Friday, 11:30 a.m.
I don't think we're quite to the point where some furnaces will be clicking on in the days ahead, but we're going to be awfully close. If we were beyond Labor Day, it would be one thing. You more or less kind of expect a shot of cool air to come in and sweep clean the air masses, and have us looking into the drawers for the long-sleeved shirts, the sweaters and the sweatshirts! But in early August? That's a bit of a stretch! Yet that's all possible in the coming week or two as we see a couple of really cool air masses for so early in the season become unleashed on the northern Plains and Midwest initially. These cool blasts will then flow on to the south and east over time and could lead to some record lows in the coming days.
The air mass that has moved into the mid-Atlantic and western New England today is not terribly cool. It may mean afternoon highs are near normal, in fact, or just a tick below average, but no more. Farther north and west, though, they are a bit farther below the norm for early August. Look at a sampling of early morning minimums in the northern Plains and up into south-central Canada:
The chilly air north of the border will advance into the Midwest tonight in the wake of an upper-level feature that will trigger some showers and thunderstorms from Illinois into the Ohio Valley this afternoon into tonight. That will set the stage for a pretty cool day tomorrow compared to normal from the Great Lakes and northern Ohio Valley on West, as depicted by the GFS ensembles for tomorrow:
As this whole trough slides across the Great Lakes to the Northeast this weekend, some of that cool air will definitely come along for the ride. The 12z Friday, Aug. 2, NAM 850mb temperature forecast for Sunday afternoon is not exactly summer like anywhere from the Midwest to the mid-Atlantic!
And that's just the first chilly air mass in this pattern! There's another one waiting in the wings that may be even chillier for the northern Plains and Midwest later next week. An upper-level low Monday evening over northern Manitoba and along the western shores of Hudson Bay will be slowly dropping southward as the week progresses:
As it does, look for a cool air mass to grow in stature next week, pushing temperatures just as far below average from the Dakotas to Michigan as they will be this weekend, perhaps even more. That particular air mass may not fully reach the East late next week and next weekend, but it's unlikely to be hot there, either.
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