A quick hitting storm passes south of the city today bringing some rain and mixed precipitation, with no accumulating snow expected. Colder temperatures then take hold in the mid-30s behind this storm Tuesday as a strong area of high pressure builds over Quebec. This sets the stage for a potentially significant snowstorm developing Wednesday into Thursday with 8″+ totals possible along the I-95 corridor (with higher amounts north and west). However, there is still a good deal of uncertainty with the eventual track of this storm that could result in large differences in outcomes.

Rest of today – temperatures dropping through the low-40s into the 30s with mostly cloudy skies and a steady, chilly rain, possibly mixing with some wintry precipitation. No accumulation is expected. Overnight lows around the freezing mark with precipitation ending as high pressure begins building in.

Tuesday – proverbial calm before the storm as high pressure dominates, giving us a mostly sunny day with high temperatures around 40ºF. Overnight lows again in the upper-20s with cold northerly winds flowing around the east side of this high.

Wednesday – high pressure yields to a developing coastal storm. Partly sunny to start with increasing clouds. High temperatures in the mid-30s. Overnight lows drop into the mid-20s. The big story is the potential for a significant snowstorm with accumulations possibly over 8″. GFS and the Euro model have come into agreement for much higher totals, 14-15″. However, NAM shows a warmer scenario with warmer air working further north, thus cutting into overall totals (only 7″). It’s also possible that the low tracks close enough to shore that we end up with a good deal of rain mixing in at the coast, cutting snow totals even further.

Part of the energy fueling this storm is coming all the way from a shortwave with origins over the Pacific Ocean. This has only just made landfall in the US today. As this energy gets sampled by upstream soundings (weather balloon launches) and other means, the forecast models should get a better sense for how this storm will evolve. At this time, there’s enough uncertainty in the forecast to still not buy into any specific totals. If you look below, you can see there’s a lot of spread in the models in terms of the track of this storm. This then translates to a wide range in ensemble forecast totals. In addition, with a coastal storm like this, where there’s a lack of deep, Arctic cold air ahead of the storm, there’s a sharp gradient between areas where the event would be all snow vs. a mixed event. If you see the 24 hour probabilities of > 8″ accumulation, you can see that a 50 mile shift in the storm track further south and east would give us much higher chances for big snowfall totals, while a shift the other way could result in a bust on snow totals. Suffice to say, this storm will bear close monitoring today and tomorrow as more data comes in and models have a chance to digest it.

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Thursday – depending on the speed and track of the storm, we could see precipitation lingering into the morning hours, with additional accumulation possible. Highs should hover around the freezing mark. Overnight lows drop into the mid-20s with reinforcing cold air advection on the backside of the departing storm.