TheClimateChanger

Here's what Lansing, Michigan (one of my reference cities for data back to 1863) looked like in July 1865, just to get a flavor of some of these months: Conversely, here is July 1868 at Lansing:

Here is my chart for the lower Great Lakes region for the month of July. Top 5 warmest years: 1921, 1868, 1955, 2012, 2020 Top 5 coolest years: 1891, 1865, 1841, 1842, 1837

Unreal how it's only a fraction of a degree warmer than DTW despite basically being in Kentucky.

Not gonna lie. This would be pretty epic.

Thought we might make a run at 90 today, given it was 87 before 1 pm. Looks like clouds and isolated showers will prevent that from happening.

Lots of red and orange on this map.

Will be interesting to see whether Dayton accumulates another 90 degree day today. 5-minute observations show a number of 90F readings, but, due to rounding issues, that does not guarantee a high of 90F.

On 90-degree watch today. Up to 88 on the 5-minute observations. Can we eek out the third 90+ of the year?

Sorry, for off-topic, but I wasn't the one who brought up Chile. Just for additional context, here are the records for La Serena, Chile in the Coquimba region where the heat has been most pronounced. While average highs are lower this time of the year, some of the warmest readings on record have occurred in the wintertime. In general, it's a very temperate location that has never exceeded 28.5C. So while the intensity of the heat is very impressive, and perhaps unprecedented, the fact that it's occurring in the middle of winter is not particularly noteworthy. These areas do not experience winters like we do here in the United States. Instead, it's only a little bit cooler than summertime but with more daily variability.

I don't think those areas have nearly the seasonal variations that we do. Nevertheless, some areas have reached all-time record highs, so it is certainly way out of the norms either way (as evidenced by those ECMWF maps showing 20C + anomalies in spots). It appears some of the extreme warmth is being driven by Foehn winds, also known as Chinook winds in North America (i.e., extreme compressional heating downwind of the mountain peaks).

Unofficial data for the period 1830-1870 is available in the 1943 Annual Weather Review for MDW. It is based on records of the War Department at Fort Dearborn on Wacker Drive in present-day downtown Chicago, records of the Smithsonian Institution in various parts of the city, with some interpolation of missing data by other observations outside the city. Note that temperature means during this era were generally taken as the average of three measurements (typically 7am, 2pm, and 9pm), which tends to have a small warm bias compared to the average of maximum and minimum. This warm bias is most significant in the summertime. Recall this predates daylight saving time, and time zones, at least in the early part of that period. So these would have actually been observed after 8 am in the summertime [perhaps as late as 8:30, 8:45 if prior to standardized time zones], and would have been several degrees above the actual low. The inclusion of the 9 pm [actually equivalent to readings taken at 10 pm or later in the summertime during modern daylight saving time] reading somewhat mitigates this effect, but does not entirely eliminate it.

You can always pull up the station histories from the monthly and annual weather reviews under Local Climatological Data (LCD) on the NCDC Image and Publication System: https://www.ncdc.noaa.gov/IPS/lcd/lcd.html These also tell exactly when the extreme thermometers were replaced with hygrothermometers, as well as the elevation of all of the instruments above ground level (and the elevation of the observation site above sea level). For example, here is the station history in the 1979 annual summary for MDW: And in the 1987 annual summary for ORD:

Very impressive. From Dr. Spencer:

July temperatures at Grand Canyon National Park Airport and Phoenix, from 1996-2023. There may be a small UHI component to the warming trend, but it's still clearly warming very rapidly even in places where nobody lives. Grand Canyon N.P. - Warming at 9.9F/century since 1996 Phoenix - Warming at 12.2F/century since 1996

Not sure yet where June & July two-month period will fall, but Ryan Maue says July will be 10-12th warmest in the rankings nationally. Looking at the list, only 1936, 1934, 1901, 1931 & 1980 were the only pre-21st century years with hotter Julys than this year nationally.

And holy cow - a 35C diurnal temperature range. Wow.

All time high for Coquimbo province, in the middle of winter:

Yes, primarily aloft today. The NWS Pittsburgh AFD does, however, suggest some may mix down to the surface tomorrow. Not sure if this will impact central PA though.

Doubtful. You observed only a 13.7F diurnal range in July. That has to be the smallest diurnal range on record, no? I would argue that is an unnatural climate for anywhere in Pennsylvania. Even adjacent to Lake Erie, the diurnal range in Erie is typically larger than that. Philadelphia, in the core of the urban heat island, had a diurnal range of 16.7F. I have my doubts that a diurnal range that small is possible in a summer month in Pennsylvania, without some sort of external influence on the temperature.

Those fires in western Canada probably won't be out until winter settles into the region. Regardless, another couple of bonus gray days courtesy of our friends up north.

No problem. Thank you for compiling all of that data. Not a lot of people from that region on this forum, but those are some incredible numbers.

Doubtful. I have been looking into this stuff for decades, and have never seen a "volcanic summer" type effect ever noted in the scientific literature. Is there a single known or posited case of a submarine volcano having a substantial warming effect? I don't doubt the possibility of a small effect, but a large one? To be clear, I'm aware there are instances of warming attributed to the greenhouse gases emitted from large eruptions or a series of eruptions (flood basalt) but such warming occurs over a substantial period of time. In the immediate aftermath of these eruptions, there would be periods of volcanic winter.

Good post, Don. Just a few comments: (1) I believe Table 4 contains an error in the reported mean monthly minima for the 30-year periods ending in 2000, 2010, and 2020. To be specific, the values appear to be 10 degrees too high for each of those periods. (2) The numerous records from the late 1980s to mid 1990s should be considered suspect due to the use of the HO-83 hygrothermometer, which imparted a known warm bias, especially under full sun and light wind conditions. Nearby Tuscon, Arizona set a large number of records during that era, which were considered to be inflated. There was a New York Times story about it at the time. I don't think we should toss records due to equipment biases; however, it does tend to put things even more into perspective. You can liken that era to the steroids era in baseball. There were certainly some hot years, but some of the extreme records were probably somewhat inflated. To continue with the baseball analogy, the current stretch would be like if someone, or several players, not taking steroids, suddenly starting knocking 80, 90 balls out of the park each season for several years in a row. So, anyways, it is interesting the two highest readings - 122F and 121F - both occurred during that period. Given the known bias, it wouldn't surprise me if it really was no more than 119F on those dates. (3) If 2020 was a taste of summers to come in 2050, what year does this equate to? Perhaps, it's already here and things are progressing faster than expected in some spots.