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Greenland Block Pattern to Bring Cold and Snow to Parts of the Midwest and East Next Weekend and Into Thanksgiving Week
Published: November 12, 2017
A blocking pattern in the jet stream could bring another round of cold air, rain and snow to the Midwest and East by late in the week ahead, potentially continuing into Thanksgiving week.
(MORE: Winter Storm Central)
This pattern consists of relatively high pressure aloft strengthening and persisting near Greenland, forcing the polar jet stream to take a sharp, southward nosedive over the eastern U.S.
Meteorologists call this weather pattern a Greenland block, and it's associated with the negative phase of the North Atlantic Oscillation (negative NAO), which you can read more about at the link below.
While the pattern is of relatively high confidence, there are some impacts we're more confident about and others that remain uncertain this far out in time.
Here's an overview of what millions of Thanksgiving travelers can expect starting the weekend before the holiday.
Next Weekend: Cold Plunge Follows Midwest, Eastern Storm (High Confidence)
Sometimes, the transition to a new weather pattern is accompanied by a significant storm.
In the days before Thanksgiving last November, Winter Storm Argos spread snow and wind from the West to the Midwest before stalling over eastern Canada, hammering parts of New York state with over 2 feet of snow whipped by winds gusting over 50 mph.
That stall over eastern Canada was made possible by a transition to a negative NAO, or Greenland block pattern.
In this case, the sharp jet stream plunge may induce a low-pressure system to strengthen quickly over the Great Lakes and eastern Canada by next weekend, producing wind-whipped snow in the colder air and heavy rain in the warmer air ahead of the front. There is even a chance of severe thunderstorms on the warm side of this weather system.
Outlook: Saturday, Nov. 18
While all the details on where, when and how much snow aren't yet crystal clear, a swath from the upper Midwest to the Great Lakes snowbelts may see heavy snow, and snow is also possible in parts of northern New England from this system Friday into next weekend.
Possible Travel Delays
- Friday (Nov. 17): Snow, or rain changing to snow, along with gusty winds, may affect parts of the upper Midwest and western Great Lakes regions. Showers and thunderstorms should spread through the southern Great Lakes, Ohio Valley and South.
- Saturday (Nov. 18): Gusty winds and snow, or rain changing to snow, may impact portions of the Great Lakes and interior Northeast. Rain may spread through the Interstate 95 corridor of the Northeast and the South.
- Sunday (Nov. 19): Lake-effect snow may develop throughout the Great Lakes snowbelts.
(MAPS: 7-Day U.S. Rain/Snow Forecasts)
One near certainty in this pattern is another plunge of colder air deep into the Midwest and East by the weekend before Thanksgiving.
While the magnitude of the cold air remains uncertain this far out, this sharp of a jet stream plunge will drop temperatures below average next weekend throughout the Midwest and into the eastern states.
Forecast Highs Compared to Average Next Weekend
(MAPS: 10-Day U.S. Forecast Highs/Lows)
Thanksgiving Week: More Cold and Snow to Come?
There are indications this eastern cold may persist deep into Thanksgiving week, as blocking patterns are prone to cause.
The latest 8- to 14-day temperature outlook from NOAA's Climate Prediction Center currently favors an increased probability of below-average temperatures Thanksgiving week in the eastern states (Nov. 20-26).
Furthermore, if this pattern holds, we can't rule out an additional snowmaker, or several, rolling through the Midwest and Northeast Thanksgiving week.
For now, this is just something to keep in the back of your mind. Additional information on how this weather pattern may affect your travel plans for Thanksgiving will be available later this week.
Jonathan Erdman is a senior meteorologist at weather.com and has been an incurable weather geek since a tornado narrowly missed his childhood home in Wisconsin at age 7. Follow him on Facebook and Twitter.
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