12:15 PM | ***Relatively minor event tonight…major storm this weekend with rain, ice, snow…quick thumping of snow possible at the onset later Saturday in areas north of the PA/MD border***

12Z NAM forecast map of upper-level “frontogenesis” late Saturday evening and this raises a red flag that there could be strong upward motion north of the PA/MD border; courtesy NOAA/EMC, tropicaltidbits.com

Overview

There will be three different systems to deal with in the Mid-Atlantic region during the next week or so with a relatively minor storm tonight and then a major storm this weekend. Yet another storm could impact the Mid-Atlantic region with rain and/or snow by the middle of next week. Tonight’s system is likely to result in a coating to an inch or two in the DC-to-Philly-to-NYC corridor with the higher amounts to the north and west of Route I-95 and lesser amounts to the south and east.  A major storm will bring lots of precipitation to the Mid-Atlantic region this weekend with everything on the table from heavy rain to accumulating snow and accumulating ice.  An Arctic blast will flood the region on the heels of the storm late in the day on Sunday and this could result in a quick freeze-up and potential hazardous driving conditions.  Single digit lows are likely by early Monday morning and the coldest day of the year so far will likely see temperatures struggling to get out of the teens in the I-95 corridor.

Current radar loop featuring precipitation over the Midwest that result in snow tonight for much of the Mid-Atlantic region and widespread precipitation across the western US (snow=blue, rain=green, ice=pink); courtesy WSI, Inc. NOAA

Relatively minor event tonight, but…

A weak cold front has slid through the region in the last few hours and it has ushered in drier air (dew points have noticeably dropped) and temperatures will hold nearly steady for the rest of today as clouds thicken.  Snow may break out at the end of the afternoon in the DC metro region and then in all areas early tonight and it’ll continue through the night with a coating to an inch or two by morning.  As the precipitation winds down late tonight, there could be a brief period of sleet and/or freezing rain.  While this is a relatively minor event when compared to the potential of the weekend storm, watch out for slippery spots overnight and into the early morning hours on Friday as untreated roads will likely get covered.  Temperatures may then actually rebound to 40+ degrees in the afternoon on Friday as some sunshine returns to the region. 

12Z GFS forecast map for Saturday morning with high pressure over SE Canada and low pressure over the Midwest; courtesy NOAA/EMC, tropicaltidbits.com

Weekend storm

A major storm this weekend will bring lots of precipitation to the Mid-Atlantic region with everything on the table in the immediate I-95 corridor from heavy rain to accumulating snow and accumulating ice.  In general, as with many winter storms in the Northeast US, more snow and ice will fall to the north and west during this upcoming event and more rain to the south and east.  In fact, the interior higher elevation locations from upstate PA to northern New England can end up with 1-2 feet of snow this weekend when all is said and done.  As per usual, the I-95 corridor region is likely to be a “battle zone” with all precipitation types possible from rain-to-sleet-to-freezing rain-to-snow. 

By the early part of the weekend, low pressure will be intensifying over the Tennessee Valley region and it’ll feature lots of snow to its north and west and rain to the south and east.  At the same time, an important factor will be strong high pressure that will be building over southeastern Canada and this will push a reinforcing cold, dense air mass into the Northeast US.  It is likely the surface low pressure system will advance as far north and east as West Virginia this weekend before jumping towards the Mid-Atlantic coastline and this projected storm track is critical and still not set in stone (see below).

12Z GFS forecast map for Saturday evening with high pressure over SE Canada and low pressure over West Virginia courtesy NOAA/EMC, tropicaltidbits.com

Precipitation could arrive in the I-95 corridor by the mid-to-late afternoon hours on Saturday and with the reinforcing cold air mass in place, a wintry mix could break out south of the PA/MD border and moderate-to-heavy snow to the north across PA, NJ and NY.  I am increasingly concerned that much like the November snowstorm, the low-level cold air may be very reluctant to give up its ground at the onset of this storm later Saturday which could result in a quick thumping of accumulating snow across much of PA, NJ and NY (i.e., a few-to-several inches on the table).  There will be tremendous “frontogenesis” late Saturday in those areas north of the PA/MD border (see 12Z NAM forecast map) and this could contribute to a quick thumping of snow.  In the DC metro region, the wintry mix may hang on for a bit as well, but a changeover to rain is likely by late Saturday. 

On Saturday night, precipitation may continue as rain south of the PA/MD border and either a wintry mix or rain north of there.  On Sunday, cold air will be advancing southward as the storm pulls to the northeast and any rain that is falling in the DC-to-Philly-to-NYC corridor is likely to change to ice and/or snow before the precipitation winds down completely.  On the heels of the storm later Sunday, an influx of Arctic air will cause a plunge in temperatures and this could lead to a quick freeze-up with the potential of hazardous driving conditions.  In fact, temperatures are likely to drop all the way into the single digits by early Monday morning so any slush or leftover wet spots will freeze solid in the overnight hours.  High temperatures on Monday – which will be the coldest day of the year so far – will struggle to escape the teens in much of the I-95 corridor.

12Z GFS forecast map of low temperatures on Monday morning; courtesy NOAA/EMC, tropicaltidbits.com

Factors still to monitor

One factor to continue to monitor over the next couple of days is the cold air intrusion into the Northeast US that should take place on Friday night and early Saturday as strong high pressure builds into southeastern Canada.  If this reinforcing shot of cold air is a bit stronger than currently projected then there could be more snow and/or ice at the onset later Saturday – perhaps even in areas to the south of the PA/MD border.  In general, computer forecast models tend to underplay the magnitude of low-level cold air intrusions this time of year and can erode the cold air too quickly.

In addition, the main driver of the weekend storm is a vigorous upper-level feature that is contributing to the pounding that California is now getting with tremendous rains along the coast (5+ inches) and pretty amazing snows at higher elevation locations inland (e.g., 5-10 feet in the Sierra Nevada Mountains).  This upper-level system will eventually trek across the country and slowly “dig” southward as it heads across the south-central US.  If this system drives a little more to the south and east than currently projected, then the storm track would likely also end up a little bit farther to the south and east and this could result in an overall colder solution for the Northeast US (i.e., snow and ice over a larger area).  Stay tuned.

Courtesy Twitter

On the lighter side

As some of you may know, the Weather Channel actually names winter storms and they have used “Harper” for the weekend storm that is currently pounding the western US.  Could this be an omen that Bryce Harper is about to sign with the Phillies (of course, Nationals fans may think it’s an omen that he’ll stay there)?

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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