Ice and snow to threaten the Northeast January 17-19...
Sunday night will feature the approach of a high pressure system located north across New York State. Stable air will eventually bring an end to the significant lake effect snow squall near Oswego County on eastward with reports of over 12in of snow. With some radiational cooling, low temperatures will drop to the lowest of the season for many areas from Maryland to Maine. The coldest temperatures will be associated near the heart of the high pressure over upstate New York with -20F lows are possible towards Saranac Lake.
The 18z GFS 2m charts even show lows around -14F for upstate New York with negative teens as far south as northern Pennsylvania. Up towards northern New England a mid level cirrus deck and a slight northwest wind will prevent ideal radiational cooling. For southern areas towards southern Pennsylvania, Maryland, and Delaware lows will be in the teens in the urban areas to single digits over the rural regions. High level cirrus clouds will begin to stream northeast from the southwest ahead of an approaching storm system.
A deep -3SD trough over the northern Plains will be dropping south out of Canada with associated 1020mb high pressure. This deep trough is digging rapidly across the central United States with associated shortwave developing along the eastern periphery of the trough. This primary low will track northwest into Minnesota and will gradually shear apart as a second low redevelops south across northern Florida. Another double barrel low storm system will plague the east coast. Increasing PWATs will rise in the Middle Atlantic ahead of the low pressure developing off the North Carolina.
A southerly flow aloft will help to migrate the H85 0C line northward along with a sharp mid level above freezing deck. The high pressure over New York State will lift quickly to the northeast positioning itself just east of Nova Scotia. Warm air advection will aid in some light snow developing across northern Virginia moving northeast. The anomalous southerly flow will quickly change the light snow in Virginia and Maryland over to sleet and then freezing rain as the troposphere warms from top to bottom. By late Monday night the light snow will push north of the Mason-Dixon line. Some UVV and frontogenic support will cause a period of moderate snow for those along and north of the Pennsylvania turnpike early Tuesday morning with a quick burst of 1-2in of snow. Some locations towards the southern Poconos may even see a quick 3in of snow by the Tuesday morning commute. The H85 0C thermal will quickly progress northeast over into northern Pennsylvania and northern New Jersey. Again the warm air advection snow will give most areas a quick 1-3in of snow before the changeover to sleet and freezing rain. Current GFS SKEWT T charts indicate surface temperatures to remain below freezing especially for areas just northwest of I-95 from northern Maryland on northward.
The SKEWT T chart above is for KMDT during the height of the precipitation. Keep in mind the bold white line on the right is the temperature in Celsius. The surface around 1000mb is below freezing with rising temperatures with increasing altitude.
Cold air is denser than warm air and will likely hang on aloft a big tougher across New England. Current GFS/NAM prognostics indicate a burst of moderate to heavy snow near Albany and drawing a line eastward. Along the line and northward, a quick 2-6in of snow will occur before a changeover as temperatures warm aloft through New England. Current model surface maps indicate most of the heavier QPF over eastern areas especially in coastal regions of New Jersey up through southern New England where 1in QPF is possible. Model guidance supports a east-northeast wind at the surface. This often will lead me to believe that the cold air persists for inland areas longer than expected and couple that with the fact of a widespread snow park from northern Maryland on northward. I do not buy the quickly rising 2m 0C line advertised on the ECMWF and NAM. I think a major of the precipitation will be freezing rain along a line from Harrisburg to Allentown to Stroudburg to White Plains to Tolland to Worcestor. While QPF will be lighter in these areas, even .1-.2in of freezing rain can cause problems. With ground temperatures well below freezing from the antecedent cold air, non-treated surfaces will continue to freeze over even as boundary layer temperatures rise to 33-35F. For coastal areas and along I-95, most of the precipitation will be rain after a quick 1in of snow/sleet especially north of Philadelphia. The heaviest QPF will be over this region with rapidly decling amounts as one heads west. SREF means indicate only .1-.25in for many areas west of I-81. Eventually by Tuesday evening the surface low, 996mb, will move northward over Rhode Island and Massachusetts allowing surface temperatures to rise above freezing outside the higher elevations in the Berkshires where ice could be significant.
The highest risk of freezing rain is across northwest Connecticut, central Massachusetts. Also western Massachusetts up through New Hampshire, Vermont, and Maine will be at the highest threat for over 4in of wet snow.
A weak shortwave will rotate through as the cold front passes and the H85 0C line progresses west. The high resolution NAM is showing a light area of .1-.2in of QPF associated with this wave progressing through parts of the northern Middle Atlantic in Pennsylania. At the current time, it looks like it will be light rain especially for eastern areas, but I cannot rule out a 1-3in snow for some areas in western and central Pennsylvania with this shortwave.
Overall it appears a moderate accumulation (3-7in) is likely for the higher elevations of northern New England with moderate (.1-.25in) of freezing rain along the foothills of the Appalachians from Harrisburg on northeast up through central Massachusetts. The heavier QPF will be east towards the metropolitan region where 1in of rain is possible from Washington DC up through New York City. My map below gives a rough estimate on totals for this event. Given the complexity of the precipitation types, it is difficult to make a generalized map. Keep in mind snow totals will likely be a bit higher than I show on the map for northern New England. Also western Pennsylvania and western Maryland will likely see 1-3in of snow with the shortwave that will move through Wednesday along with some lake effect snow.
The current operational ECMWF shows a significant coastal cyclone affecting the region towards next weekend. The model though has little support from other guidance including the ensembles. But it does appear a wave will be ejecting out of the southern stream in the time frame; stay tuned!!!
"Here northeast of Harrisburg 2010-2011 winter statistics"
Current Snow Cover- 2-4in
Monthly Total (November)- Trace
Monthly Total (December)- 0.6in
Monthly Total (January)- 11.65in
Seasonal Total- 12.25in
Winter Weather Advisories- 5
Winter Storm Warnings- 0
Ice Storm Warnings- 0
Blizzard Warnings- 0
Freezing Rain Advisories- 1
Winter Storm Watches- 1
Lowest High Temperature- 24.1F
Lowest Low Temperature- 12.8F
Wind Chill Advisories- 0
Wind Chill Warnings- 0
(Snow Storms Stats)
First accumulating snow - December 10 - 0.50in
Clipper light snow - January 7-8 - 2.25in then another 1in
Double Barrel Low - January 11 - 4.5in of snow
Coastal Low - January 17-17 - 1.8in of snow/sleet
Arctic Front - January 20-21 - 2.1in of snow
Lower Susquehanna Valley Doppler...
(Courtesy of WGAL)