12:00 PM Saturday | ***Powerful storm on the way for the eastern US with a wide-ranging impact to include snow, sleet, freezing rain, plain rain, coastal flooding, high (potentially damaging) winds***
Paul Dorian
A low-level jet streak will play a role in this upcoming event with high and potentially damaging winds possible; especially, along coastal sections of the Mid-Atlantic/Northeast US. Map courtesy NOAA, tropicaltidbits.com
Overview
An Arctic air mass poured into the northeastern quadrant of the nation in the overnight hours resulting in very cold and extremely dry conditions. At the same time, a vigorous disturbance in the upper atmosphere has pushed southeastward from the central Plains into the southern Plains. This system will edge into the Deep South by later tonight and surface low pressure will form in the northern Gulf region. On Sunday, the intensifying low pressure system will push northward through the eastern states with its expanding moisture field producing a wide range of impacts from snow-to-ice-to-rain. High (and potentially damaging) winds and coastal flooding will become an increasing concern with this storm on Sunday and impacts will last well into the day on Monday; especially, across the northeastern states.
12Z NAM forecast map of 500 mb vorticity field as of 7AM, Sunday with a strong upper-level disturbance centered in the southern US. Map courtesy NOAA, tropicaltidbits.com
Details
Dew point temperatures – a measure of total moisture content in the atmosphere – are very low today (sub-zero in many spots of the Mid-Atlantic/Northeast US) as is customary of a true Arctic air mass that poured into the region during the overnight on stiff northerly winds. Meanwhile, snow and rain has broken out this morning across the Mississippi Valley and this area of moisture will shift to the southern states later today and tonight. Low pressure will intensify in the southeastern states by later tonight and then begin a move to the north on Sunday morning bringing its moisture field along for the ride. As this moisture field encounters the cold, dry, dense Arctic air mass to the north on Sunday morning, a significant snow and ice storm will unfold for upstate portions of Georgia and the Carolinas. In fact, some of the higher elevation spots in this region of the country can get as much as a foot of snow and other areas can have a serious ice build-up.
Lots of colors on this surface forecast map for early Sunday evening with a range of precipitation from “ordinary” rain (green), heavy rain (yellow, orange), snow (blue) and sleet/freezing rain (purple/pink). Map courtesy NOAA, tropicaltidbits.com
By later Sunday, moisture from the intensifying storm will arrive in the Mid-Atlantic region and it’ll again encounter cold, dry, dense Arctic air in the lower levels of the atmosphere. As such, snow is likely to break out in the DC metro region during the mid-to-late afternoon hours and during the early evening hours in Philly and NYC - some front-end accumulations are quite likely. As the surface low pressure system moves northward, it’ll take on an inland track near or over Route I-95 and this will allow for milder air to push in from the western Atlantic Ocean riding in on east-to-southeast low-level winds. As a result, the DC-to-Philly-to-NYC corridor will see the snow transition to sleet and then to freezing rain and eventually to plain rain with above-freezing temperatures by late Sunday night. A word of caution, the icing can be for an extended period of time in the normally colder northern and western suburbs of the big cities as the cold, dry, dense Arctic air will be quite reluctant to give up its ground. Also, the plain rain late Sunday night can actually become heavy at times with a thunderstorm not out of the question in some spots.
On Monday morning, precipitation can actually change back to all snow in portions of the I-95 corridor before it ends as colder air likely wraps back around the system from northwest-to-southeast as the surface low pushes to the north. The heaviest snowfall amounts from this storm are likely to take place in the zone extending from far western Virginia/western Maryland/West Virginia northward to across western/central PA into western/central NY and interior New England.
There will be plenty of moisture available for this storm system including an influx from tropical air that will wrap into the system from the southeast of the storm center with a reach back way down in the low latitudes. Map courtesy NOAA, tropicaltidbits.com
In terms of snowfall amounts for the immediate DC-to-Philly-to-NYC corridor during the front-end of the storm, current estimates are as follows:
DC: 2-5 inches with the highest amounts in the immediate western/southwestern suburbs and the lowest amounts to the south and east of the District; some of the far western and northwestern suburbs could see as much as 6 or 7 inches of snow on the front-end of the storm before the mixing develops (e.g., Culpeper, VA, Frederick, MD)
Philly: 1-4 inches with the highest amounts in the far northwestern suburbs of Philly (e.g., Pottstown, PA) and the lowest amounts in the city and nearby spots south and east of there
NYC: coating to 3 inches with highest amounts in the far northwestern suburbs of the city
Coastal sections of New Jersey and the Delaware Peninsula: little or no snow accumulations are expected.
Another important factor with this unfolding storm will be the expected high and potentially damaging winds. A strong low-level jet will develop just a couple thousand feet off of ground-level as this storm reaches its full potential later tomorrow into Monday. As a result, there can be high winds gusts of 40-50 mph at surface level during the storm’s peak anywhere along the I-95 corridor and even higher gusts are possible along coastal sections of the Mid-Atlantic/Northeast US. The strongest winds will be from an east-to-southeast direction and this kind of air flow will likely lead to some coastal flooding issues at times of high tide on Sunday night and Monday. The threat of flooding will not only be along the Atlantic coastline (e.g., New Jersey, Delaware), but also around the Delaware and Chesapeake Bays (e.g., Annapolis, MD).
One final note, the overall weather pattern looks to remain quite a bit colder-than-normal in the central and eastern US as we go through the second half of January. There will very likely be additional winter storm threats including one perhaps around next Friday or Saturday (1/21-2/22). Some of the upcoming cold can be on the extreme side; especially, during the last full week of the month…get ready for some pretty ugly heating bills.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com