In this winter even a light snow event is enough to garner some extra attention! The setup that we have is actually quite close to developing a fairly sizable snowstorm but the pieces will not come together just right this time.
Here’s the GFS 500mb height/vorticity forcast for 1 p.m. Saturday.
I circled a “vort max” or “shortwave” off the east coast. Think of this as a piece of energy in the mid levels of the atmosphere. To the west there is a large and relatively impressive trough digging through the Great Lakes. These 2 features will remain separate. They will not phase into one. That means we’re left with a relatively large but diffuse area of lift in the atmosphere offshore as opposed to a concentrated area of strong lift – which is how we get our biggest storms.
You can see the impact of that by looking at the sea level pressure prog for the same time.
Notice how diffuse the low is (i.e. not tightly packed/wound up)? This shows that this storm is going to have trouble getting organized until it reaches or passes our latitude. Not good for a big storm.
That said there will be enough lift and convergence to produce a widespread swath of snow across southern New England. Many locations will see 1″-3″ of snow. It’s possible that if the storm winds up organizing faster and closer to the coast we could see more impressive snow as a comma head develops.
There is one other thing to watch out for but at this point seems unlikely. The 00z and 06z NAM is developing an inverted trough from the low offshore back to New York City and southern Connecticut. This essentially maximizes low level convergence and
produces a narrow, but intense, band of heavy snow. At this point the NAM is the only model showing this so it’s hard to get too excited about it but it’s something to watch. The 2 panels on the left show the 06z NAM at 1 p.m. Saturday with a relative QPF max over eastern Long Island and southern Connecticut with the lower panel showing why – a band of convergence stretching north from the Atlantic toward Connecticut.
For what it’s worth the 03Z SREF guidance shows relatively robust probabilities for >4″ of snow across parts of southern New England. The blue shading is >25% chance while the green is >50% chance. At this point I think these numbers are a bit high but there is a chance that this storm trends a bit more impressive for some of the reasons discussed above.