The initial storm on Monday will have “marginal” cold air to work with in the Mid-Atlantic/Northeast US likely resulting in a combination of rain and snow. The most likely scenario on Monday is for primarily a rain event to occur in the big cities and in coastal locations. However, the rain is likely to change over to accumulating snow in some of the suburbs to the north and west of I-95. In the DC metro region, the changeover to accumulating snow may be limited to the far northern and western suburbs, but in the Philly and NYC metro regions, nearby suburbs to the north and west can end up with accumulations of up to a couple of inches or so. All of this activity on Monday is likely to be just a “teaser” event when compared to what could come at mid-week.
A second disturbance will cross the southern states on Tuesday and head towards the Mid-Atlantic coastline for a mid-week rendezvous. This second system will be able to gather plenty of moisture from the Atlantic Ocean and Gulf of Mexico and the cold air source to the north (i.e., strong high pressure over southeastern Canada) will become better established by then as compared with tomorrow’s initial storm system. As a result, the chances for significant accumulating snow will increase in the Mid-Atlantic/Northeast US for the mid-week storm system. In fact, this system has the potential to produce more snow seen in several years in at least parts of the Mid-Atlantic/Northeast US where major snowstorms have been rather limited in recent years (last major one in the DC-to-Philly corridor was January 2016).
One final note, “climatology” does suggest that it is quite difficult to get significant accumulating snow in the big cities along the I-95 corridor during mid-December with the still relatively-warm sea surface temperatures in the western Atlantic Ocean. The climatological limitations this time of year are certainly something to be cognizant of; however, significant snow events have taken place in the month December. One way for such an event to take place is with “high-latitude blocking” in the upper atmosphere and strong surface high pressure anchored to the north – both of which are likely for mid-week.
Stay tuned…certainly an interesting weather pattern for the upcoming week.
Meteorologist Paul Dorian