Mar 25, 2014: Storm Slides Offshore, Cold Moderates

Forecast Highlights:

nerad25A low pressure about to undergo rapid intensification off the coast will produce snow mostly to the south and east, with light snow showers generally under 1 inch expected for parts of the NYC area. Windy conditions are anticipated behind the storm, with a more significant warmup for the late week as temperatures surge back into the 50s along with several rain events.




Tonight – Wednesday: Storm Departs, Cold/Windy Wednesday


Posted above from left to right are the latest available surface analysis and radar composite from WPC, and the 18z GFS 3-hour forecast 500 millibar heights and vorticity from NCEP MAG; both are valid at 21z (5pm). An upper level trough continues to become negatively tilted offshore, which earlier today aided in the development of a low pressure off the southeastern US coast. This low has since tracked NNE while beginning to rapidly intensify; as of the latest available data, there are two low pressure centers, one east of North Carolina and south of NYC, and the other low located further southeast, south of Cape Cod’s latitude. Both lows will consolidate later tonight as the trough closes off and continues to track NNE towards Nova Scotia, along with a dual jet structure with rapid acceleration near the left exit and right entrance quadrants, which favor nearly explosive deepening of the low pressure tonight. With the western ridge axis having flattened out and the 500mb low closing off too far east, however, the worst of the storm is staying east of the region, slamming Nova Scotia with over 1-2 feet of snow and strong wind gusts.

nerad25The latest regional radar imagery to the left, from the Pennsylvania State University e-Wall, depicts widespread moderate snow affecting the Delmarva Peninsula into southern NJ, where light to moderate snow accumulations have been reported so far. The precipitation shield will gain more of an easterly component over the next few hours as the low pressures consolidate further east and rapid deepening continues, with the western end of the heavy snow brushing Cape Cod and downeast Maine. This will spare the area of much snow, with most locations from NYC and north/west expected to see little, if any snow, with locations further east and south observing up to 1 inch, locally higher towards eastern LI/SE CT. As the storm departs overnight, a tight pressure gradient will develop across the region, leading to strong northwesterly winds on Wednesday up to 20-35 mph, with gusts up to 40-50 mph expected. High temperatures will peak in the low-mid 30s inland and mid to upper 30s elsewhere, with wind chill values generally in the 20s. Decreasing winds and cloud cover overnight will allow for temperatures to fall into the 10s inland and low-mid 20s near NYC and the immediate coast, with wind chill values mostly in the 10s.


Thursday – Beyond: Warming Up

As a more zonal flow develops across the US with a low pressure tracking into southern Canada, a warmer air mass will surge into the region, with highs on Thursday peaking in the low to mid 40s. Increased cloud cover is expected overnight with scattered showers on Thursday night into Friday as highs surge into the low to mid 50s. The model guidance is coming into better agreement regarding a low pressure moving through on Saturday but with uncertainty regarding the track; I am currently siding closer to the ECM with the low tracking north of the area, with highs remaining in the 50s with showers possible on Saturday into Saturday night, with some clearing possible for Sunday as the low shifts eastward. There remains some uncertainty during this time period and the outlook is subject to some changes.

The low pressure is then modeled to continue drifting east offshore, with the ECM and GFS supporting a significant warm up for Monday and Tuesday ahead of another approaching low pressure; the ECM, however, allows the warmth to surge into the region with highs in the 60s, while the GFS keeps the area and especially New England under the influence of a cooler air mass with highs mostly in the low to mid 50s. Given typical model biases in this time of the year, I am siding towards the cooler scenario with highs in the mid to possibly upper 50s, but with some changes possible. The next rain event appears to be towards the middle of next week but with details uncertain.

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