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Monday, 11:59 a.m.
A strong cold front is making steady progress south and east this morning, and the air behind it is much drier and much cooler than the air ahead of it. Here's the latest surface pressure analysis from NOAA:
Let me quickly address the air mass and weather ahead of this front. Look back at the severe weather reports from 12z Sunday to 12z Monday:
It was very warm to downright hot and sticky ahead of this front yesterday, and with such a strong contrast between two very different air masses, it was no wonder that we saw so many severe weather reports! It remains very humid ahead of this front in the East and up into New England, and we've already seen some reports of severe weather in and around Boston, including a tornado in Revere earlier this morning. All of that will be pushed off the Northeast coast in short order once the front moves through. The same front and the same steamy air mass can also trigger strong to severe thunderstorms in the Gulf Coast region to the Southeast coast before the very same front can move by tonight.
Then the cooler, drier air wins out. How much drier? How about dew points slipping below 60 degrees tomorrow in the Florida Panhandle. For the second time this month! That's not the real story, though. It's the magnitude of the cool weather over such an extended period of time. Take a look at the GFS ensemble 2-meter temperature anomalies averaged over the next seven days combined:
Study that for a moment and let it sink in. We're talking departures over a seven-day period combing out to 6 to 12 degrees below normal from the Plains to the Mississippi Valley and beyond. Not just one day, but a full week. Which means some individual days are apt to be even farther below normal! Look at the departures from normal of the 500mb heights for tomorrow evening:
And it stays like this all week long. That same image for Friday evening:
This deep upper-level trough is really pinched in between two strong upper-level ridges, one fostering heat over the Northwest and up into western Canada and the other out over the Atlantic. The latter one will be far enough off the East coast to prevent any heat from returning to the Northeast and mid-Atlantic states through at least the beginning of the weekend, if not longer. Thus, the cool air, now that it is plunging deep down the Plains and Mississippi Valley, will have no escape route, and will instead hold its ground before slowly beginning to moderate over the weekend and next week.
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