Thursday, 11:20 a.m.
A cold front has been moving steadily across the Midwest, then the Great Lakes and Ohio Valley, then finally through New England and the mid-Atlantic states over the past couple of days. Unlike its predecessor a week ago, this one actually managed to clear most coastal locations late yesterday or last night, and what a difference it has made! The relentless humidity of the past month in the mid-Atlantic and much of southern and eastern New England has given way to a refreshingly cool air mass with much lower humidity! Dew point temperatures than have been persistently pegging the top end of the scale at 70 or better have suddenly fallen into the 50s and lower 60s.
Here is a sampling of early morning low temperatures:
For the first time since June 23, the temperature fell below 70 in Philadelphia before midnight during Wednesday night, ending a string of 30 consecutive days of being so warm. Along the Delmarva Peninsula and at the Jersey shore, a stiff northeast wind is blowing to accentuate the 'chill,' even though morning temperatures in the 60s to near 70 degrees would not normally be considered far from average. However, when you contrast that to most mornings in the past five weeks that have been in the 70s with dew points to match, it really plays up the difference!
Where the sky did clear last night and closer to the surface high up over southwest Quebec and the Adirondacks, temperatures slipped into the 40s, easily the coolest morning since the middle of June, if not earlier. In fact, I saw Bradford slipped to 39 degrees, and other places in north central Pennsylvania slipped into the lower 40s, such as Kane (40), Oswayo (41), Coudersport (42) and Wellsboro and Philipsburg (43). The lowest I saw on the hourly observations was Saranac Lake, N.Y., at 33!
What a difference from one side of the front to the other!
And we're not done. An even chillier air mass is building over west-central Canada, one that saw overnight lows slip into the upper 30s and 40s across some of the Prairies:
The feature moving across the northern Plains this afternoon and evening and into the Midwest overnight and tomorrow morning will close off an upper-level low pressure area over the Upper Midwest, the northern Great Lakes and southwestern Ontario. The 12z July 25 NAM 500mb forecast shows just how intense this feature may get when you look at its forecast for late Saturday night:
If you look at the corresponding 850mb temperature forecasts across the eastern Plains and Midwest into the northern and western Ohio Valley and much of the Great Lakes going into the weekend and through it, you'll note that most places are being forecast to below 10C and some even cooler than 5C! If you were to mix that air down to sea level and completely dry it out, you might see readings in the high 60s to at best high 70s. Again, that's assuming full mixing and full sunshine! Quite often, with relatively high sun angles, you can get the good mixing, especially if there's sunshine. However, if there are a lot of clouds for various and sundry reasons, then you would fall shy of those levels. To put that into perspective, temperatures in much of this area normally reach 80 or slightly higher. That essentially means much of the northern Plains and Midwest will have readings more typical of September this weekend, rather than late July! Here's the forecast anomalies for Saturday:
As well as Sunday:
In other words, it will feel like anything but summer this weekend in areas behind this second cold front!
Now, if you want warmth, maybe head north, like to Alaska. Yesterday marked the 32nd day already this summer that the temperature has officially reached or exceeded 70 degrees in Anchorage, now putting it in a tie for fifth place with 1947. Next on the list is 1977 with 34 days of 70-degree warmth, followed by 2005 (42), 1936! (43) and 2004 (49). There's still a lot of time left to move up on that list, certainly into fourth place, perhaps higher.
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