Winter Storm Threats To Return After Short-Lived Warmth

Once we get through this warm-up period this weekend and early next week, our attention will turn to a pair of upper level trough's that will drop into the eastern U.S. beginning around the 15th of January. Just like our most recent winter storm after the New Year, we have to watch the energy associated within these trough's to see if they spawn a surface low pressure system that could potentially bring widespread snowfall to the area. There are a few things we should monitor these next few days:

1. How strong will the short wave energy be?
2. How much energy gets drawn into the backside of the trough?
3. How does the trough orient itself?
4. Will there be a phase?
5. Will the STJ play a role?

There are many other questions that could be asked but there is simply no way of answering these questions this early in the game. The best we can do at this point is analyze the upper level maps from the models and see if they make sense relative to the pattern. With the last storm, the surface low ended up being further west than where the models intended it to be, and that was due to the poor handling of the trough and the energy associated with it.

There are two threats I want to broadly discuss. The dates for these potential storm threats are between January 15th - 19th. As you can see from the EURO 500 mb maps above (top image is threat #1 around January 15th, bottom image is threat #2 around January 19th), there will be a pair of trough's that drop into the eastern U.S. late next week. There is some weak / transient blocking (-NAO) showing up with ridging in the western U.S. The cold air coming down with these trough's is not as impressive as the cold air we saw with the January 3rd snowstorm, but it's definitely cold enough to support snow. 

The next 4 images are the vorticity maps (EURO top / GFS bottom) that are associated with both storm threats I highlighted above. As you can see, there is an impressive amount of s/w energy embedded within these trough's, enough to certainly get our attention. In conjunction with the +PNA spike in the west and the possible -NAO signal, this could lead to an opportunity to watch for a possible snowstorm within this time frame. 

What's impressive to me is the ridging the models are advertising is pretty amplified and this is what will allow the s/w energies ejecting out of western Canada to dig into the trough. The further south they dig, the more amplification the trough will get and the better our odds are of popping a surface low near the coast. 

The signals are there for a possible east coast snowstorm to appear on the models within the coming days. The +PNA/-NAO (albeit transient) combination should at least make things interesting next week. 

Things will become much clearer once we get closer to the dates of interest and the models get better sampling of the upper level anomalies present on the playing field. Timing will also play a role. The lower heights near the Aleutians and over Alaska indicate that "kicker" type of short waves could eject out of that region and force the ridge to roll eastward sooner then expected. This would shift the favorable trough axis offshore and likely prevent storm development as the energy runs out to sea.

We'll see how things plays out! 

Francesco Paparatto