Much of the central and eastern United States have seen a reprieve from frigid temperatures over the last 10 days, however that will soon change as a large “blocking ridge” in the jet stream develops over Alaska and allows the Arctic floodgates to open into the continental United States later this week, sending cold weather into much of the country:

The forecast weather pattern later in the week is quite impressive, with the warm colors over the northern Pacific indicating that the jet stream is well north of where it normally is in that region, thanks to the very strong ridge over the Aleutian Islands.  On the backside of this ridge, air will come pouring in from near the North Pole into the Rockies and Midwest, with the cold quickly spilling east into the eastern United States by Wednesday and Thursday.

By Saturday evening, almost all of the country is expected to be experiencing temperatures 10 to 20 degrees normal, with locally more significant departures, particularly across the northern Rockies.  This cold weather pattern will not be without risk for some wintry weather across the central and eastern United States, however the amount of snow that ultimately falls, and where, is in question:

A look at a set of “ensembles,” or a forecast model ran 21 different times with slightly different perturbations in an attempt to establish forecast uncertainty, shows a few different hot spots for snow to watch out for over the next week.  The first little corridor to watch out for will be from the central Plains east across the Mid-Mississippi Valley into the Ohio Valley and Mid Atlantic from Wednesday night through Friday:

This will just be a little ripple in the jet stream tracking from west to east, and not a ton of snow is expected.  A few locations in this corridor may pick up a couple of inches of snow, particularly in the higher terrain and also perhaps right along the coast around the Delmarva or New Jersey as the wave becomes better developed once it gets over the warm waters of the Gulf Stream.  This wave, if it develops, could also graze far southeastern New England with some snow.  In addition to this corridor of light snow, some lake effect snow will be ongoing downwind of all of the Great Lakes by Wednesday and Thursday.

The other potential corridor of snow comes over the weekend across parts of the Southeast and Mid Atlantic, with a few ensemble members coming in with hefty snow totals in that corridor:

This potential wintry precipitation involves multiple fast moving pieces of “energy” in the jet stream (shortwave troughs is the meteorologically correct term), making it hard to pin down in advance what will happen.  Essentially, we have a piece of energy riding across the Deep South; this energy brings with it plenty of moisture.  We have another piece of energy diving into the Great Lakes from the north, bringing with it a lot of cold.  If these two pieces of energy were to combine or “phase,” a big storm would likely develop near the East Coast, possibly resulting in heavy snow on land.  Some of our models show this bigger storm coming to fruition, some do not.

Looking at the larger scale weather pattern can give us some clues as to what the likelihood of a given solution is.  The weather pattern for Friday and Saturday, as currently depicted by our models, has two big red flags if you want a significant East Coast snowstorm:

  • There is no ridge in the western US; a big ridge in this location would make it easier for our northern energy to dive south and combine with or phase with our southern energy. A big ridge in the west is known as a +PNA, and a +PNA pattern is more favorable for big East Coast snows than a –PNA pattern, which is what we will be in this Friday and Saturday.
  • There is no blocking ridge in the jet stream over the North Atlantic (commonly called a –NAO). Because of this, the jet stream moves quickly away from the Northeast, which can be inferred by the lines on this map being extremely tightly packed from off the East Coast up to Greenland. A blocking ridge in this area would also aid in slowing down both pieces of energy and giving them a chance to “phase.”

Because the weather pattern is pretty “fast moving” this Friday and Saturday, I’m skeptical that we can pull off a huge snowstorm/ice storm in places like the Carolinas and Virginia, despite what some of our models are saying.  However, with plenty of cold in place ahead of the storm, and a good shot of moisture with the southern energy regardless, a light to moderate winter weather event could still play out from parts of the southern Plains east through Arkansas into northern Mississippi, Alabama and Georgia into the Carolinas and southern and eastern Virginia.  We’ll continue to monitor this potential over the next few days for changes in the weather pattern that may allow for a more significant event…but for now it looks like a weaker event that stays a bit farther south is more likely than a huge event that rides all the way up the East Coast.

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