Tuesday, 11:30 a.m.
A strong but relatively flat upper-level ridge is building along the West Coast these days, and it will promote escalating heat in much of the West much of the rest of the week. Examine the 0z 4 June GFS ensemble 500mb heights and anomalies for Friday evening:
Temperatures will jump into the 80s and lower 90s through the interior Northwest, with much of interior California surging past 100 for several days. Look at the projected temperature anomalies for Friday:
While the West sizzles, the Plains will chill out in the coming days. It's more or less the story of what goes up must come down. In other words, with the ridging over the West, there has to be an upper-level trough downstream, and it looks as if that trough will unravel across the Plains in the coming days. Right now it's more of an upper-level low over the Dakotas:
It's already keeping it cool from the Upper Midwest back across North Dakota to the northern Rockies, and that cool air will spread down the Front Range of the Rockies and into the central Plains over the next 24 hours. As you can see from the first image above, it is likely to lead to some double-digit departures on the negative side through Friday. It may still be that far below normal, or at least 5 to 10 below average, over much of the Plains and the middle and upper Mississippi Valley, right into Saturday!
As the upper-level trough slowly opens up, but overall deepens coming east, it will generate a fair amount of rain from the northern Plains and Midwest, particularly from parts of North Dakota and Minnesota into Wisconsin. There will also be quite a bit of shower and thunderstorm activity farther south across Kansas and Oklahoma across the Mississippi Valley into the Tennessee Valley, with some locations picking up 1-2 inches between now and the end of the day Friday.
The main concern of rain, though, is along and east of the Appalachians thanks to the disorganized area of low pressure in the south-central Gulf of Mexico. I say disorganized, as the showers and thunderstorms are well removed from the low-level center of circulation to its east and southeast thanks to a fair degree of upper-level shearing. That shearing may relax enough over the next 24 to 48 hours to allow some of the thunderstorms to start getting closer to, or remain near, that center.
In all probability, this will become a tropical depression. It's unlikely to become a hurricane before reaching Florida, but tropical storm conditions could well develop for a time. The main impact appears to be rain, and plenty of it, with some places in Florida perhaps in line for 5 to 10 inches of rain through Friday. That rain will slowly expand northeastward in coordination with the storm's movement Thursday and Friday, likely bringing excessive rains into the Southeast and up along and east of the Appalachians. To give you an idea of its potential, here's the 12z 4 June NAM model projection of precipitation from today through Friday:
That may not work out as projected, but it does suggest that after a couple of nice days in the East today and tomorrow, the rain gear will get a workout Thursday and especially Friday, if not into the start of the weekend.
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