Cold, dry weather through weeks end

After the first snowfall of the season on Tuesday, low temperatures fell into the single digits and teens throughout the area by early Wednesday morning. The arctic airmass settling into the area on Wednesday will stick around through the second half of the week, bringing high temperatures down into the upper 20’s and lower 30’s on Thursday. Although there won’t be any harsh biting winds, the snowpack over the interior will make it feel especially cold and will help with radiational cooling during the overnight hours. 850mb temperatures will fall to near -20 C on Thursday afternoon, and temperatures in the teens should be common each morning towards the end of this week.

The calm weather pattern will come as a bit of relief after several days of active weather with a front near the area. Owing to a dominant high pressure over the Northeast US, plenty of sun is likely on each day as we roll towards the weekend. But by the forthcoming weekend, intrigue will again increase as another mid and upper level disturbance tracks from the Central United States towards the Northeast and Mid Atlantic. As a result of this disturbance, a low pressure system is forecast to initially track towards the Ohio Valley. Eventually, a secondary low pressure will redevelop to the east, forced to do so by a strong high pressure to the north and cold air holding firm over New England. The devil is in the details with this system, as the uncertainties suggest potential for a winter weather event, but incredibly low confidence.

NAM model showing low temperatures in the teens on Friday morning.

NAM model showing low temperatures in the teens on Friday morning.

Forecast models are struggling, still, with the placement and strength of the redeveloping surface low as well as the strength and track of the primary low. This obviously will have major implications on the forecast in our area, and as such precipitation amounts and type remain highly uncertain. Should a stronger primary surface low prevail, initial cold air would provide a period of frozen precipitation but would eventually be pushed out and overcome by warmer air both aloft and at the surface. Should the secondary low redevelop faster, stronger, and farther south — colder air would remain entrenched in the area, increasing the probability of a winter storm with plenty of snow, sleet or ice.

Additionally, the exact timing of this high pressure system is important, which somewhat correlates to the strength of the primary low. If that high pressure in SE Canada slides out to sea too quickly, it will help to bring milder easterly winds off of the Atlantic Ocean and change our area to rain, and provide a pathway for the storm to cut to our west. If the high pressure can work its way into SE Canada a bit later and slow down, then it will be directly overhead when the heavier precipitation is arriving, which leads to the potential of a strong frontogenesis-forced snow band, like the Philly area saw on December 8th — only this time, it would be more expansive due to the storm’s moisture source being a bit more organized. This would also force secondary redevelopment to the south.

GFS model showing mixed precipitation impacting the area this weekend as a storm system moves off the Mid Atlantic coast.

GFS model showing mixed precipitation impacting the area this weekend as a storm system moves off the Mid Atlantic coast.

All of these scenarios remain on the table at this juncture, and confidence in any one of them remains rather low. Without any true high-latitude blocking, it’s hard to imagine the scenario playing out where the entire area (including the coast) sees a major snowstorm. But confidence in an event alone seems to be rapidly increasing, with forecast models coming into agreement on the disturbance, which will have plenty of moisture and run into a good, pre-existing cold airmass — which may give some of the area snow, even if the storm ultimately takes an unfavorable track for snow and changes the area over to sleet, freezing rain and rain.

Stay tuned over the next few days for further information as we continue to analyze the potential.

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