Here is an annual average comparison series.
The difference is generally quite small, thought there is a bit of systematic shift, especially in the early period. This is mostly related to changes in how interpolation/extrapolation is being done, though the source data has increased a bit too.
Comparison maps over California of annual average temperature anomalies in the year 2022 from the low-resolution and high-resolution versions of Berkeley Earth.
Comparison maps over California of annual average temperature in the years 1951 to 1980 from the low-resolution and high-resolution versions of Berkeley Earth.
The transition last year from the old @berkeleyearth.org temperature analysis to the new high-resolution version doesn't make much difference for the global averages, but it is really useful when it comes to capturing local and regional details that would otherwise be missed.
Not the main point of the thread, but the Berkeley Earth to ERA5 comparison is interesting for another reason.
ERA5 Reanalysis is generally very good, but it has some regional issues with long-term drift, likely due to changes in its inputs, especially prior to satellites.
Anyway, this is just an aside. For a longer discussion of the March USA heatwave, see my previous thread.
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In general, that's because it is physically easier to have large temperature swings in colder months.
How impactful a heatwave is depends strongly on context. Large swings are more common in cold months, but smaller swings in the warmest months can have greater consequences.
The Dust Bowl heatwaves and drought was more impactful than the recent March heatwave for several reasons.
However, as with Centerville, the summer Dust Bowl heatwaves generally involved temperatures 25-30 °F (14-17 °C) above normal, less of a swing than the recent March event.
Centerville is interesting for another reason.
It's an example of a weather station whose all-time record high was set during the Dust Bowl. A reading of 113 °F (45 °C) in July 1934.
Many long-term stations still carry records from the Dust Bowl heat waves of the 1930s.
Time series of daily max temperature in Centerville, South Dakota for each year 1905 to 2026.
The March heatwave in the USA set many impressive records. 21 weather stations recorded daily temperatures at least 40 °F (22 °C) above normal.
For example, Centerville, South Dakota reached 93 °F (34 °C) on a day when the normal high would be 49 °F (9.4 °C).
The thread contains a variety of charts.
However, assuming that you are asking about the first map, that's the temperature anomalies (in degrees F) on a single day around the peak of the heatwave.
Time series plot showing the regional mean of TMAX in the Western USA for the hottest March day of each year 1940 to 2026. Data from ERA5. Historical statistical estimates of the evolving probability distributions are also shown. The warmth in 2026 and the relative cold in 2023 appear as stark outliers
A chart like this, with its suggestion towards increased variability, is the kind of thing that can keep climate scientists up at night.
Complex & unexpected shifts in dynamics can be deeply troubling, as they may give rise to extreme events beyond what anyone anticipated.
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Is the March heatwave simply an extreme fluctuation from trend?
The kind of event that, though rare, will naturally occur by chance every few hundred years.
Or is it hinting that fluctuations of this magnitude will be more common in a warmer world?
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A few years of data isn't conclusive, but the recent events in the Western USA strongly suggest that we may be looking at increased temperature variance in this region (at least in March).
And statistical models trained on past variability may be ill-prepared for that.
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Times series plot showing the regional mean of TMAX in the Western USA for the hottest March day of each year 1940 to 2026. Data from ERA5. Historical statistical estimates of the evolving probability distributions are also shown. The warmth in 2026 and the relative cold in 2023 appear as stark outliers.
However, the Western USA in spring might be an exception.
When we look at daily temperature extremes in this region, the long-term trend is clearly positive, but recent years have provided extremes in both directions, high *and* low.
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In climate change, we often talk about the increasing variability of precipitation (i.e. more floods & more droughts).
However, when it comes to temperature, clear examples of changes in variances are rarer. Often, the mean increases, but the variance remains similar.
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Three panel image from the IPCC showing examples of how climate distributions can shift due to changes in mean, in variance, or both.
In more concrete terms, sometimes global warming brings with it not just a change in the local mean, but also a change in the variance.
When weather patterns shift in ways that alter the variance, the frequency of extremes can change in ways that are hard to predict.
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The climate scientist @katharinehayhoe.com is fond of the phrase "global weirding" to denote ways that global warming also leads increasingly strange and unpredictable weather.
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But are those statistical models (in this case based on generalized extreme value theory) still reasonable in the changed modern climate?
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In the modern climate, boosted by global warming, the March heatwave in the USA is still extraordinary.
The kind of heatwave that should occur no more than once every few hundred years.
Without global warming's boost? The typical statistical models say this would have been impossible.
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As extreme as it was, we are somewhat lucky that this heatwave occurred in March rather than June or July.
Water and ecological disruptions are unfortunate, but a similar heatwave in summer would have brought a significant body count.
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Image from the New York Times showing USDA data on the snow pack depth in areas feeding the Colorado River. March 2026 is the lowest on record.
The US heatwave melted much of the already thin mountain snow cover, leading to a snowpack that is the lowest on record across much of the Western USA.
This will undoubtedly lead to reduced water availability for agriculture and other uses in coming months.
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Though the recent US heatwave occurred in March, it calls to mind the extraordinary heat dome and heatwave that affected the Pacific Northwest in June 2021 and shattered Canada's National Temperature Record.
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US Drought Monitor map for March 24, 2026.
Temperatures during the heatwave were also boosted somewhat by preexisting low soil moisture in the US West due to low rain/snow during the recent winter and the resulting drought across much of the region.
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Map over North America of March average temperature anomalies from CDAS showing the US heatwave and relative cooling over Northern Canada and Alaska.
As is common with heatwaves, warmth in one area was balanced against relative cooling in other areas.
In this case, cooling occurred over Canada and Alaska. This also included some local record lows, though not as extensive or extreme as the highs observed in the USA.
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Map of atmospheric pressure anomalies over North America for March 19, 2026, showing the high pressure system that built the heat dome / heat wave.
Very roughly, a persistent high pressure system over the Western USA was related to a blocking pattern that brought clear skies and large-scale warmth over the USA and associated cooling over Northern Canada and Alaska.
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So, what is going on here? How did such an extreme heatwave come to be?
The immediate cause is mostly down to weather, i.e. variations in atmosphere circulation and an extreme heat dome.
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Plot showing for each year 1940 to 2026 the daily TMAX averaged across the Western USA. The year 2026 is highlighted as well as the expected daily mean.
Averaging across the whole Western USA helps to further reveal the scale and severity of this heatwave.
This heatwave, with a daily regional average +23 °F (+12.7 °C) above normal, is far more extreme than anything previously seen in this large region at any time of year.
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Same as the previous image, but only showing record fractions for March.
Such a widespread and extreme heatwave has no previously recorded analogs at all in the USA during March.
Almost 1/3 of US weather stations set new monthly records. In no previous March did more than 10% of stations simultaneously set a record.
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Time series from 1925 to 2026 showing the fraction of active us weather stations that set a new monthly record for the warmest daily max temperature. Only stations with at least 30 years of prior observations at the time being considered are included.
The scale of the heatwave was so extreme that almost 1/3 of active US weather stations set a new record for their locally warmest day in March.
The only other time such a large fraction of stations simultaneously set new monthly records was during the Dust Bowl.
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Histogram showing the number of active US weather stations that borke their monthly record in 2026 by the amount of the new record.
Usually, when we see new records for the warmest day in a particular month at long duration weather stations, it is by a small margin, but this time around hundreds of stations broke their previous record by 2 or more degrees (F).
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Time series of daily TMAX for each year in Sedan, KS from 1893 to 2026. The year 2026 is highlighted, showing extraordinary warmth.
In March, ten stations were so warm that they would not only beat their April record but would also beat or tie their record for the warmest day ever observed in May.
In Sedan, Kansas, the 100 °F (37.8 °C) on March 22, 2026 was two months before the previous earliest 100 °F.
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