I've got to say - I'm really, really, really impressed with how this storm is shaping up. It's looking more and more likely that we're going to see a band of epic snow rates for a period tomorrow morning and midday. I eschew weather hyperbole but this one looks like the real deal.
This storm will be a bit different than many of our "big ones" due to its speed. We're only looking at a 4-6 hour window of really heavy snow. If this storm was moving anyslower we'd be talking about over 2 feet of snow - but it's trucking pretty fast to the east. With that in mind there will be some limit as to just how much snow we can get. The storms speed - and intensity - introduces another problem into the equation and that's the fact we're going to see exceptional snowfall rates at the storm's peak - possibly up to 4" per hour. That is enough to basically immobilize the state for a period of time. This storm will be very bad at its peak.
The biggest reason we're expecting these heavy snowfall rates is a band of very strong convergence will set up about 10,000 feet up. This a classic signature for heavy snow with powerful winds slowing to a crawl overhead - essentially forcing air parcels to pile up and rise. The acceleration of air in an upward direction is how we get clouds and precipitation - and in this case snow.
As I mentioned yesterday one of the things we're watching closely is the fact this strong "lift" or vertical motion is occuring where the temperature is around -15C up way above our heads in the clouds. That is the temperature at which snow flake growth is the most efficient AND the favored crystal type is a dendrite which allows snow to become fluffy and pile up quickly. A 15:1 ratio of snow to liquid is possible where this lift is maximized near -15C in the atmosphere.
I'm pretty confident there's going to be an area that gets more than 14" - maybe as much as 18". Again, the upward bound here is somewhat limited in that we're only going to have a short window of exceptionally heavy snow - it's a quick mover! Could there be more? Sure but let's not get too carried away just yet and also remember this heavy band will be very narrow geographically.
Where this heavy band sets us things are going to rip but it's important to note when these bands develop there tends to be bands of downward/sinking motion on either side of them. While some people get crushed other areas can miss out a bit. The haves and the have nots in a snowstorm (if my neighborhood is in a "have not" band I'll be livid and a supremely unpleasant person to be around tomorrow afternoon). Still, I think even with these "sucker holes" 8 inches of snow is a reasonable lower bound for most locations.
Here's the bottom line:
- Snow develops across the state 5 a.m. to 8 a.m.
- Heaviest snow between 8 a.m. and 2 p.m.
- Snow gradually winds down 2 p.m. to 6 p.m.
- 8"-14" will cover it in most areas - but a narrow band of higher snowfall totals is very possible. It's also conceivable that this heavy band sets up right along the I-84 corridor.
- Snowfall rates of 1"-4" per hour in some spots will make driving exceptionally difficult. This will be an extremely high impact storm given how quickly the snow will fall.
- Thundersnow is likely at the storm's peak.
- Winds could gust to 40 m.p.h. in southeastern Connecticut but we are not expecting widespread wind issues or any coastal flooding.
- The truly heavy snow with winds up setting up in one corner of Connecticut (say northwest or southeast) leaving the large population centers in one of those subsidence zones. A possibility - but not likely.
- Storm trends weaker and the forcing doesn't verify as currently modeled. We'd still get the low end of amounts but the really exceptional snow rates never materialize and some of my adjectives wind up overdone.
- Best lift winds up above or below the -15C level and snow ratios are much closer to 10:1 than 12:1 or 15:1 as we're currently thinking.