Wednesday, 11:45 a.m.
It may be the latter third of July, but there's not going to be a lot of heat across the country in the waning days of the month. A strong cold front is charging across the Great Lakes and Ohio Valley at this hour, and while hot, steamy air is being squeezed into the mid-Atlantic and New England ahead of it, the tropical air mass will be short-lived. Much cooler air will move right in behind the front this afternoon and tonight throughout the Great Lakes and Ohio Valley with a dramatic lowering of the dew points, as will be the case over northern New England. That change won't be quite as dramatic in southern New England and the mid-Atlantic states tomorrow and tomorrow night, but it will cool off and turn less humid.
This initial air cool air mass is impressive in its own right, as a strong (by July standards) surface high coming out of southern Manitoba (1027mb) drives the cooler, drier air down to the Tennessee Valley and into the East. Look at the projected temperature anomalies for tomorrow:
This cool air mass will be replaced by a torrid one on Friday in the central Plains, with temperatures heading toward the century mark in Kansas and Oklahoma. That heat and humidity, as it tries to push farther downstream, will trigger some thunderstorms across the Midwest and mid-Mississippi Valley that will then head to the east and southeast Friday into Friday night. The heat will try to follow, but it will run into more and more resistance over time. Still, Saturday looks to be oppressive across Kansas, Oklahoma and Arkansas into much of Missouri, and that heat and brutal humidity appears likely on southernmost Illinois and Kentucky into Tennessee. By Sunday, some of that same heat and humidity will make it over to the mid-Atlantic states, but not into New England and upstate New York as well as the Great Lakes.
Then a much more impressive cool air mass will swoop down into the Plains and Mississippi Valley. Just like last week, with the so-called 'polar vortex' dropped into the Midwest and rolled across the Great Lakes, a similarly strong upper-level low will roll across the northern Plains into the Midwest with similar results. Look at the GFS forecast of 500mb heights and anomalies for next Tuesday afternoon:
Look familiar? It's eerily similar to what we saw just a week ago, and it will mean another round of much below-normal temperatures up and down the Plains states eastward to the Appalachians. It won't be quite as cool along the Eastern Seaboard, but it will be cooler. The core of the cool air is easily in the Mississippi Valley to the Ohio and Tennessee valleys. Look at the projected seven-day means for next week:
At this rate, we might have start thinking about the first snowflakes of the season in the not-too-distant future!
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.