12Z GFS forecast map for early Sunday morning during the "rapid intensification" phase of the "clipper" system; map courtesy tropicaltidbits.com, NOAA/EMC
Winter will not go away easily. After another cold, dry day on Friday, attention will turn to the next system that could bring some snow to parts of the Mid-Atlantic region between tomorrow night and early Sunday morning. Beyond that, there will be some modification in temperatures during the early part of next week, but then another significantly colder-than-normal air mass reaches us by the middle of next week.
12Z GFS forecast map for late Friday night during the "warm frontal" phase of the "clipper" system; map courtesy tropicaltidbits.com, NOAA/EMC
“Clipper” snow threat
The next system to deal with in the Mid-Atlantic region will be a “clipper” low pressure system that will drop southeastward from the Great Lakes region by early Saturday and then it’ll reform off the northern Mid-Atlantic coastline on Saturday night. There will be three different precipitation phases associated with this system that can be described as follows: 1) an initial burst of “warm air advection” precipitation on Friday night 2) “warm sector” precipitation on Saturday and 3) precipitation associated with rapid intensification of the low pressure system on Saturday night as colder air gets drawn in from the north.
The first phase of precipitation on Friday night associated with the advancement of a warm frontal system is likely to be in the form of rain south of the PA/MD border, but it can be rain and/or snow in the Philly and NYC metro regions and sleet is even a possibility. Small snow accumulations are possible north of the PA/MD border on Friday night as this first wave of precipitation takes place. On Saturday, any mixed precipitation is likely to change to all rain during this second phase as it turns somewhat milder following the passage of the warm front.
By Saturday night, rapid intensification of the low pressure system will take place off the northern Mid-Atlantic coastline and colder air will be drawn in from the north. As a result, steady snow or snow showers could break out along the I-95 corridor during this final phase of the "clipper" system and there can be small accumulations from Philly to NYC on Saturday night and perhaps even as far south as the DC metro region. In fact, if this system intensifies rapidly enough on Saturday night, there can be a few-to-several inches of snow in and around the NYC metro and all along the southern New England coastline. Any snow in the I-95 corridor that takes place in the final phase should come to an end by early Sunday morning.
12Z GFS forecast map of 850 millibar (~5000 high) temperature anomalies come Wednesday morning (3/22/17) with another well below normal cold blast for the Northeast US; map courtesy tropicaltidbits.com, NOAA/EMC
More cold coming
In addition to the threat for some more snow in parts of the Mid-Atlantic region, there will be at least one more significant cold air outbreak that arrives by the middle of next week and it could generate more records. Temperatures will modify some on Monday and Tuesday, but then another cold blast will arrive by Wednesday of next week and we’ll return to well below normal levels for this time of year. There are signs that this next cold blast won’t last too long, however, and we’ll finally get some warmer-than-normal conditions by the end next week.
Meteorologist Paul Dorian