Arctic plunge Sunday, potential storm near Thanksgiving?

Good afternoon! After a period of moderation in temperatures over the next couple of days and perhaps a few scattered showers on Friday and Saturday, an Arctic cold front will be crossing the area sometime on Saturday. This will lead to plunging temperatures on Saturday night and Sunday.

Today's 12z European Model valid for Sunday afternoon shows 850mb temperatures in between -15C and -18C. This supports temperatures not getting above freezing. Image credit goes to weatherbell.com

Today’s 12z European Model valid for Sunday afternoon shows 850mb temperatures in between -15C and -18C. This supports temperatures not getting above freezing. Image credit goes to weatherbell.com

850mb temperatures are expected to drop to between -15C and -18C. With full sunshine, you can normally add around 15C to that temperature to get what is expected at the surface; thus supporting highs in the upper 20s to low 30s on Sunday, as seen in the image below.

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Today’s 12z European Model shows maximum temperatures not getting above freezing for most locations on Sunday afternoon. Image credit goes to weatherbell.com.

Today's 12z European Model valid for Sunday morning shows 1000-500mb thicknesses approaching 504dam. This supports temperatures not getting above freezing on Sunday. Image credit goes to weatherbell.com

Today’s 12z European Model valid for Sunday morning shows 1000-500mb thicknesses approaching 504dam. Image credit goes to weatherbell.com.

Additionally, the 1000-500mb thicknesses will be quite low as well. This supports the theme of a very cold pocket of air aloft. This cold pocket of air aloft will yield an unstable atmosphere, capable of producing very strong winds. It is possible that winds could gust between 30-50 miles per hour on Sunday, leading to wind chills potentially staying in the teens throughout portions of the day. It’ll truly feel like winter. Sunday night will be cold, with widespread lows in the upper teens and lower 20s.

Monday will be quite chilly as well, but a few degrees warmer and much less windy. Then once that main trough moves out, we get a bit of ridging and moderation on Tuesday out ahead of a potential storm system as we head towards Wednesday.

Let’s take a quick look at the setup.

Today's 12z European Model valid for Tuesday evening shows the setup for the potential storm system on Wednesday. It does not look favorable for a snowstorm at this time. Image credit goes to the WSI Model Lab.

Today’s 12z European Model valid for Tuesday evening shows the setup for the potential storm system on Wednesday. It does not look favorable for a snowstorm at this time. Image credit goes to the WSI Model Lab.

Today’s 12z European Model valid for Tuesday evening shows four key features at the 500mb (~15,000 feet high) level:

1) An abundant piece of energy with high moisture content along the Gulf Coast.

2) A reinforcing shot of cold air and potent piece of energy dropping down into the Plains and Midwest.

3) A ridge along the west coast that tends to flatten a bit with time.

4) A very fast flow in the Atlantic and SE Canada thanks to a lack of blocking.

The two pieces of energy will try to merge as piece #1 drops down the downstream side of the west coast ridge. As they merge, the pattern becomes favorable for a storm system to potentially climb up the coast. However, features #3 and #4 should prevent an east coast snowstorm.

This is because the ridge flattening and the lack of blocking will prevent the northern stream piece from truly dropping down southward enough to cleanly phase with the southern piece. Without a clean phase, the cold air will stay well west of the storm when it arrives. A partial phase will allow a storm to climb the coast, but not one with a ton of cold air. This leads to the scenario of today’s European Model which shows a soaking 2-3″ of rain with cold air well to the west.

Today's 12z European Model shows a rainstorm for the east with cold air located well to the west, as evidenced by the cold thicknesses remaining in the Great Lakes. Image credit goes to weatherbell.com

Today’s 12z European Model shows a rainstorm for the east with cold air located well to the west, as evidenced by the cold thicknesses remaining in the Great Lakes. Image credit goes to weatherbell.com.

As seen above, the Euro shows heavy rain for the area on Wednesday morning with not much cold air to be found.

Another scenario is that the lack of blocking to slow the pattern down will lead to a complete miss of the northern and southern stream, as they both fly east instead of the north piece dropping south and the south piece moving north, leading the storm to escape out to sea. This is still a viable possibility.

The scenario where the storm actually cleanly phases and draws cold air into the storm and leads to a snowstorm is not impossible, but quite unlikely.

What does appear likely is that when that northern piece of energy finally does move into the region, a strong reinforcing shot of cold air will move in for Thanksgiving, leading to a bitterly cold holiday.

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