Tuesday, 11:59 a.m.
We're at the peak of summer heat right now. From this point forward in most places across the country, the average temperature begins to fall - slowly, imperceptibly at first, but there's no turning back as the amount of daylight steadily decreases in the Northern Hemisphere. It's a time of the year when the jet stream is tightening to its northernmost point, usually, with a lot of warmth spread across the nation.
I say 'typically,' because this month has been anything but typical. We began the month with unrelenting heat in the Northwest that has no doubt contributed to some of the wildfires burning in Washington. Then, just last week, the dreaded 'polar vortex' came swooping down into the Midwest and across the Great Lakes to bring record lows to much of the country up and down the Plains states into the East.
That vortex has come and gone, and heat has returned, this time over the eastern Rockies and western Plains. Look at the highs from Monday:
Some of this heat will get a haircut over the next 24 hours thanks to a hard-charging cold front blasting out of the northern Plains and through the Midwest. This front means business, having sparking some intense thunderstorms that brought nearly 3 inches of rain to Grand Forks, North Dakota, overnight. More severe thunderstorms will blossom this afternoon ahead of this front across parts of the Midwest and into the Great Lakes:
As this front pushes across the Great Lakes into New England and over the Appalachians into the mid-Atlantic states tomorrow, it will help to squeeze the heat into the East. Up to now, the air aloft just hasn't been terribly warm, and there's been sufficient moisture in the lower half of the atmosphere to generate enough clouds to keep temperatures in check. Tomorrow we'll take the lid off, as the heat will come in over the top, you might say, summoned by the approaching cold front. Look at the 12z July 22 GFS 6-hour, 2-meter maximum temperature forecasts for tomorrow afternoon ahead of the front:
This will kick up another round of strong to potentially severe thunderstorms before the front passes through the mid-Atlantic states, then comes more or less to a grinding halt Thursday and Thursday night.
Back to the West, the upper-level ridge over the central and southern Rockies is still holding strong on Thursday:
That means the heat will continue over Colorado, New Mexico, Kansas, Oklahoma and Texas. Farther northwest, a vigorous upper-level low, seen Thursday evening in the image above over southern Alberta, but much stronger now just off the coast of Vancouver, will roll over the top of this ridge and flatten it, inducing another storm to form over the northern Plains. It will yank on this heat and the high humidity in the southern Plains and pull it north and northeastward, causing showers and thunderstorms to break out Thursday night into Friday that will move east-southeastward to southeast across the Midwest toward the Ohio Valley.
Where this track will be critical to temperature forecasts on Friday from the Midwest and mid-Mississippi Valley into the Ohio Valley and even parts of the Tennessee Valley, and the models are all over the place with this. Look at the 12z NAM 850mb temperature forecast for Friday evening:
That's a blast furnace of heat back in Kansas! The farther north and east it comes Friday, the higher the temperatures are going to be, plain and simple. It could easily surge past 100 across a big chunk of Missouri if the storms bypass the state to the northeast. On the other hand, if it rains in the morning, and it stays cloudy, it could stay in the 70s in Illinois and nearby areas!
This surge of heat never gets to the Northeast, and looming over the horizon is a much deeper upper-level trough, one that will renew last week's chill across the nation's heartland. Here's just a peek at what that might look like next Tuesday:
I suspect it will be even cooler than that!
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