Monday, 11:35 a.m.
Summer won't back down without a little bit of a fight, so it seems. The official end of the season is three weeks away, but today marks the beginning of meteorological autumn. Average temperatures have slipped several degrees from their peak about five weeks ago, and with the days rapidly growing shorter, the opportunities to have a hot, humid day are few and far between.
It got sneaky hot yesterday in parts of the mid-Atlantic states. Here are those official highs from Sunday:
I say 'sneaky,' as it really occurred in a small area south of an upper-level disturbance that generated plenty of clouds and some showers and a few thunderstorms from parts of Kentucky, Ohio and West Virginia into Pennsylvania and upstate New York. South of this area where it rained little or not at all and there was some sunshine, temperatures basically went through the roof.
There is a cold front coming through the Midwest into the central Plains. Severe thunderstorms are likely this afternoon and early tonight with and ahead of this front from southeastern Kansas and northeastern Oklahoma through southern Missouri into the Ohio Valley and lower Great Lakes. The air mass ahead of this front is very humid with dew points of 70 or better. With some sunshine and highs in the 80s to near 90, it will foment strong to locally severe thunderstorms later this afternoon and early tonight.
The strongest thunderstorms tomorrow will extend from the mid-Mississippi Valley through the Ohio Valley into western New York state. As the front presses farther east and southeast tomorrow into tomorrow night, it will lose much of its punch. So, aside from a few strong thunderstorms moving through northeastern New York state and northern New England tomorrow night, the front will come through southern New England and the mid-Atlantic states relatively quietly.
Wednesday won't be as hot or as oppressive behind this front, but the mid-Atlantic states will still be very warm and moderately humid, with temperatures still above normal. By Wednesday afternoon, the humidity and heat will once again be surging from the central Plains into the northern Plains and Midwest. As the next upstream upper-level trough crosses the Dakotas later Thursday, it will push another strong front across the Dakotas into Nebraska and the Midwest. I suspect there will be severe thunderstorms over the eastern Dakotas and Minnesota late Thursday into Thursday night ahead of the front, then on Friday across the rest of the Midwest down into the central Plains.
However, before this front comes through, look for one more surge of heat and humidity coming out of the Plains and Midwest into the Ohio Valley and lower Great Lakes. It will get quite warm to downright hot in the mid-Atlantic states into parts of New England later Thursday and especially Friday into Saturday. Here's the projected 6-hour maximum 2-meter temperatures for Friday afternoon from the 6z September GFS model:
How warm it gets Saturday in the mid-Atlantic and southern New England will depend upon the speed of the next cold front. Regardless, behind the front the heat and humidity will be wiped out for a while, as a large surface high will first build into the northern Plains, then across the Midwest and Great Lakes later Friday and Friday to bring a hint of fall into the atmosphere across these areas. It won't get cold enough for frost this time around, but it will be a reminder that those days are not far away.
A generally quiet and warm weather pattern will prevail around much of the country for the better part of the next week.
With the storm rolling away from the Southeast this afternoon and tonight, a more typical west-to-east flow pattern will take over in much of the nation heading into the middle of October.
Heavy rains are exiting the Northeast this afternoon, but more excessive rains will return to the mid-Atlantic later tomorrow and Friday. Hurricane Joaquin is lurking near the Bahamas, and may make the situation worse this weekend.
The system along the Southeast coast will spread heavy rain from parts of Georgia into Virginia heading into the weekend, while most of the rest of the country is dry and warm.
It may now be autumn, but much of the country will be warmer than average for the rest of the week and into the weekend.
Fall begins one week from today, but there's still plenty of warmth to go around the rest of this week, with more to follow again next week.