Thursday, 11:30 a.m.
Another cold front is on the move today, and it will result in rather significant changes in the weather for places that are currently much above normal and even more so those with the heat and that have high humidity as well. Low pressure tracking across the northern half of Minnesota now will cut north of Lake Superior tonight, then into northern Quebec tomorrow. As it does, a cold front will be pulled southeastward through the northern Plains this afternoon, then down into the central Plains and across the Midwest tonight. Here's the Sept. 4 12z NAM forecast for tomorrow morning:
Ahead of the cold front, it is going to be mighty warm and humid, if not hot and steamy, this afternoon. This surge of torrid air has been generating a lot of thunderstorms overnight and this morning across parts of Iowa, Wisconsin and northern Illinois into northern Indiana and Michigan. These should collapse early this afternoon, allowing the heat and humidity to surge northeastward. Meanwhile, the cold front itself will not be all that active considering the change in air mass from one side of the front to the other. Severe weather will generally not accompany this front over the next 24 to 36 hours.
Tomorrow, the heat and humidity will swelter the Ohio Valley, with some of it bleeding over into the mid-Atlantic states and even southern New England. While I'm not quite ready to commit to it being the last time it will be this warm in these areas for the rest of 2014, it will be hard to do again, especially since it will be much cooler behind the front for several days. And the pattern after that through the middle of the month just won't foster heat from the Midwest to the mid-Atlantic and New England.
The front should get to the New England and mid-Atlantic coast Saturday night. Here's the NAM surface forecast for Saturday evening:
Again, severe weather is not very likely with the front in most of New England and the mid-Atlantic states.
The cooler and much less humid air mass now blasting down the Front Range of the Rockies and across the northern Plains will have no trouble getting to the Northeast Saturday night and Sunday, but it won't get to the South. The strong west-to-east ridge extending from the southern Plains to off the Southeast coast will hold its ground. Look at the 500mb forecast for Monday evening:
This will mean temperatures near to a little above normal from Texas to Georgia and South Carolina through the early part of next week. How long will that last? Well, if the latest model projections are to be believed, even these areas are in jeopardy for turning quite a bit cooler by the middle of the month. Look at the 6z GFS ensemble forecast of temperature anomalies for next Wednesday:
Once again, another significant buckling of the jet stream appears ready to take place later next week, and that means another invasion of much cooler-than-normal air, starting first in the northern Rockies and northern Plains, then spreading much farther south and east late next week and next weekend.
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.