TheClimateChanger

Minneapolis has done quite well in the heat department for the end of summer and early autumn. August A significant heat wave in late August brought numerous hourly monthly heat index records. Hourly data only going back to 1945 - all from MSP. It was only the 4th year to have multiple days at or above 98F in the month of August: The low of 79F on August 23rd was the 6th highest on record, missing the monthly record of 80F (which has been set 5 times) by 1F. The mean temperature of 88.5F on the 23rd was the 4th highest ever observed on any day in the month of August (chart below lists third, but there were two instances of 89.0F in 1947). The only higher are 89.5F, on 8/6/2001, and 89.0F, on August 4, 1947 & August 5, 1947. September September 2023 was one of only 6 years to have 2 days at or above 97F, in the threaded record. It was the first time that has occurred since 1939. It was also one of only 6 years to reach or exceed 98F in the month of September, and the first time that value has been reached since 1976. The daily mean of 86.0F on the 3rd and the 4th tied for 3rd highest daily mean ever observed in the month of September in the threaded record (chart below lists third, but there were two instances with a warmer daily mean in 1931). The low of 75F on September 3rd tied for 4th highest observed, and tied 2002 & 2015 as the highest since 1953. The only higher minima were 77F on September 5, 1912 & 76F on September 2, 1953 & September 9, 1931. Looking at hourly temperature readings at MSP back to 1945, 16 hours set or tied the highest observed in the month of September. October The high of 92F on the 1st is the highest maximum temperature ever observed in the month of October. It was also only the third occasion where the temperature has reached 90F in the month of October. The low of 69F on the 1st tied for 4th highest ever observed in the month of October, behind October 8, 2011 (71F), October 6, 2007 (70F), and October 3, 2005 (72F). The mean temperature of 80.5F on the 1st broke the monthly record by 2F: 9 of 24 hourly temperature records for the month of October (since 1945) were set yesterday:

Incredible. Closer to home, there were quite a few October monthly records - highest recorded maximum and/or minimum temperatures for the month - over the Midwestern U.S. yesterday. They've had some pretty impressive late season heat this year - with record-breaking heat indices for the month of August, and in some cases, all-time, in late August; a major heat wave in early September, which broken many daily records and approached/exceeded monthly records in some spots, and now an impressive heat spell here to begin October. It hasn't translated east much, however.

Some other notable records from Minnesota. 91F, at St. Cloud, is a new daily and monthly record. The prior monthly record was 90F, set on October 2, in 1992 & 1953. Prior to today, the latest day to exceed (not just reach) 90F was September 22, 1936, when it reached 92F. 89F, at Brainerd, is a new daily and monthly record. The prior monthly record was 88F, set on October 2, 1992. Brainerd has been no stranger to anomalous, out-of-season heat in recent times. Just last month, it reached 102F on September 3rd, which was only the 2nd time it has reached into the triple digits in the month of September, and was just 1F shy of the September monthly record of 103F, set on September 10, 1931. Brainerd hit 100F on June 4, 2021, and on June 20, 2022, which are two of only three 100+ days in the month of June (the other being the 100F reading on June 19, 1988). The only earlier 100F+ was May 31, 1934. 83F, at International Falls, tied the daily record but was well shy of the monthly mark. Still only 5 days in the month of October have eclipsed that reading - 87F, on October 2, 1912; 86F on October 2, 1953; 88 on October 5, 1963; 84F on October 5, 1970; and 88F on October 11, 2015. 90F, at Rochester, set a new daily record but was a few degrees shy of the monthly record. Still it was one of only four 90F+ days ever observed in the month of October - the others being 93F on October 3, 1997, and 90F on October 2, 1953, and October 9, 2010. It is the latest in the year for two consecutive 90F or better readings, however. Wisconsin also had some notable readings. The 88F reading at Green Bay tied the monthly record set on October 6, 1963. LaCrosse reached 91F, which while 1F below the daily record, is notable as only the 4th 90F+ reading on record there.

Minneapolis actually reached 92F today, which as noted is the new monthly record, and only the third reading at or above 90F in the month of October. Prior to today, the latest date in the calendar year on which it reached or exceed 92F was September 22nd, when it reached 95F in 1936 & 94F in 2017.

Some other noteworthy readings from Iowa, from sites with threaded records dating back to the 19th century. It reached 91F at Cedar Rapids, setting a daily record. This is only the 11th day on record in the month of October to reach or exceed 90F, and the first since October 3, 2006. Only three days were hotter - 94F on October 3, 1997; and 92F on October 2, 1953, and on October 6, 1963. Waterloo, Iowa reached 93F, setting a daily record. Only three days in the month of October have been hotter - 95F on October 3, 1997; October 6, 1963; and October 12, 1930. It was also the first time it has reached or exceeded 90F in the month of October since the 95F reading on October 3, 1997. Des Moines reached 91F, one shy of the daily record. However, it was only the 13th day in the month of October to reach or exceed 90F, and the first since it reached 92F on October 3, 1997.

Reached 95F at Spencer and Oskaloosa, Iowa, just a couple degrees below the statewide record high of 97F for the month of October, set on October 3, 1938, at Onawa; October 4, 1938, at Knoxville; and October 5, 1963, at Forest City and Shenandoah. The high of 95F at Spencer, broke the daily record by 4F, and also eclipsed the prior monthly record of 93F, set on October 2, 1997 and October 5, 1963. Spencer has now reached 95F or better on three consecutive days. Looking through the records, the latest stretch of 3 consecutive days at or above 95F, was September 12-15, 1939, when it exceeded that mark on 4 consecutive days. It also looks like last year had some notable late season heat at Spencer, Iowa. It reached 101F on September 20, 2022, which was the latest 100F reading on record by a week. The prior record was 100F on September 13, 1939, during the aforementioned 4-day stretch of extreme heat. That reading is the only other reading of 100F or better after September 4th. Records at Spencer date to 1895.

Per Maximiliano Herrara on X, the Iowa state record high for October is 97F. I saw a couple sites reached that today on the state roundup and he indicated temperatures as high as 99F may have occurred near the Nebraska border.

Also, looking at the table, only 10 days have ever reached or exceeded 90F at Cedar Rapids in the month of October: October 1, 1976 (90F); October 1, 1897 (90F); October 2, 1953 (92F); October 3, 1997 (94F); October 3, 2006 (90F); October 3, 1897 (90F); October 4, 1938 (91F); October 4, 1897 (90F); October 6, 1963 (92F); and October 10, 1962 (90F). Three of those dates were in 1897, so only 8 unique years since 1893. While 94F seems unlikely at KCID tomorrow, 90F is certainly possible. Fairly rarified air for October, should it reach that temperature. Would be only the 11th 90+ day on record in October, and 9th year to reach 90F or better in the month of October (and first since 2006).

Wow! Very impressive reading. Breaks the daily record by 3F. Dating to 1893, only one year had a later reading of 94F or better - 1997, when it reached 94F on October 3. Obviously, that means had it reached that temperature on tomorrow's date, it would have tied a monthly record for October.

Well, maybe sobering was too dramatic of a word. Certainly, the warmer minima are a blessing for farmers completing their fall harvests. With that said, it does raise important questions about the speed and extent of the environmental changes occurring since the plant and animal life in a region may have evolved in a manner that depends on frosts or freezes occurring by a certain date, or temperatures reaching a certain level of coldness over the winter [i.e., potentially to kill off parasites, which may harbor disease]. Although just outside this subforum, if we look at Hagerstown, Maryland, we see sub-40F lows in the month of September are now rarer than subfreezing lows were historically. That's a significant change. Since 2000, only year has had a low temperature less than 40F (2020, when it dropped to 38F). Conversely, 19 historical Septembers had lows at or below freezing. However, this has not occurred since 1974. Whereas in the 2010s, three separate years had absolute minima in the 50s, in the 1940s, three separate years saw minima in the 20s. Warmest absolute monthly minima Coldest absolute monthly minima [showing all years at or below the freezing mark] Like central Pennsylvania, many past years had mean monthly minima less than the coldest temperatures observed in recent years. In fact, if we look at 2018's absolute low of 54F at Hagerstown, fully 52 years had mean minima less than or equal to this value in the month of September. And allowing for rounding, fully 57 years had mean mimima less than 54.5F.

With a couple days left in the month, cold air has been lacking in many locations in New England with absolute monthly minima in several locations among the warmest of record. The warmer nights are certainly a blessing for farmers completing their fall harvests. Burlington, Vermont Mount Washington, New Hampshire Caribou, Maine Worcester, Massachusetts Some of these locations have observed several Septembers where the monthly mean low temperature was roughly the same as or colder than 2023's absolute coldest night. Most notably, the year of 1963 saw a mean low at Burlington, Vermont of 40.2F, or nearly 5F colder than 2023's coldest of 45F, and also a mean monthly low of 46.9F at Worcester, Massachusetts, a little more than a degree less than 2023's coldest of 48F. Burlington, Vermont Worcester, Massachusetts

I've been following this for awhile, and it's been interesting to see the dense smoke interacting with the lower sun angles over the high latitudes. Nuuk, Greenland was very dark at midmorning a few days ago, and I saw many in Atlantic Canada observed strange, pale sun through the nearly opaque layer of smoke. Even in the UK, the sun has been significantly dimmed behind the pall of smoke. I wonder if the limited solar radiation will help to promote some early season cold air masses.

Looking at graphs like this, it should be apparent that this is Canada's version of Australia's Black Summer of 2019-2020. Will be interesting to see whether this results in a miniature volcanic winter in the Northern Hemisphere. Smoke from Australia's Black Summer fires are known to have cooled the earth, particularly in the southern hemisphere, and possibly increased the chances of that multi-year La Nina: Smoke from the Black Summer wildfires in Australia impacted climate, high-altitude winds of the Southern Hemisphere (phys.org) A recent study found wildfire smoke and volcanic emissions have offset 20% of the warming which would have otherwise occurred since 2015: Smoke from volcanoes and wildfires have a parallel cooling effect, but it won’t do much to quell global warming | Enterprise Will be interesting to see whether this has any sort of lasting impact on the global, or regional, climate. For the record, there have been a number of intense outbreaks of pyroCb sufficient to loft a significant quantity of soot and smoke into the lower stratosphere over the course of the summer.

Elkins, West Virginia Warmest Absolute Low Temperatures Coldest Monthly Mean Minima Wow!

Man, I'm a sucker for statistics. But even I am taken aback sometimes. It's crazy seeing how the coldest temperatures observed in many locations for the entire month of September in recent years are now sometimes roughly the same or even warmer than the mean monthly minima from many historic Septembers. I know many of you said people don't care about low temperatures, but to me stuff like this is just plain sobering to see. It's like this at many places too. Harrisburg - warmest absolute monthly minimum temperatures [Note: It dropped to 50F today, which is not yet reflected in this] Harrisburg - coldest mean monthly minima

Grand Forks has dropped as low as 36F this month, which, should it hold, ties for third warmest monthly minimum behind the 40F lows observed in September 2021 & 2019. However, in 1893, the low temperature was as cold as 11F on the 27th, and 14F on the 26th, just to give an idea of how cold it can be this time of the year in the upper Midwest and northern Plains. Many a hardy palm tree would have perished in the September 1893 cold snap, I would think. Interestingly, quite a few historic Septembers in Grand Forks had mean monthly minima roughly the same, or colder than, the absolute coldest September low temperatures in several recent years.

With only a couple days left in the month, it appears almost certain that many areas in the Midwestern United States will see one of the warmest absolute minimum temperatures ever recorded in the month of September in 2023. The lack of any early season cold is a blessing farmers and sensitive plants (including hardy palm trees). Minneapolis, Minnesota Chicago, Illinois Milwaukee, Wisconsin Des Moines, Iowa Grand Forks, North Dakota Marquette, Michigan

And yet we have these crazy yinzers on Reddit who think it’s some sort of achievement not to run the heat by October 1: https://reddit.com/r/pittsburgh/s/1ePk1TxQI5

Purple sun over Atlantic Canada today from dense wildfire smoke aloft.

Interesting pattern. Unless the Canadian wildfires are under control by then, dense smoke looks possible as well.