ChescoWx

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.