The start of fall has come with an active weather pattern, following a relatively quiet summer. We’ve dealt with a few coastal systems, and now a strong cold front will approach from the west to begin the weekend. Starting in the southern Plains Thursday, the parent low pressure system will track toward the western Great Lakes region and strengthen Friday. A line of widespread rainfall and some t-storms will develop from the Great Lakes into the southeastern United States as it presses eastward toward the Mid-Atlantic and Northeast.
On Friday, winds will shift south ahead of the front, with areas along the Eastern Seaboard seeing temperatures near to slightly above-average (as long as cloud cover doesn’t affect heating too much). Friday Night into Saturday, this cold front will blast through the Northeast. Impacts will not be too significant, but rainfall will be widespread from the Northeast to the Gulf Coast. Rainfall totals look to generally be between 0.25” and 0.50” across much of the East Coast, with some areas seeing up to 1.00”. Behind the front, temperatures on Sunday will be much cooler, especially for overnight lows. Despite winds being a bit too strong to be ideal for cooling at night, non-coastal areas will still drop into the 40s Saturday night with even a few 30s Sunday night, as you can see in the image of MOS data below.
The most interesting part of the frontal passage, will be the cold air rushing over the Great Lakes. Current guidance suggests that the notorious ‘540 line’ will overtake portions of western New York and Pennsylvania, which is indicated by black arrows and a light blue, dashed line in the image below from GFS model valid Sunday at 8 AM. This is significant because the line can be loosely used as the boundary between rain and snow. So, with a northwest flow Saturday night into Sunday, we can’t rule out the possibility of a few snowflakes mixing in for areas bordering the Great Lakes in upstate NY and PA, circled below.
