The new pattern we discussed last week seems to be holding itself nicely as we watch yet another storm system move into the region with heavy snow for the interior and a mixture of snow and ice for the coastline. Forming out west and moving eastbound, this winter storm will likely cause headaches for millions by the middle of this week. The major difference with this system compared to the last, seems to be the possibility of colder air holding on a bit longer, potentially expanding the region of snow and ice further towards the coastline on Wednesday morning.
Our winter storm will begin moving out of the western states later tomorrow, producing snow to the north across parts of the Plains and spotty shower and thunderstorm activity to the south across nearly all the southern states. As the two separate areas of convection begin merging together overnight on Tuesday across the Midwest, a high pressure to the east will allow cold air to remain in place. At this point light to moderate snow will start to fall from Chicago to Des Moines dropping a few quick inches of snowfall, while freezing rain begins further to the south across parts of northern Kentucky.
As the sun begins to rise on Wednesday morning, precipitation from the south will become heavier and expand well to the north as an elongated low pressure system starts to form between the two large areas of convection. Its around this juncture early on Wednesday morning where cold air from the Northeast will begin to recede and get replaced by warmer southern air. How quickly that happens will determine much of what ends up falling and accumulating from Washington DC to Philadelphia to New York to Boston. The quicker the escape, the less snow and ice, and vice versa.
Right now we’re leaning more towards our shorter-range, mesoscale models, as historically this set of computer model guidance is better at picking up on retreating cold air masses and cold air damming. With no real surprise, these are the models that have been on the colder side of the forecast thus far. Again if we take a look back at history when dealing with these types of storms, models (especially the longer-range global ones) tend to underestimate how long the cold air can hang on before moving out.
By 7 AM Wednesday morning we have decent agreement that moderate to heavy snow is falling over a good portion of Ohio and into western and central Pennsylvania. Major metropolitan cities like Washington DC and Baltimore also start to get in on the action around this time, with light snow, sleet and freezing rain beginning to fall. Heading into the 8 AM to 10 AM timeframe, precipitation fills in entirely, and snow begins falling from Syracuse NY to Scranton PA to Philadelphia.
As we move towards noon, we see a rather fast transition over to all rain for areas to the south of Philadelphia, with New York City on north managing cling on to snow and frozen precipitation longer. At this time State College PA to Syracuse to Burlington will still be in the thick of the storm, with heavy snow overspreading nearly all of western and central New England. Around 3 PM snow finally begins to wind down across western Pennsylvania and New York, but the worst of the freezing rain now begins moving up into higher elevations of northeastern Pennsylvania, northern New Jersey, and coastal Connecticut. That also won’t last long, as warm air continues to advance and anything frozen changes over to all rain south of Hartford CT (this should happen by 7 PM the latest).
While snow will be a major component of this storm, we’re beginning to become more concerned about widespread freezing rain as well. Assuming mesoscale guidance is correct in its most recent depictions, places stretching from southern Indiana, northern Kentucky and southern Ohio over towards the northern spine of the Appalachian Mountains (not too far away from Washington DC and Baltimore) will see the worst of the freezing rain, with up to a quarter of an inch not out of the question. Another area where we have to watch for moderate freezing rain is up towards northeastern Pennsylvania, northern New Jersey, northern Connecticut and even parts of extreme southern Massachusetts.
Why the freezing rain? These types of systems are pretty ideal for producing liquid in the air that ends up freezing at the surface. A storm originating from the south bringing warm air northbound will allow for (initially) warmer air to move overtop the colder and staler air at the surface. When precipitation falls it will melt a few thousand feet up, but hit <32 degree temperatures at the surface and begin to freeze.
Freezing rain won’t just be an issue for the areas we listed above, as a brief period is still expected outside of the moderate areas. We have concerns from Washington DC to Baltimore to Philadelphia and right up the I-95 corridor into New York and Boston. For the most part this freezing rain will accumulate a tenth of an inch or less, but even a coating of freezing rain can cause issues. After 12 PM, warmer air will filter down to the surface and allow most of those problems to disappear.
As northern New England begins experiencing the brunt of the heavy snow from the evening into the overnight hours on Wednesday, most other places to the south will begin clearing out. By sunrise on Thursday, we expect this system to be completely gone with fresh cold air ushering in behind. Another update on this system will be released tomorrow. Some changes could be possible with guidance catching onto colder air staying in place longer – Stay tuned.