John Homenuk

Coldest air of the season arrives Monday Night

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With news of an impending rain storm and warmup on Monday, hope may be rising for increasingly pleasant weather during the next week. That hope will come crashing down as quickly as Monday Night, along with temperatures throughout the forecast area. An arctic blast, straight out of Canada, will rush into the area on Tuesday behind Monday’s storm system, bringing the coldest air of the season into the area.

Forecast models have been consistent in hinting at this potential for 7 days or more, but are just now beginning to focus in on the intensity of the cold air. Anomalous and impressive, the cold air will surge in from Central Canada. First into the Ohio Valley, and then into the Northeast — straight to the coast

The culprit? A ridge of high pressure which originates all the way on the West Coast of the United States. Surging into British Columbia and Alaska, the ridge has brought record warm temperatures there. But it is also dislodging cold air, typically bottled up over Canada, to the south. And with a storm system moving through the Great Lakes on Monday, that cold air — already moving southward — will be sling-shot east through the Ohio Valley and toward the East Coast.

GFS model's height anomalies at 500mb this week. A large ridge on the West Coast has displaced lower than normal heights over the Eastern US.

GFS model’s height anomalies at 500mb this week. A large ridge on the West Coast has displaced lower than normal heights over the Eastern US.

While not record shattering in terms of “winter cold”, the airmass will be quite impressive for this time of year. With clear skies and relatively light winds on Tuesday Night, forecast models show temperatures falling into the teens across a majority of the forecast area, even in the urban corridor of New York City and Philadelphia. The surge of cold will actually begin on Monday Night, behind the cold front associated with the low pressure system bringing rain to the area.

NAM-WRF model forecasting low temperatures in the teens and 20's from Tuesday Night into Wednesday morning.

NAM-WRF model forecasting low temperatures in the teens and 20’s from Tuesday Night into Wednesday morning.

But westerly winds will continue through Tuesday, and temperatures at 850mb will fall to nearly -20 C during the afternoon on Tuesday through Wednesday morning. Highs on Tuesday may not reach out of the low to mid 30’s. And by Wednesday Night, with the anomalously cold airmass settled into place, radiational cooling will do its work and temperatures will, most likely, fall into the teens throughout the area.

The good news? By late week, temperatures will moderate a bit. The bad news? The pattern will continue to be active, with continued shots of cold and — eventually — the potential for snow.