Winter's Finale: March 20th-21st Snowstorm

Sanchize06 wrote:Great runs overnight from the EURO,NAM, and GFS. Had a feeling 0z NAM was wrong, hopefully keeps correcting NW. Would assume to see some Winter Storm Watches with the afternoon updates, at least from Mt. Holly anyway

jmanley32 wrote:Did u all see rpm woah especially for pa and northern NJ.

Frank_Wx wrote:At this stage of the game I am fairly confident our area will be impacted by our 4th major storm of this month next week. There are unknowns - availability of cold air to the coast, timing, duration, etc - but those will be resolved over the weekend. The purpose of this post will be to examine the pieces and show why we're seeing differences run to run on the models.



I labeled 4 elements on this 500mb anomaly map valid for Monday night.

1. NAO region
2. 50/50 Low or Confluence region
3. Trough
4. EPO / PNA region

Now take a look at the run to run differences at these 4 locations between the 06z and 00z GFS



The 06z GFS shows a stronger -NAO over Greenland and a more expansive -EPO/+PNA in the western U.S. The confluence area is about the same, more consolidations on the 06z GFS, and the trough is also stronger and more consolidated on the 06z GFS compared to 00z. The biggest takeaway? Models are not done trending with these upper air features. This is the type of system where one small change in the upper atmosphere will create a new solution at the surface on the models.



Let's take a peak at what the upper energy tries to do. The fuchsia circles are key pieces of upper energy critical to the evolution of our storm system. The eastern-most circle is a closed 500mb vort that is responsible for developing a primary low pressure near Oklahoma. This low tracks almost due east, and because of strong temperature and pressure gradients across the north there is a large swath of precipitation that develops in the Midwest that tracks east towards us. Earlier this week we saw some models cut this primary low west near Ohio, but because of the blocking to the north (HP but also a press from the -EPO) models have given up on that solution for the time being. They key is not so much the surface low but the closed 500mb vort. Where does it track and how strong does it get? The 00z GFS showed a weaker 500mb vort so heights along the east coast, coupled with the confluence to the north, remained dampened which kept enough cold air in place for precip to fall in the form of snow. The 06z GFS showed a stronger vort so heights were higher which lead to rising temps and more rain/mix along the coast.

What ends up happening, in my depiction of this whole thing, is the initial 500mb vort breaks apart near the east coast once it "feels" all this blocking in the Atlantic. The 1st half of this system comes from that 500mb vort that broke off the bowling ball upper low in the eastern Pacific. Then we have all these other upper level vorts (the other 3 fuchsia color circles) that are phasing into the trough and creating a brand new 500mb closed low somewhere along the east coast. Where this "2nd" closed low develops will ultimately determine which areas see the greatest amount of snowfall. It is possible some areas see rain/mix from the 1st half of this storm, then depending on where the new 500mb vort forms, see snow the 2nd half. OR some area could stay ALL SNOW for the 1st and 2nd half of this entire event - which is modeled to be greater than 24 hours long.

It is also possible models slow everything down and all these energies consolidate to form just 1 storm. That would eliminate the 2-part storm idea and likely cut down on duration too.

Whatever the case, a very complex storm to forecast and I think someone - as far south as DC to Bawston - could see Godzilla (12"+) or even Roidzilla (24"+) snowfall amounts depending on which scenario comes to fruition. My gut feeling is telling me DC and the Mid-Atlantic is too far south to get into high snow accumulations. I think interior sections, from south-central PA to NEPA, NW NJ, into CT are in a very good spot. The coast, such as Philly to NYC, are on that line. I think these are the cities that could benefit from the "new" closed 500mb vort that develops. These cities could start as rain (from the initial closed 500mb low that raises heights too much) then change to snow later Tuesday or Wednesday. Again, nothing is set in stone but I am just spit balling some realistic scenarios given the time of year.

We'll see what happens.

Happy Tracking - ciao a tutti,

Frank

amugs wrote:

syosnow94 wrote:I’m actually hoping for a period of moderate to heavy sleet at the onset.  This will coat the ground and then give our snow aMUCH BETTER CHANCE of accumulating right from the get go.  SCI AT 100%

Jim great point - you want this to start - it will actually cool the ground/surface better and faster and give a layer that will allow the snow stick once it flips.

syosnow94 wrote:........By the way when Frank posts about wave 1 leaving excess energy offshore that helps to fuel our nor’easter it is EXACTLY what I posted late last week!  I don’t get the science or analysis right that often but when I do you can bet I’m going to point it out.

Frank_Wx wrote:

syosnow94 wrote:........By the way when Frank posts about wave 1 leaving excess energy offshore that helps to fuel our nor’easter it is EXACTLY what I posted late last week!  I don’t get the science or analysis right that often but when I do you can bet I’m going to point it out.

syosnow94 wrote:Frank or Alex....Any chance we start as sleet, or at least start before daybreak Wednesday?