Saturday Snowstorm

If you don’t want to geek out and read all this… the bottom line is I expect most of us to 4″-6″ of snow in Connecticut and most of southern New England.

Finally some real snow in the forecast! Here’s the 12z NAM valid at 15z (10 a.m.) Saturday with 850mb temperatures (0c solid black) and 3-hour QPF shaded. As usual the NAM is the most robust of all our models in terms of precipitation.

A weak disturbance is ejecting east toward southern New England. Though the shortwave isn’t strong we’ll get a burst of QG forcing (lift) thanks to warm advection and a 60+ m/s jet streak to our north leaving us in the favorable right entrance region.

NAM dynamic tropopause forecast for 15z Saturday. Isotachs shown - note the 60m/s jet streak northeast of Connecticut on the DT.

12z NAM forecast of sea level pressure and 1000-500mb thickness valid 18z Saturday

In the NAM SLP/Thickness map you can see the relatively tight thickness gradient over NY and New England which will help maximize low level warm advection even with a relatively weak low level jet. In addition synoptic scale lift will be present through the column in right entrance region of jet streak to the north.

The bottom line is that snow will overspread the state shortly before daybreak Saturday with 4″-6″ of snow likely across all of Connecticut. I expect snow even down to the shoreline (including the Groton/Stonington snow hole). Snow to liquid ratios will be better than 10:1 with relatively cold soundings and some lift and saturation into the favorable dendritic growth zone. This isn’t a classic setup for good snow growth so I expect 15:1 snow:liquid ratios.

On a side note I couldn’t help but notice this National Weather Service map this morning. I generally don’t look at their forecasts or discussions but this really jumped out at me.

How the hell is this supposed to make any sense to anyone? A winter storm watch for Fairfield County and a winter weather advisory for the remainder of southern Connecticut. Nothing to the north? Why? Will Bridgeport get more snow than New Haven?  Snow should begin around the same time so why do we have watches, advisories, and nothing in effect when the storm appears ready to deliver similar impacts regionwide.

To be honest I don’t even know what the criteria is for each advisory or warning for each county because the definitions seems to change every couple years and they vary from county-to-county and state-to-state.

The NWS does a great job (most of the time) with severe thunderstorm and tornado warnings but maps like this do everyone a disservice. It makes no sense.


2 thoughts on “Saturday Snowstorm

  1. I think using county boundaries to delineate where weather effects stop and start is old-fashioned. Why not just use a simple map of CT with cities and towns, some highways and rivers, and superimpose the weather effects over them? Also, having three separate NWS offices divide up our little state leads to a disjointed forecast product.

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