Of all the days for a snowstorm – the day before Thanksgiving is probably the worst. Even I’m finding it tough to get excited about this storm – and I can’t even sleep at night before snow because I’m so excited about it most of the time.
For one, the lack of a cold surface high to the north will keep temperatures on the mild side in the lowest thousand or two feet of the atmosphere. Particularly vulnerable will be the shoreline where there will initially be a bit of an easterly component to the wind off the warm Sound. It’s certainly possible that the snow hole of Groton/New London is unable to get measurable snow due to temperatures a bit too warm near the ground.
A second item of concern is the track of the mid level low – particularly around 10,000 feet above the ground at 700 mb.
Here on the 18z GFS the 700 mb low closes off to our west across southeastern New York. You generally want the 700mb low overhead or just east to really cash in with the heaviest snow. While the initial thump of snow along the mid level warm front will be impressive (strong isentropic upglide) the “comma head” should stay a bit to the northwest of Connecticut – unless models bring this entire system a bit east.
A third issue is relatively crummy dendritic growth. Efficient production of snow flakes (dendrites) is maximized in temperatures near -15C. The dendritic growth zone is between -12C and -18C. In this storm the DGZ is quite high in the atmosphere (above 500mb) and there are several sneaky dry layers around. This makes me a bit bearish – I’d much prefer to see good lift/RH in the snow growth zone. This can lead to a period of ice crystals that are ineffecient accumulators (death needles and colums are the worst!!!).
Another way to view this is in a time-height profile for KHFD on BUFKIT with omega contoured along with RH and the snow growth zone. You can see the omega bullseye and best RH is under the snow growth zone. Things improve a bit from a snow growth perspective in northwestern Connecticut and especially the Berkshires.
Putting it all together there are a number of factors to make us a bit “bearish” on this one than we’d otherwise be.
The GFS is printing out nearly an inch of liquid for most of Connecticut while the European model has between 1.0″ and 1.5″ across the state. The combination of borderline boundary layer temperatures, a mid level low track that is not particularly favorable, and crummy snow growth we’re shaving quite a bit off what you’d expect from just taking a straight 10:1 snow to liquid ratio.
Obviously things can change – a cooler boundary layer, a mid level low track that’s farther east placing us in an area of better frontogenesis/mid level life, or better snow growth are all things we’ll have to look out for. Conversely, lighter snowfall rates and a warmer boundary layer could yield unimpressive snow totals. Regardless, the Wednesday travel day before Thanksgiving looks like a mess.