TheClimateChanger

I wanted to take a closer look at the claim that NOAA/NCEI’s July 2026 temperature ranking is largely the product of “tampering” or adjustments to the historical temperature record. Tony Heller has advanced this claim on X/Twitter, and we've seen similar claims made by members here (cough, cough, ChescoWx). So I downloaded the raw USHCN Tmax and Tmin monthly data directly from NOAA, without applying NOAA’s homogenization adjustments, and tried to see how far one can get using the raw observations alone. The results were pretty illuminating. The first issue is that simply averaging the absolute temperatures of all available USHCN stations each year is not a very good way to construct a national temperature series. Although USHCN contains 1,218 designated stations, nowhere near 1,218 stations report in every July. The number of stations with both Tmax and Tmin data increased from only about 528 in 1895 to roughly 1,200 by the 1930s–1960s, then began declining sharply in recent decades: 1990: 1,180 2000: 1,115 2010: 980 2020: 779 2025: 730 2026: 458 so far in the August 12 archive That creates a compositional problem. If the stations disappearing from the network are climatologically warmer or cooler than those remaining, the simple national average can change even if temperatures at every individual station do not. Note that 2026 data is provisional, as a lot of stations are not yet reported in the dataset file. Step 1: Calculate station anomalies To deal with this, I calculated a 1951–1980 July climatology for each individual USHCN station. This was a particularly useful reference period because station coverage was near its peak; 1,217 of the 1,218 stations had sufficient data to calculate a usable climatology. For every station and every July, I then calculated: July anomaly = observed July temperature − that station’s own 1951–1980 July mean This removes most of the changing-station-composition problem, because a hot station disappearing from the network no longer mechanically lowers the national average merely because its absolute climatological temperature was higher. That made a surprisingly large difference in recent decades. For July Tmax from 1990–2025: simple raw station-average trend: +0.35°F/decade station-anomaly trend: +0.55°F/decade composition effect: about −0.20°F/decade From 2000–2025: simple raw Tmax trend: only +0.09°F/decade station-anomaly trend: +0.34°F/decade composition effect: about −0.25°F/decade Why? Because the climatological July Tmax of the stations actually reporting has declined substantially: Year Mean July climatology of reporting Tmax stations 1990 87.39°F 2000 87.43°F 2010 87.31°F 2020 86.96°F 2025 86.88°F In other words, the modern USHCN reporting network has increasingly become composed of cooler stations. Simply averaging their absolute temperatures therefore introduces an artificial cooling tendency. The same phenomenon appears in Tmin. Using an equal-station anomaly calculation, July 2026 came out approximately: Tmax: +1.66°F Tmin: +3.71°F Tavg: +2.68°F On that basis, 2026 ranked roughly: 14th warmest Tmax 1st warmest Tmin 5th warmest Tavg But there was still another problem. Step 2: Geographic weighting A station in a densely sampled part of Ohio should not carry the same national weight as a station representing a huge area of Nevada, Montana, or Wyoming. So I took the raw USHCN station anomalies and placed them on a fixed 0.25° CONUS land grid. Each grid cell was assigned the anomaly of its nearest reporting USHCN station, and the resulting cells were area-weighted using the cosine of latitude. This is essentially a simple Voronoi-style geographic weighting. Importantly, it does not use NOAA homogenization. It does not alter the raw station observations. It merely prevents regions containing many stations from receiving disproportionately large weight in the national average. The effect was substantial. After rebasing our resulting national series to the same 1901–2000 reference used by NCEI, several important Julys looked like this: Year Equal-weight raw USHCN Area-weighted raw USHCN NCEI 1901 +3.25°F +2.55°F +2.60°F 1934 +2.99°F +2.87°F +2.72°F 1936 +3.32°F +3.29°F +3.14°F 1980 +2.02°F +2.12°F +2.09°F 2000 −0.59°F +0.02°F +0.22°F 2006 +2.32°F +2.59°F +2.76°F 2012 +3.15°F +2.95°F +3.10°F 2022 +2.02°F +2.56°F +2.76°F 2023 +1.25°F +1.76°F +2.02°F 2024 +1.47°F +1.77°F +2.07°F 2026 +2.67°F +3.15°F +3.26°F The 1901 result is especially revealing. Under a naïve equal-station average, 1901 appeared about 0.65°F warmer relative to NCEI. Once the raw observations were geographically weighted, the discrepancy collapsed to about 0.05°F. The same thing happened at the other end of the record. Our equal-station calculation put 2026 at only about +2.67°F, compared with NCEI’s +3.26°F. Geographic weighting alone moved the raw-USHCN result to +3.15°F. No homogenization adjustment was necessary to explain most of that gap. Final raw-USHCN ranking Using the geographically weighted raw station anomalies, the leading Julys were: 1936: +3.29°F 2026: +3.15°F 2012: +2.95°F 1934: +2.87°F 2006: +2.59°F 2022: +2.56°F 1901: +2.55°F NCEI places 2026 slightly ahead of 1936 instead: 2026: +3.26°F 1936: +3.14°F So after controlling for station composition and geographic weighting, the difference between our deliberately simple raw-data-only method and NCEI is not some enormous discrepancy. Our raw calculation has 1936 about 0.15°F warmer than 2026. NCEI has 2026 about 0.12°F warmer than 1936. That leaves only about a 0.27°F swing in their relative difference between our raw-data method and the full NCEI analysis. Now compare the entire records This was perhaps the most surprising result. Once the raw USHCN observations are converted to station anomalies and geographically weighted, the resulting curve lies almost directly on top of the official NCEI series. Across 1895–2026, the mean absolute difference between the two annual July anomaly series is only about 0.11°F. And remember what went into our series: raw USHCN observations individual station climatologies geographic weighting That's it. No NOAA homogenization adjustments were applied. What does this actually tell us? This certainly does not demonstrate that every NOAA adjustment is perfect, nor does our simple experiment precisely reproduce NOAA’s methodology. NOAA uses a larger station network, homogenization, and substantially more sophisticated spatial interpolation. But it does demonstrate something important. Most of the apparent disagreement between a naïve “raw USHCN” calculation and NOAA/NCEI can be reproduced without changing a single thermometer observation. Two mundane methodological problems explain an enormous portion of it: Changing station composition Unequal geographic station density The raw USHCN network has lost hundreds of reporting stations in recent decades, and the stations disappearing have, on average, been climatologically warmer than those remaining. That artificially suppresses recent temperatures if one simply averages absolute station readings. Meanwhile, equal station weighting gives densely sampled portions of the country far too much influence. Correcting that spatial bias pushes recent hot years upward and, in some cases, early hot years downward. The transformation of 1901 is particularly instructive: Naïve raw USHCN: +3.25°F Geographically weighted raw USHCN: +2.55°F NCEI: +2.60°F And for 2026: Naïve raw USHCN: +2.67°F Geographically weighted raw USHCN: +3.15°F NCEI: +3.26°F So when someone produces a graph of “raw USHCN temperatures” and argues that the difference from NOAA must therefore have been manufactured through data adjustments, there is a very large omitted variable: how the raw data are aggregated in the first place. A simple station-anomaly calculation plus basic geographic weighting — using the unaltered raw observations themselves — gets astonishingly close to the official NCEI record.

Yeah, that was the case in Cleveland as well. I think I read 22”, but unfortunately no official snowfall records at that time. The official records only note 1.85” of liquid equivalent. The article below is probably an exaggeration (20” in 3 hours), but I did read elsewhere there were insane rates… however, if memory serves, it was more like 8” in 2 or 3 hours.

@donsutherland1 @bluewave Retracting my earlier analysis, because I think it was caused by the way NOAA attributes data for the cooperative stations. Most report in the morning and the high and low get attributed to the day of reporting, even though it reflects the prior day. So, I think most of the discrepancy in July was due to the co-op stations having an extremely hot June 30th attributed to July 1, which gave them an extra hot day last month.

You have to take some of these high dewpoints from 1995 with a grain of salt. The chilled mirror sensors in use at the time had to be regularly cleaned or they could produce spuriously high readings.

Incredible. New York has set or tied 10 August monthly hourly dewpoint maximum temperatures during this torrid stretch (based on hourly data to 1943).

No, July 2012 came in 0.04F cooler than July 1936, per NCEI. Close but no cigar. For the whole summer (JJA), 2021 is tied with 1936 for the record at 73.98F.

At least one of those so-called monthly record lows is fraudulent - there's a spurious 18F reading at YNG reported on 5/24 for some reason. Also, strongly disagree with Brian about the upcoming pattern trending away from the record. In fact, this is the hottest stretch of the month starting today. NWS NBM forecast shows several days of 3-5F above normal to close out the month.

Wow, wouldn't have thought it had been that long since a July high below 75F. The coolest Julys of the past would see the entire month's average not much higher than 75F (e.g., 1976 - 76.7F).

Is there a way to fix a data error in the official climate records? I noticed from Brian Brettschneider's map, it was showing a monthly record low at Youngstown - which struck me as odd. I took a look and the low for May 24th is showing up as 18F, which is obviously incorrect. Not sure how that ended up there... it doesn't look like NWS CLE generated/published an RER for that date.

A code *maroon* air quality alert for northern Ohio. Geez, I didn’t even know it had that many colors. OHZ010>014-020>022-089-170400- Lorain-Cuyahoga-Lake-Geauga-Ashtabula Inland-Medina-Summit-Portage-Ashtabula Lakeshore- Including the cities of Lorain, Elyria, North Ridgeville, Avon Lake, Cleveland, Mentor, Willoughby, Eastlake, Painesville, Willowick, Wickliffe, Chardon, South Russell, Bainbridge, Chesterland, Middlefield, Burton, Jefferson, Orwell, Andover, Roaming Shores, Brunswick, Medina, Wadsworth, Akron, Kent, Aurora, Streetsboro, Ravenna, Ashtabula, Conneaut, and Geneva 530 PM EDT Wed Jul 15 2026 ...AIR QUALITY ADVISORY IN EFFECT FOR THURSDAY JULY 16... An Air Quality Advisory for ground level fine particles has been issued by the Northeast Ohio Areawide Coordinating Agency for Ashtabula, Cuyahoga, Geauga, Lake, Lorain, Medina, Portage and Summit Counties. The advisory is from midnight tonight to midnight Thursday night. A code MAROON air quality alert means that air pollution concentrations within the local region are extremely hazardous for the general population. Efforts to minimize effects, even indoors, may be difficult to impossible. Follow local emergency instructions via television or radio. To help our region reduce air pollution: * Drive less: bike, walk, use transit, work from home, combine trips * Visit gohiocommute.com/noaca - Find a smarter way to travel! * Don`t idle - Turn off your engine * Refill your tank after sunset * Wait to mow the lawn && The Northeast Ohio Areawide Coordinating Agency (NOACA), in partnership with the Ohio Environmental Protection Agency (Ohio EPA), the Cleveland Division of Air Quality, the Akron Regional Air Quality Management District, the Akron Metropolitan Area Transportation Study, the Lake County General Health District, and Ohio University, has forecasted this Advisory based on predicted weather patterns. Learn more at www.noaca.org. $$

Impressive heat. Highest in the month of July since 2012 at many sites, including Milwaukee and Flint. We will see if O'Hare can tick up to 97F and that would also be the case there. We have seen a couple of warmer episodes in August (perhaps June?), but this will be the hottest July temperatures in 14 years at a number of sites.

MKE was 97F at the last METAR observation. Up to 98F/99F now, per 5 minute observations. Last ob was 99F. Due to rounding probably only 98F, but definitely above 97F.

Looks legit by the way, maybe a tad warm. Checked PWS stations around there and most were in the 100-103F range, even right to the shore.

Wow! 104F now. Really mixing well there - downsloping effects? Dews are cratering with gusty west winds.

Up to 102F at Oscoda, Michigan. Toronto, Ont. was up to 97F at the top of the hour.

Looks like a smokemaggeddon scenario on Wednesday if the HRRR is right?

Wow, this looks quite bad.

Will have to keep a close eye on the path of this wildfire smoke. RAP suggesting some surface smoke on Wednesday, densest near the fires, but extending across the Great Lakes.

Looks like maybe more surface smoke on Wednesday if the RAP is correct. Will have to watch out for this, as this could hold back high temperatures some.

Looks like most of it stays aloft tomorrow.

Going to be getting real smoky soon.

This is absolutely relevant to the ENSO discussion. U.S. weather is influenced by El Niño, and this entire thread is speculating about what it may mean for winter. But it is summertime right now, Niño 3.4 anomalies are already off the chart, and SST anomalies are nearing strong El Niño territory. The possible effects do not wait for December to begin.

Incidentally, contemporary observers in 1936 did not simply pretend weather history began with the official national series. So I highly doubt anyone in 1936 was objecting that it was not really the hottest because the national record did not reach back to 1776. The chief of the Iowa Weather and Crop Bureau described July 1936 as the hottest in at least 117 years, drawing on regional observations extending back to 1819. The official CONUS record begins in 1895 because that is when coverage becomes adequate for a consistent national average — not because no weather observations existed earlier. We have scattered instrumental records from the eighteenth century and a rapidly expanding national network by the mid-nineteenth century. No, we cannot calculate an apples-to-apples CONUS average for 1776. But given the magnitude and enormous geographic footprint of July 1936, it is exceedingly difficult to believe that a still-hotter national July occurred in the preceding century without leaving a conspicuous instrumental and historical trail. “Hottest on record” is entirely correct — and 1936 was very likely exceptional over a considerably longer period.