ChescoWx

In my continuing review of after the fact NCEI temperature adjustments for Chester County PA I have reviewed the detailed monthly NCEI average temperatures for all 1,548 months since January 1895. For the first 1,271 months from January 1895 through November 2000. NCEI applied a post hoc chilling adjustment to the reported average temperatures for every single month for each and every year. So for all of those months the average reported temperatures as reported by the NWS Cooperative stations were chilled to an adjusted lower temperature. Since NCEI stopped these non-stop chilling adjustments starting in December 2000... they have now reversed gears and are now applying warming adjustments in 208 of the last 277 months or 75.1% of all months between December 2000 and December 2023. Also of note is that in every single summer month between June and September since way back in June 2006 and continuing through last September 2023....for each of those last 72 consecutive summertime months they have warmed each and every month. Cooling the past and warming the more recent and current years....that will get us to the answer.

In my continuing review of after the fact NCEI temperature adjustments for Chester County PA I have reviewed the detailed monthly NCEI average temperatures for all 1,548 months since January 1895. For the first 1,271 months from January 1895 through November 2000. NCEI applied a post hoc chilling adjustment to the reported average temperatures for every single month for each and every year. So for all of those months the average reported temperatures as reported by the NWS Cooperative stations were chilled to an adjusted lower temperature. Since NCEI stopped these non-stop chilling adjustments starting in December 2000... they have now reversed gears and are now applying warming adjustments in 208 of the last 277 months or 75.1% of all months between December 2000 and December 2023. Also of note is that in every single summer month between June and September since way back in June 2006 and continuing through last September 2023....for each of those last 72 consecutive summertime months they have warmed each and every month. Cooling the past and warming the more recent and current years....that will get us to the answer.

0.58" of rain since yesterday here in East Nantmeal with 0.21" since midnight. Cloudy and chilly weather for May continues through the upcoming weekend with the greatest chances of rain being today and again on Saturday. The sun may should return again by Monday and we should finally see temps rising back to near normal levels again by Tuesday. Chester County records for today: High 95 degrees at Coatesville 1SW (1900) / Low 32 degrees at Devault 1W (1954) / Rain 2.09" at East Nantmeal (2012)

0.58" of rain since yesterday here in East Nantmeal with 0.21" since midnight. Cloudy and chilly weather for May continues through the upcoming weekend with the greatest chances of rain being today and again on Saturday. The sun may should return again by Monday and we should finally see temps rising back to near normal levels again by Tuesday. Chester County records for today: High 95 degrees at Coatesville 1SW (1900) / Low 32 degrees at Devault 1W (1954) / Rain 2.09" at East Nantmeal (2012)

Our wet year (we are almost 6 inches above normal so far in 2024) looks to continue with more shower chances just about every day over the next week with the exception of Friday. With the exception of the wettest day tomorrow we still could see some sun most of those days so not a total wash out! Chester County records for today: High 93 degrees in Phoenixville (1947) / Low 28.1 at Nottingham (2013) / Rain 2.15" at Devault 1W (1978)

Our wet year (we are almost 6 inches above normal so far in 2024) looks to continue with more shower chances just about every day over the next week with the exception of Friday. With the exception of the wettest day tomorrow we still could see some sun most of those days so not a total wash out! Chester County records for today: High 93 degrees in Phoenixville (1947) / Low 28.1 at Nottingham (2013) / Rain 2.15" at Devault 1W (1978)

A great day today with temps well into the 60's to near 70 for most spots. Rain chances ramp up again by later tomorrow and through much of the day on Wednesday. Thursday looks nice but then more shower chances to end the work week and into the weekend. Near normal temps for much of the week. Chester County records for today: High 92 degrees in West Chester (1991) / Low 28 degrees at Coatesville 1SW (1928) / Rain 2.50" Morgantown/Elverson (2002)

A great day today with temps well into the 60's to near 70 for most spots. Rain chances ramp up again by later tomorrow and through much of the day on Wednesday. Thursday looks nice but then more shower chances to end the work week and into the weekend. Near normal temps for much of the week. Chester County records for today: High 92 degrees in West Chester (1991) / Low 28 degrees at Coatesville 1SW (1928) / Rain 2.50" Morgantown/Elverson (2002)

Below is an analysis of 90 degree days at 8 airports across Eastern and for my Central forum friends also East Central PA. The yellow highlights decades that the number of 90 degree days declined at that location. We can clearly see that all locations have shown cyclical variations with the 2000's seeing 5 of 6 stations not starting obs in the 2000's with declining 90 degree days vs the 1990's. The 2010's saw increases at all locations....the 2020's are incomplete but the trend so far this decade has been a split with more 90 degree days at 5 airports and less at 3.

Below is an analysis of 90 degree days at 8 airports across Eastern and East Central PA. The yellow highlights decades that the number of 90 degree days declined at that location. We can clearly see that all locations have shown cyclical variations with the 2000's seeing 5 of 6 stations not starting obs in the 2000's with declining 90 degree days vs the 1990's. The 2010's saw increases at all locations....the 2020's are incomplete but the trend so far this decade has been a split with more 90 degree days at 5 airports and less at 3.

Below is an analysis of 90 degree days at 8 airports across Eastern and East Central PA. The yellow highlights decades that the number of 90 degree days declined at that location. We can clearly see that all locations have shown cyclical variations with the 2000's seeing 5 of 6 stations not starting obs in the 2000's with declining 90 degree days vs the 1990's. The 2010's saw increases at all locations....the 2020's are incomplete but the trend so far this decade has been a split with more 90 degree days at 5 airports and less at 3.

0.16" of rain since midnight here in East Nantmeal. Today will be our 3rd straight below normal temp day with most spots staying in the upper 50's for high temps. The sun returns tomorrow and temps should get close to normal at around 70 degrees. Rain chances again increase for Tuesday and Wednesday before better weather for Thursday and Friday. Chester County wide records for today: High 94 degrees at Phoenixville (1948) / Low 31 degrees at Coatesville 1SW (1907) / Rain 3.07" in West Chester (1943)

0.16" of rain since midnight here in East Nantmeal. Today will be our 3rd straight below normal temp day with most spots staying in the upper 50's for high temps. The sun returns tomorrow and temps should get close to normal at around 70 degrees. Rain chances again increase for Tuesday and Wednesday before better weather for Thursday and Friday. Chester County wide records for today: High 94 degrees at Phoenixville (1948) / Low 31 degrees at Coatesville 1SW (1907) / Rain 3.07" in West Chester (1943)

While today will be a bit warmer and sunnier than yesterday we will still end up with high temps in the low 60's a good 10 degrees cooler than we should be on May 11th. Rain returns tonight into tomorrow before the sun returns Monday. Chester County records for today: High 93 degrees at Kennett Square (1896) / Low 28 degrees at Coatesville 1SW (1947) / Rain 2.95" Phoenixville (1931)

While today will be a bit warmer and sunnier than yesterday we will still end up with high temps in the low 60's a good 10 degrees cooler than we should be on May 11th. Rain returns tonight into tomorrow before the sun returns Monday. Chester County records for today: High 93 degrees at Kennett Square (1896) / Low 28 degrees at Coatesville 1SW (1947) / Rain 2.95" Phoenixville (1931)

0.30" of rain here in East Nantmeal since yesterday with 0.17" since midnight. Today will be unseasonable chilly and wet day with temps in some higher spots remaining in the 40's. A brief break tomorrow with some sun before rain returns late at night into Sunday. One more nice day on Monday before showers return for much of the remainder of the week. Chester County daily records for today: High 94 degrees at Coatesville 1SW (1896) / Record low 27 degrees at Coatesville 1SW and Devault 1W (1966) / Rain 1.76" at Coatesville 2W (1990)

0.30" of rain here in East Nantmeal since yesterday with 0.17" since midnight. Today will be unseasonable chilly and wet day with temps in some higher spots remaining in the 40's. A brief break tomorrow with some sun before rain returns late at night into Sunday. One more nice day on Monday before showers return for much of the remainder of the week. Chester County daily records for today: High 94 degrees at Coatesville 1SW (1896) / Record low 27 degrees at Coatesville 1SW and Devault 1W (1966) / Rain 1.76" at Coatesville 2W (1990)

I guess if you think an average of 16.6 days in the 1950's dropping to 13.7 in the 2000's is an uptrend not much we can talk about. The 2010's only have complete Glenmoore data....

UHI post obs adjustments by year

So while we often talk about the chilling adjustments done to older data for their biases. Where is the cooling UHI adjustments for PHL???? I am told NCEI accounts for known UHI bias. Do we think there is no UHI impact at PHL?? Tell me what I am missing as I know you will! LOL!!! Below is an analysis of the PHL Airport average annual temperature from 1941 through 2023. I have overlaid the adjusted NCEI temperatures vs the actual reported averages. Why in the last 30 years have the PHL Airport Temps been adjusted upward in 19 of the last 30 years despite UHI?? And the overall cumulative adjustments over those years has been an overall net upward adjustment of 3.45 degrees in PHL actual reported temps. Thoughts????

The city was also way less built up and the UHI factor was not nearly so impactful as today. Regarding near the old normal of 14 days before UHI PHL has been close or below that figure in 2014 (19) / 2009 (15) / 2004 (9) / 2000 (10) / 1996 (7) and 1992 (14)

Climate changer couple things. See above the Coatesville 2W trend is not positive over the period. Just to clarify I have used the same equipment for 21 years in East Nantmeal so no changes or variations there!! Does that help?

Because we actually do have the data let's review Charlie's statement that "the older stations with longer records: GlenmooreCoop, Honey Brook and Coatesville,all have a similar and increasing level of 90F days over multiple decades" Well the actual data Charlie references is below (the yellow highlights are incomplete decades) However, in reality all of the mentioned stations they are the opposite of trending toward an increasing level of 90 degree days. In fact they have trended downward in 90+ days in the complete decades since the 1980's!! Again so different from the UHI problems at PHL. But overall absolutely no clear trend -simply cyclical changes by decade as we have always seen.

This is not difficult Charlie the bias in the overall Chesco data is as of the last couple years now actually biased to the warmer lower elevation locales not the higher! In 2023 there are 11 lower elevation spots vs 6 higher. This is why we now have split the data to account for such biases.

An increasingly chilly day with the wind becoming onshore from the chilly atlantic waters today. Shower chances increase this afternoon. Tomorrow will be a very raw day for May with temps in the higher spots of Chester and Berks counties struggling to escape the 40's to around 50 degrees. Saturday looks like the driest day of the weekend. But the weekend as a whole will not be a washout. Chester County wide records for today: High 96 degrees at Phoenixville (1936) / Low 25 degrees at Coatesville 1SW (1947) / Rain 2.46" at Glenmoore (1992)