Thursday, 11:35 a.m.
It will take not one, not two, but three separates features to carve out the deep upper-level trough in the East that will bring some very cold air into the South and East this weekend. Eventually we'll end up with one strong storm heading into Nova Scotia and New Brunswick late Sunday and Sunday night, one that will brush southern and especially eastern New England with some snow Saturday night and Sunday.
To get there we'll have to track these individual systems. Let's see if we can find them this morning. To do so, here's the morning water vapor imagery:
Now look at a 500mb chart for this afternoon:
It's pretty easy to pick out the first feature - if you include the surface weather map, which shows a storm over Lake Michigan. It has delivered several inches of snow to areas from central North Dakota into parts of Minnesota, then central and northern Wisconsin. Now it's snow with this low in parts of Michigan, too, and as the storm moves eastward, then east-northeast tonight and tomorrow into southwest Quebec, it will bring a cold front through the Midwest and Great Lakes, then across the Ohio Valley.
The second feature is a little harder to pick out, but it's coming out of the eastern Rockies and western High Plains. It'll generate some snow in Colorado this afternoon and tonight, then seemingly disappear tomorrow morning as it crosses the Plains and mid-Mississippi Valley. However, as it starts to lift a warmer air mass out ahead of it approaching the Appalachians, it will become increasingly unstable, and rain and snow showers will start to break out. This then will grow into a larger area of precipitation tomorrow night that will expand as it heads across Virginia and Maryland toward southeastern Pennsylvania, Delaware and New Jersey. While some of this will be in the form of rain, some of it will be snow, or rain changing to snow, and it could easily result in a 'surprise' few inches of snow somewhere in that area.
I use that 'surprise' term because of what I got in my backyard last evening, about 4 or 5 inches of heavy, wet snow that I never saw coming! I figured it would snow a little, but that the main area of precipitation would be farther south. Instead, as the upper-level feature tracked across the Ohio Valley then into south-central Pennsylvania, it set up a band of heavy snow that was no more than 50 miles wide north to south. However, those caught in it got a 3- to 5-hour period of snow that was probably made that much worse by elevation. Areas just north of this band got much, much less snow, and south and east of it, a lot less, too.
Anyway, that could be a real headache to forecasters tomorrow night into Saturday.
The final piece is coming into British Columbia now. It will turn southeastward tonight and streak across the Rockies and Plains tomorrow, then dive into the South tomorrow night. By late Saturday, it will be establishing the base of the upper-level trough:
As that feature then turns the corner Saturday night and heads northeastward off the East Coast, the pressures will steadily lower over the Gulf Stream. There won't be a surface high to overrun ahead of this feature, not with the two aforementioned features rolling by or through the Northeast ahead of it, but it will generate an expanding area of precipitation that may impact the eastern Carolinas, eastern Virginia and the Delmarva Peninsula, but the best chance of seeing accumulating snows would be over eastern New England later Saturday night and Sunday.
In the end, the deepening trough will mature Saturday night, with some very cold air drilling into Florida behind it. And the East will also be much colder this weekend, especially Sunday, before the trough lifts out and some warming can ensue for a short time early next week.
A snow storm affecting the central Plains and Midwest into the Great Lakes this afternoon into tomorrow night will be followed by the first of two arctic outbreaks around the country before Thanksgiving.
Winter is six weeks away, and there will be a couple of signs this week of the approaching season as a storm develops on the western Plains and heads through the Great Lakes.
A warm pattern is setting up for much of the nation next week.
Tropical moisture associated with the one-time Hurricane Patricia will bring heavy rains to many areas east of the Mississippi Valley between now and Wednesday night.
Patricia, the strongest hurricane on record in the eastern Pacific, will make landfall this evening in Mexico. It will spread torrential rains into East Texas, and impact the weather all the way to the Northeast next week.