Active Pattern Sets Up Two Chances For Snow Along The East Coast This Week

Hello everyone!

Winter is here and there is plenty of interesting stuff to talk about from a synoptic meteorology perspective. This post will take a more in-depth look at the first of two storms expected to bring at least some snow to parts of the East Coast this week.

Here’s a glimpse at what I’m seeing on satellite imagery this morning. We have a storm moving through Illinois bringing snow to parts of the Great Lakes and rain to parts of the Northeast. While not directly bringing any wintry weather along the East Coast outside far northern Maine, this system will help set the stage for the next two systems, waiting in the wings over Oregon and Alberta. It will help chip away at the subtropical ridge over the western Atlantic, and it will shove the polar front towards the coast.

This sets up the possibility of cyclogenesis (the formation of a new storm) in the Southeast tomorrow evening as the Oregon disturbance meets up with the lower-level front.

By tomorrow evening, a classic cyclogenesis event will be underway as the upper-level disturbance from Oregon supports the development of a surface wave along the polar front.

North of this surface low, a jet streak (region of extra-fast winds embedded within the larger jet stream) is noted over the Ohio Valley. The jet streak doesn’t move forward as fast as the winds within it, so there are regions near the entrance and exit of the jet where winds aloft are accelerating and decelerating. The acceleration into the jet entrance region, particularly the right entrance region in situations like this, draws near-surface air north and upward into the jet. This circulation will contribute to the northward movement (advection) of moisture from the Gulf of Mexico and the subsequent condensation of much of that moisture into rain/snow north of the low’s track.

The critical question is how this developing storm interacts with the Alberta disturbance as it dives east-southeast towards New England.

Current forecasts show the Oregon disturbance east of the Alberta disturbance on Monday evening as it approaches the East Coast, but not by much. Perhaps more critically, the Alberta disturbance is sliding ESE rather than digging SE. That means that the prevailing flow responsible for steering the Oregon disturbance (and our storm) is more west-southwesterly than southwesterly. The result is a track towards the ENE rather than NE. So this won’t turn into a blockbuster blizzard until it gets up to Newfoundland. That doesn’t mean we don’t still have some unanswered questions about just how far northwest precipitation might be able to reach.

This loop shows the last four forecasts from the NAM model for precipitation and sea level pressure all valid Monday evening. Note that the original forecasts showed low pressure slipping offshore without much if any precipitation over the Northeast. The latest forecast has a solid moderate snow event for much of the coastal Northeast as the low tracks a bit closer to the coast.

A look at upper-level wind forecasts shows a favorable setup for northward moisture advection into the right entrance region of a jet streak that curves right as you move east along its axis (meteorologists call this “anticyclonically curved”).

If only that Alberta disturbance were digging southeast, we could have a nice blizzard on our hands but instead all our relevant features will slide quickly ENE and so too will the precipitation shield. This should produce a solid light-moderate snow event for a swath of Southern New England and adjacent parts of PA/MD.

Here’s a first guess on possible accumulations from this system.

I’m a little more bullish on this system because it’s a setup that often supports a bit of last-minute NW trending (like we saw in the NAM forecast comparison above) thanks to poorly-resolved convective processes off the East Coast. That said, I think I’d probably bet on the lower ends of these ranges at least to start.

The storm quickly departs Tuesday morning leaving very cold air poised to surge into the region.

This is true Arctic air, at least for those of us in Northern New England. This bitter cold airmass will help support heavy snow as our next system approaches on Wednesday.

More on that one later this afternoon.

Jack