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Believe it or not, the atmosphere is already configuring itself to set up Tuesday's possible storm by late Friday. The storm we'll see tomorrow, which will drop a general 3 to 6 inches of snow, will scoot North-Northeast toward the NW Atlantic and get trapped under a blocking ridge. Better known as a -NAO. The development of a -NAO is critical. It sets up a "traffic jam" in our atmosphere and buckles the northern jet stream so that storm systems end up slowing or even halting in their tracks. Downstream, this results in amplification of various 500mb features such as upper level ridges or troughs. With the -NAO (check out the signature ridge over Greenland), we also see a +PNA (ridge over west U.S.) and -WPO (ridge over NPAC). This trio of teleconnections are the main reason why I am excited about Tuesday's possible storm.
The first image I posted was the GEFS (GFS Ensembles) valid Friday evening. This one is the EPS (ECM Ensembles) valid Monday morning. By this point, all pieces of upper energy associated with forming Tuesday's storm are well sampled. The first thing I want to point out is the amplification out in the Pacific. That is one HECK of a ridge in the NPAC and the domino effect it has on amplifying the pattern should not be overlooked. The western ridge grows to a point of connecting, or ridge bridging, with a piece of the -NAO ridge. Anytime we see positive heights of this magnitude in the west it results in an amplifying trough over the east coast. On the Atlantic side, the -NAO helped trap a PV lobe south of Greenland (some remnant energy is there from Friday's storm too which goes to show how potent this block is), and there is confluent upper energy off the coast of eastern Canada. These features act as a block. So between the Pacific and the Atlantic, we see upper level blocking at a magnitude that has not been seen in a long time. That means *drum roll* the trough over the eastern U.S. has no choice but to amplify, consolidate upper energy at its base, and eventually turn negative. The timing at which all of this happens is critical to determining the exact track of Tuesday's storm.
The Sub-Tropical Jet streak, valid 7am Monday here, will be active and a major contributor to feeding this storm system. The dual jet streak will keep a piece of upper energy, or vort max, off the coast of North Carolina and a surface low will develop. Without blocking this surface low would usually head out to sea, but because the flow is jammed up and we have a huge and sharp 500mb trough digging into the southeast CONUS, it gets captured and tugged back to the coast.
Here's a better look at that 500mb STJ energy off the coast of the Carolina's (#1). Also notice the Polar and Pacific energies (#3 and #2, respectively). As the western ridge amplifies on the back-side, these energies phase over the east coast and the mid level trough takes a neutral position to eventually going negatively tilted.
By Tuesday morning, here is your neutral tilted trough on its way negative and you have a surface low near the Delmarva. Since the upper energy associated with this set-up is very strong, and we essentially saw a triple phase with all those branches of energy, the dynamics involved here are one of the mos impressive I've ever seen. Snow rates would be prolific. At a premium for sure.
Notice how the surface low is not very strong once it gets tugged back to the Delmarva. There is another surface low on the west side of the trough that develops which signals to me models are struggling with how to handle the upper energy. To the north, there are blocking High's which means this is likely to be a long duration event IF it comes to fruition. Probably a 24+ hour snowfall. The storm has nowhere to go!
500mb closes off Wednesday morning. Scary thing is, or I guess cool depending on your perspective, is the area still receives 1-2 FEET of snow even with an open trough. It goes to show the potential of this thing. If 500mb were to close off Tuesday morning instead, it could result in widespread 2-3 foot snowfall totals. Then again, it could also force a storm track further west, meaning a warmer solution, so for those along I-95 we may not want H5 to close off too soon.
I am placing odds of a 6"+ snowfall (Mothrazilla) at 75%. Godzilla 40% (12"+), Roidzilla 20% (24"+), Frankzilla 5% (36"+). I am not comfortable jumping fully onboard of something historic until models resolve how they handle the phasing between the 500mb energies I discussed. Just understand the atmosphere is set up in a way that lessens the risk of a storm NOT happening. So odds of something big are the best they've been all season.
I will continue bringing updates through the weekend on the forum.