Inching Closer to Snow this Weekend

As many of you know by now, there are two threats for snow over the next few days: the first of which starting late Thursday night and Friday, and the second of which on Saturday. While most model guidance verbatim is still not impressive with either threat, there have been many impressive trends today, particularly with the second storm, as that one has a much higher ceiling. The UKMET model, for example, shows a big snowstorm for a 2nd straight run, the ECMWF and its ensembles made another large jog westward.

The first disturbance is via a Polar shortwave that dives southward into the Northern Plains from Canada. This shortwave is pretty potent and resembles a lot of past setups that have a late-blooming low pressure that drop a few inches of fluffy, high-ratio snow. What’s preventing this event from having a truly high ceiling is that this shortwave is not truly detached from the downstream flow and initial vortex in SE Canada, so it cannot become its own entity. This shunts the positive vorticity advection main access offshore where there is a separate area of disjointed vorticity rather than the area where the main shortwave is. The main shortwave instead simply serves to buckle the flow a bit and provide more dynamics rather than directly correlate with the track of the system. That being said, this shortwave may still trend amplified enough to allow a last second north jump with a weak low pressure offshore that can give a few inches of snow to coastal areas.

The second disturbance is a strong Pacific shortwave that initially sits off of the West Coast but then partially phases into the wave that attempts to give us snow on Friday. But with the flow being so fast to the east and still slow out west, it allows a good chunk of the energy to break off from the trough and become its own entity. It then amplifies in the Southern Plains and taps into some Gulf of Mexico moisture, fueling a large increase in moisture. The question from here becomes if the pattern can become amplified enough downstream despite the initially fast flow and shunted baroclinic zone. However something that has been quite evident in the past few model cycles is the fact that there has been more PNA ridging out west, a more aggressive second northern stream Polar Vortex piece diving towards the storm in an attempt to interact, which also buckles the trough and upstream flow, as well as more of a pseudo -NAO in the Davis Straight. All of this may allow the storm to continue trending closer to the coast with time, but we are not yet confident it will come close enough for a major snowstorm.

The video below explains the threats in much more detail: