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| "Corn sweat" is making a spell of heat and super high humidity in the Midwest even worse. A squirt of that steamy air is due here in Vermont/New England at the end of this week. |
Sinking air under the high pressure will compress the air, heating it up. The hot sun will add to it. Weak winds from the Gulf of Mexico and Atlantic Ocean will turn the air disgustingly humid over wide areas of the Midwest.
Heat warnings and advisories today extend from South Dakota and Minnesota southward along a roughly 500 mile wide band sort of following the Mississippi River all the way to the Gulf Coast.
The heat index could reach 110 degrees or higher in some areas under the heat alert. It's nasty.
The actual temperatures generally won't be near record highs, but the dew points, a rough measure of how humid it is and how much moisture is in the air, will be as high as they can get.
The timing of this heat dome could not be worse, because, something called "corn sweat" will make the humidity in the U.S. agricultural belt even more oppressive and dangerous than it otherwise would be.
The Washington Post describes it this way:
"Like a person breathing, corn exhales water vapor through its leaves - a process called evapotranspiration - which exacerbates humidity in agricultural regions during the summer."
.........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 to tasseling and pollination, when the flower emerges from the corn stalk."
Under the corn sweat-saturated heat dome, some areas of the Midwest could see dew points near 80 degrees, something you often see along the Gulf Coast in July, but not nearly as often in places like Illinois or Iowa. But, occasionally, during corn sweat season, it gets that bad.
The high humidity, aided by this corn sweat, could help add to the long list of destructive flooding events we've had in the U.S. this month.
Weather disturbances moving along the northern periphery of the heat dome will tap into that incredible reservoir of humidity and touch off the risk of flash flooding in the Great Lakes region over the next two or three days, and possibly in parts of the Northeast toward Friday or Saturday
VERMONT EFFECTS
This morning was pretty cool, with most of Vermont down in the 40s, as expected. There might have been some upper 30s in a couple spots in the Northeast Kingdom, based on reported readings of 35 degrees in Saranac Lake, New York, and 38 degrees in Whitefield, New Hampshire. The Champlain valley stayed above 50 degrees.
One note to demonstrate how climate change has altered "normal." In the century ending in the 1980s, Burlington would get into the 40s on at least one or two July nights most years. That began to gradually change in the 1990s. Including last night, Burlington has not had a July morning under 50 degrees since 2015.
That's not to say it will never be in the 40s on a Burlington July night again, but climate change has been one factor in keeping summer nights warmer than they once were.
Today and tonight will remain cool. More sunshine than yesterday will help boost today's highs well into the 70s. Still a little below normal for this time of year but still nice. Most of us will get down into the 45 to 55 degree range tonight.
Winds will gradually shift and come from the west and southwest, eventually bringing that hot, and very humid air - aided a little by that corn sweat - into New England Thursday into Friday.
Wednesday will be warmer, and by Thursday, it's full steam (literally!) ahead with the heat and humidity. It should make it to 90 degrees or more in many Vermont valleys Thursday and possibly Friday.
We'll have to watch the first in a series of weak cold fronts that could touch off some strong thunderstorms either Thursday night or Friday.
A series of weak cold fronts will continue to gradually temper the heat, though it probably will stay warmer than normal into the early part of next week,
After that - as we've been saying for days - that heat dome will shift west, probably keeping New England on the cooler side as we get to August.
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