100°F+ days across all stations in a decade, divided by the number of station-years of data in that decade) rather than a raw sum — otherwise a decade with 22 stations would look "hotter" than a decade with 4 stations just from having more thermometers out there, which would be misleading. The pattern holds up clearly at the county level, same as it did for individual stations: the 1930s stand out sharply at about 1.1 days per station per year — nearly double any other decade — consistent with the well-documented Dust Bowl-era heat. From there the rate declines fairly steadily, bottoming out near zero in the 1970s and again in the 2020s (0.01 and 0.02 days/station/year respectively), with the 2000s-2010s sitting in a modest middle range around 0.11–0.15. Worth flagging directly: the two lowest decades in the entire 130-year record are the 1970s and the current 2020s — and the current decade of the 2020s (partial decade).

AI knew the Chesco COOPs are included in the SE PA climate division but did not feel it material enough to change the statistical fact that the raw data at Chesco was cooling the same as the surrounding stations so again no need for further cooling. Plus with all those AM TOB readings at Coatesville and West Chester why didn't NCEI apply some warming adjustments? Again only non-stop chilling adjustments.

Of course @chubbsWidening the interval to 1941 - 1975 does not change the previous answer. Both series show a real, statistically significant cooling trend on their own — this isn't noise, and it fits the well-documented mid-century cooling that shows up across the eastern US from the 1940s into the 1970s. Are the two trends statistically the same? This is the more interesting question, and the answer depends on the test: Naive comparison (treating the two trends as independent): the difference in slopes (−0.66 vs. −0.46 °F/decade) gives t = −0.92, p ≈ 0.36 — not remotely significant. By this test they're indistinguishable. Paired comparison (the right test here, since both series describe the same regional weather in the same years — they're correlated at r = 0.83, so a paired test on the year-by-year difference is more powerful): the difference series trends at −0.021 °F/yr (−0.21 °F/decade), 95% CI [−0.042, +0.001], p = 0.057. So the more rigorous test lands just on the wrong side of the conventional 0.05 cutoff — the station data cooled somewhat faster than the division average, and that gap is close to, but doesn't quite clear, statistical significance. The honest read: the two trends are not clearly, statistically different so no need to cool the raw data further as they are already a strong match.

All three stations cooled at statistically the same rate as the surrounding stations. Additionally, in looking closer at potential TOB adjustments one may wonder why the West Chester 2NW and Coatesville 1SW records which predominantly relied on morning (AM) observations...so one would think the Raw TOB Distortion of an AM reading captures a naturally lower minimum, meaning the raw data was technically already too cool correct? The NCEI Adjustment you would think logically would be to correct for morning bias at Coatesville and West Chester by warming the historical record. However, NCEI's automated, grid-wide homogenization algorithms actually did the opposite by applying additional sweeping chilling adjustments to both of these stations data from 1895 through 1982.

Plenty of lows in the 50's this morning with the lowest being 50.3 degrees at the Warwick DEOS station. Today will be the 10th below average temperature day over the last 15 days. We should continue to see below average temperatures for what is, on average, our warmest week of the year for the rest of this new work week. A beautiful day today with some ridge locations remaining just below 80 degrees. Rain chances increase toward tomorrow morning with the general forecast being for between 3/4 and an inch of rain for most spots with showers lasting till Wednesday AM. We dry out and stay cool on Thursday with highs only in the mid 70's - almost 10 degrees below normal levels for late July.

Plenty of lows in the 50's this morning with the lowest being 50.3 degrees at the Warwick DEOS station. Today will be the 10th below average temperature day over the last 15 days. We should continue to see below average temperatures for what is, on average, our warmest week of the year for the rest of this new work week. A beautiful day today with some ridge locations remaining just below 80 degrees. Rain chances increase toward tomorrow morning with the general forecast being for between 3/4 and an inch of rain for most spots with showers lasting till Wednesday AM. We dry out and stay cool on Thursday with highs only in the mid 70's - almost 10 degrees below normal levels for late July.

So we did a little fact check on Charlie's claim that the raw data cooled more than surrounding stations.....The facts are that the raw cooling data is well supported by the surrounding regions! Below is the AI review of the raw data for the 3 stations in question. What that regional record shows for 1946–1970 Using Penn State's State Climatologist office data (built from this same NCEI divisional dataset): Metric Official SE PA Division (Chester/Berks/Montgomery/Lancaster region) Your 3-station Chesco composite 1946 annual avg 54.0°F — 1970 annual avg 52.4°F — Trend −0.093°F/yr −0.083°F/yr Total change, 1946–1970 −2.23°F −2.00°F R² 0.365 0.352 p-value 0.0014 0.0018 That's a remarkably close match — both in direction, magnitude, and statistical significance. Individually, Phoenixville 1E (−2.34°F, p=0.0008) and West Chester 2NW (−2.48°F, p=0.0014) track the regional figure almost exactly; Coatesville 1SW is a bit weaker (−1.17°F) and only marginally significant on its own (p=0.055), but still points the same direction. Bottom line: Yes, the cooling is well supported by the surrounding region. This is a case where the "raw" county data and the "official" broader regional data agree closely So @chubbs if the cooling in the raw data is statistically the same as the surrounding data why did NCEI choose to chill the raw data further in each and every year between 1946-1970??

In the below 2022 study, "the authors analyzed thousands of different versions of the dataset downloaded over 10 years. They studied the homogenization adjustments for more than 800 European temperature records. They found that these adjustments changed dramatically every day when NOAA re-ran their computer program. The authors found that only 17% of NOAA’s adjustments were consistent from run to run. Furthermore, by compiling historical records known as station history metadata for each of the stations, they were able to compare the adjustments applied by NOAA’s computer program to the documented changes that were known to have occurred at the weather station. They found that less than 20% of the adjustments NOAA had been applying corresponded to any event noted by the station observers - such as a change in instrumentation or a station move." Homogenization of data is badly flawed and should be disregarded as such"The study itself was not focused on the net effects of these adjustments on long-term climate trends. However, the authors warned that these bizarre inconsistencies in this widely-used climate dataset are scientifically troubling. They also are concerned that most researchers using this important dataset have been unaware of these problems until now.https://www.ceres-science.com/post/major-problems-identified-in-data-adjustments-applied-to-a-widely-used-global-temperature-dataset?fbclid=IwY2xjawTJxvZleHRuA2FlbQIxMABicmlkETFRaGlnYzJQQVNzdndoTkdwc3J0YwZhcHBfaWQQMjIyMDM5MTc4ODIwMDg5MgABHlguzGDpWxHyS0ptciE_1okX3LFV-2pBe4Pu2WQnleZLxvskMdPVhhDxQZq5_aem_g_cHQVsBuo4BwgjgPPTV1g

So I asked AI to review the Chester County PA raw data set since 1893 to find if there is a significant p-value that shows warming in this County. The AI review of the data finds clearly that No — the raw Chester County composite does not show a statistically significant warming trend since 1893. The numbers (1893–2025, 133 years) Linear trend: +0.0043°F/year (≈ +0.43°F per century) 95% confidence interval: −0.0012 to +0.0097°F/year — this interval includes zero, which is the definition of "not significant" R² = 0.018 (the trend line explains less than 2% of year-to-year variation) p = 0.128 — above the conventional 0.05 threshold A robust version of the same test (Theil-Sen, less sensitive to outlier years) gives essentially the same answer: +0.40°F/century, still not significant So statistically, you can't distinguish this composite from a flat line over 133 years. Only if we allow NCEI post hoc alterations and adjustments to the raw data can we glean any signifcant p-value warming across Chester County PA! This is how folks lose trust in data when only with post hoc adjustments can we show any significant warming in our climate since 1893!

Below is the first time I have used AI (Claude) to help analyze the Chester County Data set with data from 1893 to Present. Below is the average number of 90+ days by station and month. Including the years of record and the overall annual average. It did this correctly! see below.

I had AI review the raw unadjusted data of those 3 stations from 1945-1980, The Bottom line: the direction, timing, and general shape of the cooling at Coatesville 1SW, Phoenixville 1E, and West Chester 2NW was found to be consistent with the raw data of surrounding stations during the well-documented mid-century cooling seen across the Northeast and eastern U.S more broadly. The magnitude at your stations is plausible relative to hemispheric averages — which fits, since this region was one of the more prominent expressions of that cooling episode with more local variance than a regional composite.

Below is the first time I have used AI (Claude) to help analyze the Chester County Data set with data from 1893 to Present. Below is the average number of 90+ days by station and month. Including the years of record and the overall annual average. It did this correctly! see below.

We have an extended period of below normal temperatures for late July which looks like it will continue through this entire upcoming week. Our warmest and most humid day will be today, but temperatures will be a few degrees cooler than average. Showers and thunderstorms should develop this afternoon and continue till around midnight. Some areas could see over an inch of needed rainfall. The sun returns both tomorrow and Monday with temperatures in the upper 70's to low 80's. Some valley spots may see lows by Monday morning in the comfortable 50's. Shower chances ramp up again by Tuesday and Wednesday before we clear out toward the end of the work week.

We have an extended period of below normal temperatures for late July which looks like it will continue through this entire upcoming week. Our warmest and most humid day will be today, but temperatures will be a few degrees cooler than average. Showers and thunderstorms should develop this afternoon and continue till around midnight. Some areas could see over an inch of needed rainfall. The sun returns both tomorrow and Monday with temperatures in the upper 70's to low 80's. Some valley spots may see lows by Monday morning in the comfortable 50's. Shower chances ramp up again by Tuesday and Wednesday before we clear out toward the end of the work week.

Smoke will continue to be a problem through tonight. We should be several degrees cooler than yesterday with what looks like to me no temps near 90 degrees for at least the next couple of weeks. Tomorrow will be warm and humid with showers and thunderstorms across the area. We turn much cooler by Sunday with highs in the upper 70's to near 80. Nighttime lows by Monday morning will be in the 50's across many of our lower valley locations. Temperatures through the next week look to remain below normal through what is on average our hottest week of the year.

Smoke will continue to be a problem through tonight. We should be several degrees cooler than yesterday with what looks like to me no temps near 90 degrees for at least the next couple of weeks. Tomorrow will be warm and humid with showers and thunderstorms across the area. We turn much cooler by Sunday with highs in the upper 70's to near 80. Nighttime lows by Monday morning will be in the 50's across many of our lower valley locations. Temperatures through the next week look to remain below normal through what is on average our hottest week of the year.

Yesterday was the 5th day this month and season that I recorded a 90+ temperature here in East Nantmeal. This is the 6th most 90+ days I have recorded in a summer season over the last 23 summers. The most being 10 in 2011 with the summers of 2004/2014/2015/2022/2023 seeing no days touching 90 degrees at all. Many spots maybe not the higher ridge locations like EN should reach 90 again although the well-advertised smoke from the Ontario fires could potentially limit daytime heating a bit. We cool back to near normal on Friday and below normal over the weekend and through Monday. Some small rain chances are around this evening but much better chances of widespread rain on Saturday into Saturday Night. We could see widespread totals of much needed rain of at least an inch.

Yesterday was the 5th day this month and season that I recorded a 90+ temperature here in East Nantmeal. This is the 6th most 90+ days I have recorded in a summer season over the last 23 summers. The most being 10 in 2011 with the summers of 2004/2014/2015/2022/2023 seeing no days touching 90 degrees at all. Many spots maybe not the higher ridge locations like EN should reach 90 again although the well-advertised smoke from the Ontario fires could potentially limit daytime heating a bit. We cool back to near normal on Friday and below normal over the weekend and through Monday. Some small rain chances are around this evening but much better chances of widespread rain on Saturday into Saturday Night. We could see widespread totals of much needed rain of at least an inch.

Happy All Star Game Day to those who celebrate! After seeing 6 of the last 8 days with below normal temperatures will return well above normal starting today and lasting through Friday. Most valley spots should reach the 90's today while ridge locations fall a bit short. Tomorrow will be the hottest day with widespread 90's and increasing humidity. We should also see some increasing smoke from a fire in Ontario. Temperatures begin to cool and rain chances increase as we reach the weekend.

Happy All Star Game Day to those who celebrate! After seeing 6 of the last 8 days with below normal temperatures will return well above normal starting today and lasting through Friday. Most valley spots should reach the 90's today while ridge locations fall a bit short. Tomorrow will be the hottest day with widespread 90's and increasing humidity. We should also see some increasing smoke from a fire in Ontario. Temperatures begin to cool and rain chances increase as we reach the weekend.

So cool (at least to me). Over on a local Facebook Page they posted the below article from 1930 about the original trained NWS Cooperative Observer for Coatesville PA - WT Gordon. Mr. Gordon (1888-1930) at that time he was looking to retire from observing the weather... but keep his legacy of accurate weather and climate reporting for Coatesville PA alive. Some of you may not know this but back in 1998 I actually purchased all of the handwritten NWS COOP pages from the NWS for Coatesville 1SW for every month from 1894 through 1948 (I know I am a weather nerd!) At the time this data was not available on the internet so during my many plane trips for work and in my spare time I transcribed by hand each and every day for all of those years into an excel spreadsheet the handwritten daily observations for those 54 years. When that was completed I accessed the data from 1948 through 1998 that was available on line to complete the data set for the NWS COOP stations of Coatesville 1SW (1893-1982) and Coatesville 2W (1983-2007).

So cool (at least to me). Over on a local Facebook Page they posted the below article from 1930 about the original trained NWS Cooperative Observer for Coatesville PA - WT Gordon. Mr. Gordon (1888-1930) at that time he was looking to retire from observing the weather... but keep his legacy of accurate weather and climate reporting for Coatesville PA alive. Some of you may not know this but back in 1998 I actually purchased all of the handwritten NWS COOP pages from the NWS for Coatesville 1SW for every month from 1894 through 1948 (I know I am a weather nerd!) At the time this data was not available on the internet so during my many plane trips for work and in my spare time I transcribed by hand each and every day for all of those years into an excel spreadsheet the handwritten daily observations for those 54 years. When that was completed I accessed the data from 1948 through 1998 that was available on line to complete the data set for the NWS COOP stations of Coatesville 1SW (1893-1982) and Coatesville 2W (1983-2007).

Several of our valley locations this morning saw lows down into the 50's with the ridges remaining in lower 60's. The lowest I could find was 56.3 at the Warwick DEOS. Today will be our 6th below normal temperature day over the last 8 days. We turn that around tomorrow with highs well into the 80's with 90's in the valley spots. Widespread 90's on Wednesday before we back off several degrees by Thursday. So not many spots across Chesco will get to "enjoy" the so called "heat wave" this week. By next weekend we return to near normal temperatures with increasing chances of some showers.

Several of our valley locations this morning saw lows down into the 50's with the ridges remaining in lower 60's. The lowest I could find was 56.3 at the Warwick DEOS. Today will be our 6th below normal temperature day over the last 8 days. We turn that around tomorrow with highs well into the 80's with 90's in the valley spots. Widespread 90's on Wednesday before we back off several degrees by Thursday. So not many spots across Chesco will get to "enjoy" the so called "heat wave" this week. By next weekend we return to near normal temperatures with increasing chances of some showers.

Charlie you keep avoiding my question for the years I am highlighting in the chart 1927-1951. There are 16 years before 1942. To make my question clearer I updated the chart (see below) to add the delta between Allentown and Chesco. You again never answer the question so I will ask it again later. By the way in looking at the surrounding nearby stations at the Navy Yard and Point Breeze it looks clearly like opening of the more rural location with less runways and building etc. at the new PHL Airport resulted in the new site being 1.6 degrees colder than the neighboring Navy Yard in 1941 and continued to run at least 1 degree colder than Point Breeze every year through 1951. So you have to wonder why NCEI failed to warm the new PHL airport site during those years due to the station move to a more rural/colder location? But even without the likely need to warm PHL for those years - the facts remain the same PHL was and is always warmer than average Chesco in every single year except one (1943) ! So I will try again - a simple question why is all of Chester County altered and adjusted to an average temperature for 17 years during this period to colder than Allentown PA?? This is 2 counties north and 50 miles away? Not just Coatesville Charlie - the average of all of these stations. Sorry Charlie in no world should the average temperature for those 25 years have Allentown at 51.8 and the all Chesco Avg. colder at 51.7 Why is NCEI correct based on their adjustments that Chester County should be altered and adjusted to be colder than Allentown for a quarter of a century based on these chilling alterations to the data? Can you answer that?