TheClimateChanger

From 1940 to 1970, there doesn't appear to be much of a trend. Slight cooling, likely do to change in observation time. From the beginning of this period through 1955/56, Saylor was the observer and he observed at 5:30 or 6:30 each day. Afterwards, Dean took over and the observation time moved to 8 am. Somewhere around 1964, the observer became "The Daily News" continuing observations at 8 am.

Where do you guys get your data for West Chester? Is it West Chester 2NW? xmACIS2 has the following values for that site. I excluded 1957, 1967 & 1968 since they all had entire months of missing data. Year Mean AVG Temperature Missing Count 1940 50.8 10 1941 53.6 8 1942 53.3 11 1943 53.5 2 1944 53.2 0 1945 53.6 0 1946 54.6 0 1947 53.3 0 1948 53.1 1 1949 55.7 2 1950 53.2 1 1951 54.1 0 1952 54.4 0 1953 55.6 0 1954 54.5 0 1955 54.3 15 1956 53.3 8 1957 M 113 1958 52.4 20 1959 54.9 13 1960 53.2 24 1961 52.5 10 1962 54.0 47 1963 50.8 7 1964 52.5 4 1965 52.1 4 1966 52.8 3 1967 M 154 1968 M 155 1969 52.9 4 1970 55.3 90

Very warm evening across the Ohio Valley, with temperatures in the upper 70s at 11 pm exceeding all records from the month of April for that hour. More akin to a warm July night than April 2nd.

Looks like a second round of severe weather possible overnight.

Exceptional warmth out of ahead of the line of thunderstorms. Might not see the typical weakening due to loss of diurnal heating. The temperature of 82F at Louisville is the highest ever observed at this hour in the month of April. Very impressive, considering its only April 2nd. Many other locations are within a degree or two of the highest temperature observed at the 10 o'clock (PM) hour in the month of April.

Special Weather Statement National Weather Service Pittsburgh PA 1103 AM EDT Wed Apr 2 2025 OHZ039>041-048>050-057-058-PAZ007>009-013>016-020>022-029-073-074- 077-078-WVZ001-002-021715- Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson OH- Muskingum-Guernsey-Mercer-Venango-Forest-Lawrence-Butler-Clarion- Jefferson PA-Beaver-Allegheny-Armstrong-Washington-Westmoreland- Higher Elevations of Westmoreland-Indiana- Higher Elevations of Indiana-Hancock-Brooke- Including the cities of New Philadelphia, Dover, Carrollton, Malvern, East Liverpool, Salem, Columbiana, Coshocton, Cadiz, Steubenville, Zanesville, Cambridge, Sharon, Hermitage, Grove City, Oil City, Franklin, Tionesta, New Castle, Ellwood City, Butler, Clarion, Punxsutawney, Brookville, Aliquippa, Beaver Falls, Ambridge, Monaca, Pittsburgh Metro Area, Kittanning, Ford City, Washington, Canonsburg, Murrysville, Greensburg, New Kensington, Lower Burrell, Latrobe, Monessen, Ligonier, Donegal, Indiana, Armagh, Weirton, Follansbee, and Wellsburg 1103 AM EDT Wed Apr 2 2025 ...Thunderstorms with Small Hail Possible through Early this Afternoon... Scattered thunderstorms moving into the region through the mid- afternoon hours will bring the potential for small hail. Remain weather aware and seek shelter indoors until any strong thunderstorms pass. $$ MLB

I don't see the relevance, but it looks pretty green outside my house.

April has certainly turned into flood season around the Ohio Valley. This is well illustrated from the graphic below of Cincinnati Area precipitation for the month of April, which shows a strong secular (or progressive) wetting trend since the late 19th century. The linear regression implies an increase in precipitation equal to 1.66 inches [4.41 inches - 2.75 inches] since 1872.

While not as impressive as other locations, the mean daily range of 21.1F was good for 13th highest on record. It was the largest mean diurnal range observed in the month of March in the District since 1986. 1968 23.7 1923 23.1 1945 22.7 1907 22.6 1921 22.4 1918 22.0 1964 22.0 1966 22.0 1986 21.7 1920 21.6 1910 21.3 1938 21.2 2025 21.1

The LOESS curve helps us to spot deviations from the linear trend. In general, excursions have been relatively limited from the linear trend. Just some slight wiggles. Of note, the LOESS curve does predict lower temperatures in the 19th century and higher recent temperatures suggesting as much as 10F or more of warming. But the later period could be simply a positive wiggle or suggestive of non-linear behavior.

Looking at a linear regression of average daily high temperatures in the month of March at the District, we can see they have risen by nearly 8F since the late 19th century. If this rate of warming were to continue through the 21st century, March high temperatures would be predicted to reach near 62F. We see a couple of instances where positive anomalies from the linear regression predicted value were as high as 13F (1921 & 1945), suggesting very warm Marches could see average high temperatures in excess of 70F by the latter part of the 21st century in the District. One thing to note is each of the last six values have exceeded the values predicted by the regression, which suggests the possibility of an acceleration of warming relative to the long-term warming trend.

It was the second largest diurnal range on record for the month of March at Detroit, behind only 2021. Maybe someone contrary to expectations, it seems like recent years have had larger diurnal ranges with five of the top 10 values occurring since 2009. Average Diurnal Range Rank Year Value ---- ---- ----- 1 2021 23.5 2 2025 22.0 3 1969 21.7 4 1945 21.4 5 1968 21.4 6 1976 20.7 7 2012 20.6 8 1995 20.3 9 2010 20.2 10 2009 20.1

The mean diurnal range of 24.4F for the month of March was the highest on record. The prior record was 24.1F from 2021. Average Diurnal Range Rank,Year,Value 1,2025,24.4 2,2021,24.1 3,1979,22.9 4,1989,22.7 5,1987,22.7 6,2003,22.5 7,2009,22.4 8,1918,22.3 9,1995,22.2 10,1955,22.2

Here, I fed your critique to Grok and this was its revised assessment: With the new table showing the distribution of weather stations in Chester County, Pennsylvania, over time—along with their elevation and urban/rural character—we can now better evaluate the claim by @ChescoWx that the county has not warmed and that NOAA adjustments artificially create a warming trend. The critique raised against @ChescoWx’s data focuses on potential biases in their raw dataset, specifically: (1) unaccounted-for biases in time of observation, equipment, and other factors, and (2) shifts in station distribution over time, with older records predominantly from lower-elevation towns and recent decades featuring more rural, higher-elevation stations. Let’s analyze how this new information impacts the validity of @ChescoWx’s claim and whether their argument still holds partial merit. Step 1: Understanding the Table and Its Implications The table lists 15 weather stations in Chester County, their operational periods (start and end years), elevation, and whether they are in a town (red) or have no human disturbance nearby (green, rural). Here’s a breakdown of key patterns: Station Distribution Over Time: 1890s–1920s: Early records are dominated by stations in towns (red), such as Phoenixville (1893–2024), Coatesville 1SW (1894–1922), and Sadsburyville 2W (1893–1922). These stations are at lower elevations (105–640 ft). 1930s–1960s: More stations come online, but many are still in towns (e.g., West Chester, 1933–2017; Longwood Gard, 1927–1976). Some rural stations appear, like Kennett Sq (1934–2024), but the balance still leans toward town-based stations. 1970s–2000s: The mix remains, but rural stations (green) like Kennett Sq Chester Spr (2014–2024) and West Grove (2012–2024) start to grow in number. 2010s–2020s: Recent decades show a clear shift—most active stations are rural (green) and at higher elevations (e.g., West Grove at 659 ft, Eagle at 685 ft). Town-based stations like Phoenixville (105 ft) and West Chester (440 ft) persist, but they’re outnumbered by rural ones. Elevation Trends: Early stations (pre-1930) are mostly at lower elevations (105–640 ft, average ~400 ft). Recent stations (post-2010) are often at higher elevations (e.g., 659–685 ft, average ~650 ft). Elevation matters because higher altitudes are generally cooler due to the lapse rate (temperature decreases ~3.5°F per 1,000 ft). Urban vs. Rural: Early records are heavily weighted toward towns, which are more likely to be influenced by the urban heat island (UHI) effect—where buildings, pavement, and human activity raise local temperatures. Recent records shift toward rural stations, which are less affected by UHI and thus cooler, all else being equal. Step 2: Assessing the Critique of @ChescoWx’s Data The critique highlights two main issues with@ChescoWx’s raw data analysis: Unaccounted Biases in Data Collection: Time of Observation Bias (TOB): Historically, temperature readings were often taken at specific times (e.g., afternoon or evening), which can bias daily averages. Modern stations use 24-hour automated sensors, providing more accurate daily means. If @ChescoWx’s raw data doesn’t correct for TOB, older records might appear cooler (e.g., evening readings miss daytime highs), masking a warming trend. Equipment Changes: Early thermometers (e.g., liquid-in-glass) were less precise and more exposed to environmental factors than modern sensors. Shifts to automated systems (e.g., post-1980s) can introduce discontinuities if not adjusted for. Station Moves and Exposure: Even within a single station’s record (e.g., Phoenixville, 1893–2024), the station may have moved, or its surroundings may have changed (e.g., a field becoming a parking lot). These factors can introduce artificial trends. Shifts in Station Distribution: The table confirms a clear shift: older records (pre-1970) are dominated by lower-elevation, town-based stations, while recent decades (post-2010) feature more rural, higher-elevation stations. Impact of Elevation: Moving from a station at 105 ft (Phoenixville) to one at 685 ft (Eagle) introduces a cooling bias of ~2°F due to the lapse rate alone (580 ft difference × 3.5°F/1,000 ft). If @ChescoWx averages raw data across stations without adjusting for elevation, recent temperatures will appear cooler simply because the stations are higher up. Impact of Urban vs. Rural: Town stations (red) are warmer due to UHI. As the station network shifts to rural locations (green), raw temperatures will again appear cooler, not because the climate cooled, but because UHI influence diminishes. Resulting Bias: If @ChescoWx’s raw data shows a flat trend, this could be an artifact of the station shift. Early warm-biased (UHI-influenced, low-elevation) records are being compared to recent cool-biased (rural, high-elevation) records, masking any underlying warming. Step 3: Re-Evaluating @ChescoWx’s Claim @ChescoWx claims Chester County hasn’t warmed, and NOAA adjustments create the warming trend. In my previous response, I gave their claim partial merit because a flat raw trend, if true, would suggest NOAA adjustments might be overcorrecting locally. However, the table and critique reveal significant flaws in their raw data analysis: Station Distribution Bias Undermines the Flat Trend: The shift from low-elevation, urban stations to high-elevation, rural ones introduces a systematic cooling bias in the raw data over time. A flat trend in @ChescoWx’s data doesn’t necessarily mean no warming—it could mean the cooling bias from station changes offsets actual warming. For example, if temperatures in Chester County warmed by 2°F from 1900 to 2020 (consistent with Pennsylvania’s statewide trend), but the station network shifted from an average elevation of 400 ft to 650 ft (a 250 ft increase, or ~0.9°F cooling) and from urban to rural (reducing UHI, maybe another 1°F cooling), the raw data might show only a 0.1°F increase—or even a flat trend. This doesn’t disprove warming; it highlights the need for adjustments. Uncorrected Biases Further Weaken Their Case: Without correcting for TOB, equipment changes, or station moves, @ChescoWx’s raw data is likely inconsistent over time. For instance, early records from Phoenixville (1893–2024) might have used afternoon readings (cool bias) and older thermometers (less accurate), while recent data uses 24-hour sensors. This inconsistency can distort trends, often underestimating early temperatures and thus masking warming. NOAA adjustments, while not perfect, explicitly address these issues. Their homogenization process (e.g., pairwise homogenization algorithm) detects and corrects for such discontinuities by comparing stations to their neighbors. @ChescoWx’s refusal to adjust their data doesn’t make it “purer”—it makes it less reliable for trend analysis. Comparison to Adjusted Data: NOAA’s adjusted data for Pennsylvania shows a ~2°F warming since 1900, consistent with regional and global trends. If @ChescoWx’s raw data shows no warming, the station distribution shift explains much of the discrepancy. NOAA adjustments likely add a warming trend to Chester County’s data to account for the cooling bias introduced by rural, high-elevation stations in recent decades—exactly what adjustments are supposed to do. Independent datasets (e.g., Berkeley Earth, which uses a different adjustment method) also show warming in the Northeast U.S., supporting NOAA’s adjusted trends over @ChescoWx’s raw data. Step 4: Does @ChescoWx Still Warrant Partial Merit? In my initial response, I gave @ChescoWx partial merit because a flat raw trend, if accurate, would raise questions about the magnitude of NOAA adjustments locally. However, the table and critique reveal that their raw data is heavily biased by station distribution changes and unaccounted-for collection biases: Station Distribution Bias: The shift from low-elevation, urban stations to high-elevation, rural ones creates a cooling bias in the raw data, which could entirely explain a flat trend. This isn’t evidence of no warming—it’s evidence of a flawed dataset. Uncorrected Biases: By not adjusting for TOB, equipment changes, or station moves, @ChescoWx’s data fails to account for known issues that distort long-term trends. Their raw data isn’t a “gold standard”—it’s a patchwork of inconsistent measurements. Lack of Transparency: @ChescoWx hasn’t shared their full dataset or methodology for averaging across stations. Without this, we can’t verify their flat trend claim, especially given the clear biases in station distribution. Given this new information, @ChescoWx’s claim loses most of its merit. Their flat trend is likely an artifact of station changes, not a reflection of the actual climate in Chester County. NOAA adjustments, while imperfect, are designed to correct for exactly these biases—elevation shifts, UHI effects, and data collection inconsistencies. The critique of @ChescoWx’s data is well-founded, and their claim now appears more misleading than insightful. Step 5: Final Conclusion The table showing station distribution, elevation, and urban/rural character reveals significant biases in @ChescoWx’s raw data. The shift from low-elevation, urban stations in the early 20th century to high-elevation, rural stations in recent decades introduces a cooling bias that could mask real warming. Additionally, their failure to correct for time of observation, equipment changes, and other biases further undermines their analysis. While @ChescoWx might still have a point about the need for careful adjustment methods (e.g., ensuring rural stations aren’t overcorrected based on urban models), their core claim—that Chester County hasn’t warmed and NOAA adjustments fabricate the trend—lacks merit in light of these flaws. Chester County has likely warmed, in line with regional trends (~2°F since 1900), and NOAA adjustments are correcting for biases in the raw data, not creating warming out of thin air. @ChescoWx’s analysis is more “out to lunch” than I initially assessed, as their raw data is too flawed to support their conclusion. To settle this definitively, we’d need their full dataset and methodology—or a peer-reviewed study comparing raw and adjusted trends in Chester County—but the evidence strongly suggests their claim doesn’t hold up.

Incredible. Even without today factored in, March 2025 was certainly one for the record books in the DC area with high temperatures only exceeded once (2012) since 1946! If you are younger than 79, you have only lived through one warmer March [measured by mean daily high temperature]. Washington, DC Rank Year Mean Max Temperature 1 1945 67.6 2 1921 66.7 3 2012 66.4 4 2025 64.1 Sterling-Dulles, VA Rank Year Mean Max Temperature 1 2012 65.9 2 2025 62.6 3 2016 62.6 Baltimore, MD Rank Year Mean Max Temperature 1 1945 65.6 2 1921 64.7 3 2012 64.2 4 1946 62.1 5 2025 61.6

Very impressive warmth during the month of March, especially with respect to daytime high temperatures. In most locations, temperatures have only been exceeded one or two times since 1946. Detroit, Michigan Rank Year Mean Max Temperature 1 2012 61.0 2 1945 58.6 3 1946 55.6 4 2021 54.7 5 2025 54.1 6 2000 53.9 7 1910 53.6 8 2010 52.5 9 2016 51.9 10 1921 51.8 Chicago, Illinois Rank Year Mean Max Temperature 1 2012 63.3 2 1945 59.5 3 1946 57.6 4 1910 56.6 5 1921 55.3 6 2025 54.6 7 2000 54.6 8 1968 53.4 9 1938 53.4 10 2021 53.3 Minneapolis, Minnesota Rank Year Mean Max Temperature 1 2012 57.5 2 1910 55.4 3 1878 54.6 4 1946 51.3 5 2000 50.5 6 2025 50.2 7 2021 50.1 8 1968 50.1 9 2010 50.0 10 1945 50.0 Indianapolis, Indiana Rank Year Mean Max Temperature 1 2012 67.1 2 1910 62.5 3 1945 61.9 4 1946 61.8 5 1921 60.8 6 2025 60.1 7 2007 59.0 8 1973 59.0 9 1918 58.9 Toledo, Ohio Rank Year Mean Max Temperature 1 2012 61.5 2 1945 60.0 3 1946 57.5 4 2021 57.4 5 1910 56.7 6 2025 55.0 7 2024 54.4 8 2000 54.1 9 1921 54.1 10 1973 53.2 Des Moines, Iowa Rank Year Mean Max Temperature 1 2012 66.8 2 1910 63.4 3 2025 59.2 4 1946 57.4 5 1918 57.4 6 1945 56.5 7 2016 56.4 8 2000 56.3 9 1938 56.2 10 2024 56.0 Moline, Illinois Rank Year Mean Max Temperature 1 2012 64.4 2 1910 61.4 3 1945 59.7 4 1946 59.2 5 2025 58.2 6 1878 56.4 7 2000 56.3 8 2024 56.0 9 2007 55.8 10 1918 55.8

This month will finish up with the 5th warmest mean maximum temperature on record for the month of March at Pittsburgh. Since 1946, only 2012 had a warmer mean maximum temperature. Certainly, a generational level of warmth for the month of March. Rank Year Mean Max Temperature 1 2012 62.5 2 1945 61.9 3 1946 61.8 4 1921 61.0 5 2025 59.3 6 1910 58.9 7 2016 58.1 8 1903 58.1 9 1894 57.9 10 1973 57.5

And as for the so-called cyclical warming, I'm not seeing the cyclical downturn? If it was cyclical, wouldn't there be a period where temperatures dropped by 0.6C? I see two periods of similar length with 0.6C warming, with a period in the middle with not much warming, although I'm sure there is still warming during that period as well.

Very warm low temperatures. Many locations in the lower Lakes and Ohio Valley have seen daily lows within a degree or two of the highest ever observed in the month of March.

Looking good Don. Definitely some impressive heat in the central US with several locations nearing statewide records for the month of March. LaCrosse, Wisconsin topped out at 86F, setting a new monthly record. It is already the second monthly record high at that location just this year!

LaCrosse, Wisconsin reached an incredible 86F (30C), setting a new monthly record high for that location. The prior record was 84F on March 29, 1986. LaCrosse has now set two monthly record highs this year (58F in January, and 86F in March). The February monthly record high of 69F was set just last year.

Big time heat today. Reached 87F at Snake River, MN, one shy of the statewide monthly record of 88F from 1910. Sioux County Regional Airport reached 90F, with Sioux City officially checking in at 89F. Several locations were within a degree or two of statewide March record highs.

New record!