11:35 AM | **Coast-to-coast cold…small-scale snow event to watch for on Wednesday associated with a “norlun” trough…widespread accumulating snow event for the late week/weekend**
Paul Dorian
The 850 mb temperature anomalies for this afternoon feature “coast-to-coast” cold; courtesy NOAA/EMC, tropicaltidbits.com
Overview
Colder air moved into the Mid-Atlantic region in the overnight hours and the chill will remain in place right through the upcoming weekend. In fact, the nation is currently experiencing colder-than-normal weather virtually from coast-to-coast and this general pattern will continue for the next few days. In terms of storminess, one low pressure system over the western Atlantic on Wednesday may feature an inverted (“norlun”) trough extending back to the New Jersey coastline with the potential of small-scale heavy snow banding and another storm will approach the southern California/northern Baja California region late in the week from the eastern Pacific Ocean. This late week storm will then re-emerge over Texas by early Saturday and from there it’ll likely track towards the Carolina coastline. Given this track, significant accumulating snow will likely be the result from Oklahoma-to-North Carolina and even as far north as the southern part of Virginia. After that, it is still somewhat unclear as to whether this storm will impact the big cities from DC-to-Philly-to-NYC with significant snowfall, but that scenario is certainly still on the table.
12Z NAM surface forecast map for tomorrow afternoon with a “norlun” trough extending to the northwest of a low pressure center centered over the western Atlantic; courtesy NOAA, tropicaltidbits.com
Short-term…Atlantic Ocean storm and a ”norlun” trough
Temperatures reached the 50’s on Monday in DC, Philly and NYC, but that is likely to be the high mark for the week as colder air has moved in and there will be reinforcing cold shots over the next few days. High temperatures this afternoon will be close to the 40 degree mark and we’ll likely do no better than the 30’s on Wednesday.
12Z NAM forecast map at 500 mb for tomorrow afternoon with a vigorous wave of energy in the atmosphere over the Mid-Atlantic region; courtesy NOAA, tropicaltidbits.com
In addition to the cold, there will be unstable atmospheric conditions on Wednesday that could actually result in a small-scale snow event in portions of the Mid-Atlantic region. First, an impressive upper-level wave of energy will be moving overhead during the day on Wednesday and this will create some instability in the atmosphere. Second, surface low pressure will be intensifying off the east coast later tomorrow and there is likely to be an inverted trough extending to the northwest of the low pressure center all the way back to the New Jersey coastline. This type of trough is sometimes referred to as a “norlun” trough and it can create some tricky forecasting issues because of the potential for small-scale banding of heavy snow. As a result of all this instability, there can be some snow shower activity on Wednesday throughout the Mid-Atlantic region with heavier mesoscale snow banding associated with the “norlun” trough across central and southern New Jersey; especially, in coastal sections where snow accumulations of at least a few inches are possible. Reinforcing cold air will push into the Mid-Atlantic region on Thursday with the passage of another cold frontal system.
12Z NAM surface forecast map for Sunday afternoon with a strong surface low over the Carolina coastline; courtesy NOAA, tropicaltidbits.com
Late week/weekend…Pacific Ocean storm to the east coast
Late in the week, a storm will head towards the southern California/northern Baja region from the eastern Pacific Ocean and then this low pressure system will likely re-emerge over Texas by the early part of the weekend. From that location, all signs point to a general west-to-east track of this storm to a position near the Carolina coastline by the second half of the weekend. Given this track, copious amounts of rain will likely fall from in the Deep South later in the week and into the weekend and there can even be some severe weather to deal with in that part of the country. Farther north, along and just to the north of Route I-40, significant accumulating snow is likely from Oklahoma-to-North Carolina and the significant accumulating snow can even extend as far north as southern Virginia.
It is still unclear from this vantage point as to what kind of impact there may be in the DC-to-Philly-to-NYC corridor from this weekend storm, but the threat for significant accumulating snow is certainly still on the table in the Sunday/Monday time period. The current general consensus of computer forecast modeling is for this system to stay primarily just to the south of the I-95 corridor region; however, there tends to be a south and east model bias with respect to the positioning of east coast storms when several days out from event time. As a result, stay tuned…there is still plenty of time for this storm to shift to the north in model projections and there are atmospheric reasons as well, in my opinion, for this system to make a run up along the Mid-Atlantic coastline.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com
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