Thursday, 11:50 a.m.
The first real big push of chilly air is now fully in place over the eastern half of the country. Just look at the high temperatures from Wednesday afternoon:
Early morning lows dropped to the 40s (or lower) throughout the Southeast and much of the Southeast, and there were many locations in central and northern Texas got that low as well. High pressure over the lower Mississippi Valley will foster a bright afternoon throughout the South, and underneath that high tonight, it will be every bit as chilly tonight, if not more so.
And this is just the first push of chilly air in the pattern. There are several more to come in the next week or so.
The next one will come behind a fairly vigorous upper-level disturbance approaching the Upper Midwest. Examine the 12z Oct. 24 NAM 500mb forecast for tomorrow evening:
The corresponding surface chart shows a decent low pressure area approaching Lake Superior:
If you study that map, you'll note the thermal trough associated with the first shot of chilly air is along the East Coast. High pressure over Tennessee will promote a southwest flow of milder air across the Midwest toward the western Great Lakes on the south side of that storm. By the end of the day tomorrow, though, a cold front will arc out of that storm through northern Minnesota into northern South Dakota, with a surface high right behind coming out of Alberta.
The 850mb forecast for Saturday afternoon might show this next shot of chillier air a little better:
By this time, the cooler air will be in place throughout the Dakotas and Midwest, while milder air is charging across the Mississippi Valley into the Ohio Valley on the south side of the front.
The surface storm will move mainly east Saturday night and Sunday across southern Quebec. The accompanying cold front will slip across the Northeast into the mid-Atlantic states Saturday night into Sunday, forestalling any gains in temperatures made on Saturday.
If you study that map closely, you will notice another warm advection/cold advection couplet across Saskatchewan and Alberta. That will be the NEXT feature that will bring another push of chilly air into the pattern. Look at the NAM surface forecast for Sunday evening:
That next front is already sliding into the northern Plains and northern Minnesota, and a much stronger surface high will push some very chilly air into the northern Rockies and northern Plains Sunday night and Monday. The air will be plenty cold enough to generate snow to start next week in these same areas. By the time we finish Monday, that chilly air will be moving into the Northeast and mid-Atlantic states, once again delaying the warmup that is inevitable later next week.
A bigger push of arctic air is heading into the Rockies early next week, perhaps a bit slower moving in than had been forecast earlier in the week, but it won't be denied. The trough that rolls into the Rockies will eventually come out across the Plains at midweek then head eastward over the second half of the week. That will effectively represent the fourth push of cold air in the pattern, one that won't be as strong in the East late next week and next weekend as what is currently in place, but it will be chilly, nonetheless.
Two systems will delay the onset of warm weather in the Ohio Valley and the East over the next week or so, but then it should get warm all across the country heading into the Memorial Day weekend.
A turn to much colder air over the Northeast and mid-Atlantic states will set the stage for a rain and snow storm later this weekend before it turns much warmer later next week.
It's warm now, but will turn much colder this weekend, with a storm threat later Saturday into Sunday. Warmth will return by the second half of next week.
Though it is cold now east of the Mississippi, with a couple of opportunities for snow into the weekend, a blast of warmth is due for much of the country east of the Rockies next week.
Warm air will once again surge eastward from the Plains to the East Coast this weekend and early next week. A strong storm next Tuesday and Wednesday will then be followed by colder air later next week.
A storm in Southeast Texas will generate severe thunderstorms this afternoon and tonight, and some wet snow on its western flank as it heads into the Ohio Valley tomorrow.