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!
Warmth will expand from the Gulf Coast into the Ohio Valley and mid-Atlantic states by Memorial Day, but the wet and stormy weather will persist in the Plains, and expand across the Mississippi Valley.
Chilly, wet weather will morph into a warm, humid pattern later this weekend into next week, one that will remain unsettled, especially in the Plains and Mississippi Valley.
Severe thunderstorms will erupt over West Texas late tonight and tonight, but they'll become more widespread over a larger percentage of the Plains states later tomorrow and Saturday.
After a brief cool spell, much of the country from the Plains on east will turn warmer Friday through Sunday, but there will also be more clouds, showers and thunderstorms around as well.