State by State Climate Series - Actual raw data vs. NCEI 1895 through 2025

[ChescoWx]

Thanks to all of you for the many suggestions to broaden the studies performed by the team at ChescoWx beyond a single county as we have done for Chester County PA! Based on this feedback we are starting a state by state series to illustrate how the actual historical climate records with a focus on how much the annual average temperatures have been systematically adjusted by NCEI with the launch of the USHCN project back the later 1980's and 1990's. To be transparent at least for Chester County PA which was the original focus of the study the gap between the raw county record and NCEI’s Chester County series, we could only find support for about 1/3 of the Chester County adjustments based on documents we found, roughly another quarter could be the observation-time correction (not settled), and about 40% has no independent check. The actual Chester County climate data showed a slight but clearly not statistical warming trend from 1895 through 2025. While the revised NCEI data showed a clear statistically significant warming trend.

If any of you are able to provide detailed support for any of the statistical and methodological data estimates which are what the homogenized NCEI adjustments represent... please provide this detail for these estimates by state if you can - thanks! 

We are undertaking this study following a just completed detailed review of 48 randomly selected based on similar size counties to Chester County PA. We selected 1 County in each of the 48 continguous US States. The findings in those 48 US Counties were consistent with what we saw here in Chester County PA. We found a clear consistent pattern across all 48 stations across the United States of clear cooling of the past records and general warming adjustments to more recent decades. Below are the consolidated findings and the detail of each of those selected 48 US Counties across the entire United States. Based on that finding (see below) of the share of counties where NCEI's adjusted value is cooler than the raw readings by decade....we will start a state by state review to see how many states show significant warming or not based on both the actual and adjusted NCEI data. First up will be my home state of Pennsylvania! I hope you all enjoy this upcoming study series!!