The Skiing Weatherman February 10, 2023

In spite of last weekend’s dramatic cold outbreak over the Northeast, one that was muted at resorts further south in the mid-Atlantic states, milder than normal temperatures continue to dominate the pattern.  Not to the extent that they did in a very mild January, but enough to make every disturbance, big or small, that comes along a real nail biter in terms of rain vs. snow.  For the most part, natural snow has been confined to areas north of Interstate 90 in New York and New England, although the Catskills have cashed in a few times here in there before seeing mild air turn the precip over to something other than flakes.  There is no short-term change in sight, but all is not lost.  An infrequent event at the top of the atmosphere over the high (polar) latitudes is underway, and I believe that this phenomenon may well provide the Northeast with its most consistent snow conditions of this season from late this month through at least a good portion of March.

What’s going on high above the arctic regions is known as a Sudden Stratospheric Warming, or SSW.  At the top 1 to 3 per cent of the atmosphere, at roughly 30 miles above the surface, the air is warming rapidly, and as pressure levels grow aloft, the effect is gradually pressing down on the polar vortex that is swirling around closer to the surface at a level known as the troposphere.  Here is a graphic that illustrates the potential “before and after” of the process…

You can see the tight, symmetrical circulation over the North Pole, which is essentially what the vortex looks like right now.  The squiggly darkest blue line is what the vortex will look if the warming fully matures, spreads to the lower levels and breaks it up.  As the warming continues to descend, the vortex is attacked by the warmth at the top of the atmosphere.  Here is a graphic showing the attack at the top for the 17^th…

A strong bubble of warmth has pushed and distorted the vortex to the east…off its polar perch.  This next map shows the stratospheric temperatures the next day at well above normal levels…

As the process continues, the smooth and nearly circular flow of the vortex will get disrupted, so instead of having most of the cold air in the northern hemisphere bottled up near the North Pole, some of that air will get redistributed to the lower latitudes.  One of the key indicators if the warming and vortex disruption is enough to bring the Northeast a spell of consistently cold and snowy weather will be a change in direction of the flow around the pole.  Modeling does indeed forecast that change, and if it does occur, studies of prior SSWs tell us that although the main thrust of the coldest air will move into Siberia, an upper-level trough will form over eastern North America for an extended stay.  In that position, the trough will be poised to receive several shots of cold air from Siberia via a track up and over the Pole.  Here is a look at where the jet stream set up is headed toward the end of this month and beyond…

The most recent February SSW event of consequence was in 2018, and it is worth looking at the temperature anomalies at the surface that occurred in March and April of that year…

Typically, the cold effects of an SSW event last several weeks, and when combined with a dying La Nina, even longer.

An SSW is a very complex event and I hope I have been able to adequately describe it in the space available.  With another week of marginal temps about to unfold in the Northeast and the specter of yet another messy “cutter” storm moving up to the west of the region late next week, I chose to discuss the SSW today because I believe that there will be outstanding conditions to enjoy before this season is over.  The SSW that is underway is the meteorological mechanism that will get us there.