Friday, 11:55 A.M.
With a week to go in July, we normally aren't ready to think about fall, as we're in the dog days of summer at this point, the core of the season's heat. Oh, there will be plenty of summery heat and humidity this weekend from the central Plains into the Tennessee and parts of the Ohio Valley, as well as in parts of the mid-Atlantic, but it's a temporary blast furnace of heat. What's coming next week is another hint of the season to come - autumn.
A little piece of that kind of cool air moved out of the Lakes and Midwest into the interior mid-Atlantic and New England yesterday and last night. Temperatures slipped to 39 F this morning in both Kane and Bradford, Pennsylvania, and to 41 F in Saranac Lake, New York. When I was out riding late yesterday and last evening, it was barely above 70 F with some flat cumulus clouds and a steady north wind that made it look and feel as if it was late September.
Don't look now, but that same sort of air mass is about to be unleashed on the northern Rockies and northern Plains this weekend. And it won't stop there. It will be a game changer all the way to the Deep South and the East Coast by Tuesday. The reason for it is yet another major buckling of the jet stream, in keeping with the highly amplified pattern we've been in of late. Compare the jet stream of today to that of Monday evening:
Note how the upper-level ridge over Colorado and New Mexico out into the southern Plains becomes reoriented back into the central and southern Plains, while a deeper upper-level trough is carved out over the East. It won't necessarily be a reincarnation of the "polar vortex," but the impact will be much the same as we saw just a short time ago. This will drive another cold front to the Gulf Coast, and that means a continuation of the cooler-than-normal July throughout the South.
How cool? How far below normal? Here's two snapshots - one for Tuesday, then for next Saturday:
What does that mean in terms of actual temperatures? It probably means nighttime lows dipping into the 50s into the northern part of the Gulf Coast states, or at least the Tennessee Valley. And there could be two or even three days from the Midwest to the Great Lakes and Ohio Valley with daytime highs only in the 70s. There can even be a couple of days around the Great Lakes where the afternoon highs fail to reach 70 F because of clouds and spotty showers - very much like one would see in the last days of September and the beginning days of October!
Blocking over the Atlantic and in Europe is buckling the jet stream over the central and eastern U.S. to extend the cool and wet weather the rest of the week and into the weekend.
More excessive wetness is in store from the mid-Mississippi Valley to the mid-Atlantic states, while the brutal heat continues in the West and especially the Northwest this week.
A cool season storm will bring flooding rains and very cool air to the Ohio Valley and Northeast tomorrow into the weekend, while the Northwest has record-setting heat with sunshine.
As the jet stream undergoes amplification late this week into the weekend, it will lead to extremes of heat in the Northwest and cool and wet weather in the Ohio Valley, mid-Atlantic and parts of New England.
Heat and humidity surging across the Mississippi Valley will spark severe thunderstorms in the next 24 hours. The pattern will remain wet from the northern Plains to the East Coast for a while.