Chicago snowstorm headed toward the Mid-Atlantic

The snow has begun in Chicago, as what promises to be their biggest snowstorm of the season moves through. The fast-moving "Alberta Clipper" has already brought up to 10" of snow to Minnesota and North Dakota. These type of storms, so-named because they originate in Alberta and clip along at a fast forward speed, typically bring the Midwest moderate amounts of fluffy snow that is relatively easy to shovel. However, this Clipper is traversing through an atmosphere that is warmer than usual for these types of storms--close to the freezing point near the surface. Since warm air can hold more moisture, this Clipper is bringing heavier snowfall amounts than is usual for a Clipper, with 4 - 8" of snow expected in Chicago. The storm, dubbed Winter Storm Saturn by The Weather Channel and "Snowquester" by The Washington Post's Capital Weather Gang, is expected to bring a swath of 4 - 8" of snow into the Mid-Atlantic through Wednesday, with the heaviest snows in excess of a foot falling in Western Virginia and eastern West Virginia. The models are still in considerable disagreement on what will happen to the storm on Wednesday, both in regards to the track and the location of the rain/snow line. I still prefer the European model's solution of a colder and more southwards-moving storm, which would likely bring Washington D.C. 4 - 8" of snow, their biggest snowstorm since January 26, 2011. There will be a sharp gradient in snowfall amounts in the region, though, due to the fact the rain/snow line will be in the area. We cannot rule out the solution provided by NOAA's SREF model, which calls for snowfall amounts closer to 15" in D.C. The Capital Weather Gang has an interesting article on historical March snowstorms in Washington D.C. In order for Snowquester/Winter Storm Saturn to crack the top-ten, it would have to dump at least 6.6" of snow on the nation's capital. The New England coast from Long Island to Southeast Massachusetts could also see heavy snows in excess of 6", though the uncertainty in snow amounts is high. There will be a very sharp gradient in the precipitation amounts, and the storm's track may keep the heaviest snows just offshore.


Figure 1. Predicted snowfall amounts from Winter Storm Saturn (AKA Snowquester) from the NWS. There is a sharp gradient in snowfall amounts near the coast, due to some of the precipitation falling as rain.

Coastal flooding a concern in the Mid-Atlantic and New England
As the storm moves off the coast on Wednesday night, winds gusting to 55 mph will build waves of up to 15' and a 2 - 4' storm surge along the coast to the north of the center, along the coasts of Delaware, New Jersey, and New York. Heavy rains will bring runoff down rivers that will act to increase water levels along the coast. The latest Forecast Discussion from the Mount Holly, NJ NWS office highlights the likelihood of moderate coastal flooding in Delaware during the high tide cycles on Wednesday afternoon and Thursday morning. The latest storm surge forecast from the GFS model calls for a storm surge of around 3' at Lewes, Delaware on Thursday morning, though the peak surge is currently forecast to hit at low tide, which would not bring top-ten highest water level on record to the coast. Still, even moderate flooding would cause much greater erosion than usual, due to weakened state of the dunes from the pounding Hurricane Sandy gave to the coast in October. Sandy brought the 3rd highest water level on record to Lewes. Moderate flooding is also expected along large portions of the New England coast, from New York City to Boston. Should the more northerly track of the GFS and NAM models verify, Southeast Massachusetts could be looking at a dangerous coastal flooding event with impacts far worse than experienced during Winter Storm Nemo on February 9.

We'll have ongoing coverage this week of Winter Storm Saturn in our Winter Storm Section.

Jeff Masters