The main purpose of this ongoing blog will be to track planetary extreme, or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials).😜
Main Topic: Update on Heatwave Pemex
Dear diary. It’s only been a few days since I declared that we had a new major U.S. heatwave on our hands:
Pemex has grown into a mid-range CAT3 system that is typical for most summers, but the forecast longevity of the heatwave plus the fact that it will grow will peg this beast as a climate changed phenomenon.
Here is the current state of watches and warnings:
Pemex is taking over the Plains and Southeast and is making inroads across the Midwest. The system has not set many daily high max records so far and probably won’t set many in the future. What will make life miserable for millions will be a myriad of high minimum records set from Pemex.
The heat dome in association with Pemex will fall then peak between 593 to 598 decameters during the next two weeks and oscillate between the Southeast and Rockies during that period:
We will see how well that last panel verifies in August. Should it come close, we will have another historic CAT4 on our hands.
Here are more details about Heatwave Pemex from the Washington Post:
https://www.washingtonpost.com/weather/2025/07/21/corn-sweat-humidity-heat-wave-forecast
Corn sweat will intensify a heat wave this week
Heat index values will surge toward a dangerous 115 degrees in the central United States this week due to the combined effect of corn sweat and a heat dome.
Updated July 21, 2025 at 9:25 a.m
Fresh-picked corn in Franklin, Va. (Kristen Zeis/For The Washington Post)
By Ben Noll
July has already been more humid than average, and now another, less obvious factor will enhance humidity this week: corn sweat.
Like a person breathing, corn exhales water vapor through its leaves — a process called evapotranspiration — which exacerbates humidity in agricultural regions during the summer.
In the week ahead, some of the country’s most oppressive heat and humidity will be found in the Corn Belt, an area of the United States that stretches from the Dakotas to Ohio, sending heat index values toward a dangerous 115 degrees. States such as Missouri, Minnesota, Iowa, Indiana, Illinois and the Dakotas are forecast to have humidity levels that rival or exceed Florida’s.
According to Iowa state climatologist Justin Glisan, this is the time of the year when humidity contributions from corn sweat are highest — around the time of tasseling and pollination, when the flower emerges from the corn stalk.
He described the phenomenon as being thick and oppressive, particularly if there is no wind — “like being fully clothed in a sauna or steam room.”
Humidity will surge to extreme levels across the Plains and Midwest this week because of a heat dome and corn sweat. (Ben Noll/Data source: ECMWF)
The unique pattern will add to a brutal wave of humidity and heat developing this week, one that will start in the southern and central states and then expand into the Northeast and Mid-Atlantic, where temperatures could reach 100 degrees on Friday.
Where and when it will be hottest
A heat dome over the South will expand into the Midwest by midweek and reach the East late in the week.
The combined effect of the corn sweat and the heat dome, which will draw up hot and humid air from a warmer-than-average Atlantic Ocean, will exacerbate the risk for heat-related impacts in the Plains and Midwest. Heat advisories, watches and warnings cover hundreds of counties across the country.
Here’s a day-by-day outlook of the heat:
There’s a major risk for heat-related impacts across many states this week as the combination of very high humidity and high temperatures cause heat index values to surge. (Ben Noll/Data source: NOAA)
Monday
On Monday, the most dangerously hot and humid conditions will stretch from the South to the Plains — with the cities of Tampa, Atlanta, Memphis, Nashville, Omaha and Wichita having a major or extreme risk (Level 3 or 4 out of 4) for heat-related impacts according to NOAA.
Tuesday
Extreme humidity is expected to reach the Corn Belt on Tuesday, when heat index values reach as high as 110 degrees.
Places including Omaha; Des Moines; St. Louis; Kansas City, Missouri; Lincoln, Nebraska, and Sioux Falls, South Dakota, all have a major risk for heat-related impacts.
Wednesday
High heat and locally extreme humidity will surge into the rest of the Midwest and western Great Lakes on Wednesday, reaching Chicago, Milwaukee and Green Bay, Wisconsin.
In Chicago, there’s an extreme heat watch in effect for Wednesday and Thursday, with heat index values forecast to range from 105 to 115 degrees.
Thursday
Extreme humidity and heat will remain in place over the Midwest on Thursday, while advancing eastward into the eastern Great Lakes and Ohio Valley, affecting Chicago, Detroit, Indianapolis, Cincinnati, Cleveland, Pittsburgh and Buffalo.
Friday
High heat will surge into the Northeast and Mid-Atlantic on Friday, where temperatures could push toward 100-degrees in a few locations.
Meanwhile, there will be little relief from the heat in the Midwest and Great Lakes, including southern Canada.
With very warm nights expected this week, more than 100 overnight temperature records may be approached or broken, mostly in central and eastern states. (Ben Noll/Data source: NOAA)
Due to the unrelenting humidity, more than 100 overnight temperature records are forecast to be challenged this week, mostly in central and eastern states.
This is consistent with the trend of overnight temperatures increasing at a faster rate than daytime temperatures amid a warming world, which increases heat stress for people, pets and plants.
Possible impacts of continued heat
For central states, the unusually hot, humid and downpour-laden pattern shows no signs of letting up into early August.
Most of the central and eastern United States is not experiencing a drought, while many western states are. (Ben Noll/Data source: NDMC/USDA/NOAA)
While drought coverage is currently sporadic across the Corn Belt, the combination of excessive humidity, moisture and record warm overnight temperatures introduces other concerns.
Warm nighttime temperatures can increase respiration in crops, the process by which plants convert sugar into energy. This can result in the loss of energy that could have otherwise increased crop yields, said agronomist Megahan Anderson with Iowa State University.
In Iowa, the state with some of the highest corn-producing counties in the nation, Anderson said a potpourri of diseases also affects corn. Though the overall level is low, the conditions don’t help.
“We are set up in a way that disease could easily spread regardless of temperature, as long as humidity, extended periods of dew on leaves and/or rainfall continues,” Anderson said.
By Ben Noll Ben Noll is a meteorologist passionate about explaining the why behind the weather, extreme events and climate trends. He has expertise in data analysis, supercomputer-driven graphics and forecasting weather worldwide. follow on X@BenNollWeather
Here are more “ET’s” recorded from around the planet the last couple of days, their consequences, and some extreme temperature outlooks, as well as any extreme precipitation reports:
Here is More Climate News from Monday:
(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity. In most instances click on the pictures of each tweet to see each article. The most noteworthy items will be listed first.)