It turns out that today was going to be a bit more active than I thought it would be yesterday. The Storm Prediction Center has added a huge part of the Mid-Atlantic and Southeast under a slight risk for severe weather, and they've also extended the slight risk area over the western Great Lakes to include parts of Iowa, Wisconsin, Illinois, Lake Michigan, and Michigan.
|SPC's severe weather outlook for Tuesday, issued Tuesday morning.|
A "soupy" airmass (as the NWS in Roanoke put it) is in place across much of the Southeast and Mid-Atlantic this afternoon, which will continue to grow as daytime heating takes hold and moisture continues to advect (move) northward from the Atlantic. The latest surface observation from the SPC shows a tongue of moisture extending northward into southern Pennsylvania, with uncomfortable dewpoints of 60-70+ degrees across the whole area from the Blue Ridge to the coast. Air temperatures range from the mid 60s near the mountains to the 80s near the NC/SC coastal border region.
|Surface observations from the SPC's mesoanalysis, from 16z (noon eastern).|
|Visible satellite image from 12:45 PM Eastern.|
|RAP Model forecast SB CAPE for 21z (5PM Eastern).|
Iowa to Michigan:
The RAP model shows a fairly weak cold front draped parts of the Upper Midwest extending from Lake Michigan down through southeastern WI into central Iowa later this afternoon. Temperatures in parts of Iowa and Illinois are expected to climb up into the upper 80s and lower 90s as the day progresses, setting the stage for some instability out ahead of the front. As the boundary approaches, it'll provide a focus for storms to develop despite the low dewpoints (40s and 50s). The SPC states that the storms will quickly dissipate once the sun sets and the instability fueling the storms quickly erodes. There is a general risk for damaging winds and large hail in the strongest storms that are able to form.
|RAP model forecast temps/dewpoints/pressures for 21z (4PM Central). The cold front is located in the sharp curving of the isobars from Lake Michigan through Iowa.|