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Frigid Finish For February, Then March Starts Stormy

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(credit: CBS3)

(credit: CBS3)

PHILADELPHIA (CBS) – Reinforcing blasts of cold air will move through the area for the remainder of the month of February, dragging temperatures well below normal. It’s a fitting end to what has been a harsh winter month so far!

A strong arctic cold front will sweep through the area Thursday afternoon, bringing the chance for some flurries, but the wind is what will really signify the frontal passage – behind the front, winds will howl in the afternoon, with gusts peaking at over 30mph.

Friday morning’s forecasted low is just 10 degrees, and the record low is 9 – a clear indication of just how abnormal this airmass is. As for Friday’s high? A mere 22 degrees, around 25 degrees below average for the time of year. For reference, this is roughly the same temperature departure from normal that we felt with the first instance of the so-called “polar vortex” in early January.

Temperatures try to moderate as we start the weekend and the month of March, but a storm system swinging in to the West Coast will bring a renewed threat for winter weather starting on Sunday. It begins with another arctic cold front dropping in from the north and west. The extent to which this cold air sinks southward will be the key for determining the impacts with our next storm. This is not a coastal storm or nor’easter, but rather an area of low pressure that will ride along the boundary between cold, dry polar air to the north and very warm, moist Gulf air to the south. This will cause these two air masses to converge, or come together, and will cause the warm air to ride up over the cold air, a process known as “overrunning”. The clash of these two drastically different air masses will lead to convection, causing heavy precipitation. There is also a lot of moisture involved with this system, so anything that does fall has the potential to be heavy.

Precipitation type is going to be the biggest issue in forecasting this storm. As of this writing, we have several different model solutions on this. The most consistent guidance suggests that this may start as a mix of snow and rain, but then gets cold enough that it changes to mainly snow, mixing at times with some sleet or ice. If this were to happen, it could mean heavy snows for portions of the area, with the threat for significant icing, especially from I-95 south. An overrunning setup does produce a great risk for ice, because if the cold air stays planted at the surface while warmer air moves in aloft, the precipitation will fall as rain but freeze on contact in the colder surface temperatures.

Another solution, presented today by the European model, keeps the crux of the arctic air to our north on Sunday, meaning that the warm Gulf air is able to make more of an inroad across our area. This would mean the predominant precipitation type would be rain, possibly ending as a brief thump of snow.

In our area, in the wake of the ice storm we already endured, we want to root for either a very warm or very cold scenario. All rain or all snow would be preferable to marginal temperatures and the threat for ice. Regardless, this system has a lot of moisture and cold air to work with, and from the arrival of the arctic front Sunday through the system’s departure early Tuesday, it’s a long-duration storm providing a very messy start to next week for the entire area.

One additional note: be wary of snow maps posted on social media showing snowfall amounts. It’s certainly true that a couple of models have posited a 12″+ snow solution for this storm. It’s equally true that some of those same models predicted big snows for today, and for last week, and for other storms this winter that didn’t pan out. While a major snowstorm is certainly a possibility, a lot can change with a system like this 4-5 days out and thus, remember that one model’s output is not the final forecast.

Kate

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