Mar 24, 2014: Light Snow Likely Tuesday Night

Forecast Highlights:

f48An anomalously strong low pressure for this time of the year will rapidly develop east of the region on Tuesday into Tuesday night, but will remain far east enough to keep the heavier snows south and east of the area. Following the departure of the storm, occasional temperature swings are expected but with a gradual uptrend in temperatures as the long lasting winter slowly comes to an end.

 

 


 

Tuesday – Wednesday: Light Snow Expected

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Posted above from left to right are the latest available surface analysis and radar composite from WPC, and the GFS initialized 500 millibar heights and vorticity from NCEP MAG; both are valid at 18z (2pm). Generally dry conditions with little cloud cover were observed across the region today but with temperatures well below average as an anomalously cold air mass for this time of the year entered the region, with morning temperatures mostly in the low 20s and highs in the low to mid 30s. Central Park’s high temperature of 35 degrees was 17 degrees below average, only further cementing this March’s status as a much colder than average month, yet remarkably with below average snowfall due to every snowstorm remaining north or south of the area; average March snowfall is 3.9″, while actual observed snowfall this month is only at 0.1″. While additional snow is expected over the area on Tuesday as a low pressure explosively deepens offshore, this storm will prove to be no exception to this month’s trends, with most of the snow again remaining south and east of the area.

As previous updates have noted, this storm will form as a result of the interaction of multiple shortwave troughs; one in Kansas, another near North Dakota, and the northernmost shortwave over northern Manitoba in Canada. With the aid of a transient ridge over the western US amplifying the upper level flow, these shortwaves are anticipated to interact and phase over the next 24-36 hours as the trough axis becomes negatively tilted off the coast, which along with a dual jet structure consisting of rapid acceleration near the left exit and right entrance regions, acting to increase upper level divergence, will result in a low pressure explosively deepening offshore, reaching a minimum pressure of nearly 955-960 millibars while reaching New Jersey’s latitude. With strong upward vertical motion and a cold air mass, this storm will be capable of producing very heavy snowfall and strong wind gusts to the north and west of the low pressure center, which will primarily affect Nova Scotia. With a relatively progressive flow as the western US ridge flattens out and the phasing occurring too far east, however, the storm will spare the region of its most significant impacts except for Cape Cod and downeast Maine, which may fall under the western end of the heavy banding with blizzard conditions.

While most of the precipitation associated directly with the coastal low will remain offshore, some snow will still affect the region, particularly the Mid Atlantic as the shortwave trough in the northern US reaches the region, aiding in the development of precipitation with the best forcing and upward vertical motion generally south of SE PA into south-central NJ. The main uncertainty is how far north the snow extends; at this time, this round appears likely to mostly remain south of the area. Assuming this scenario verifies, light snow showers would be expected from the late afternoon through the early-mid overnight hours, with surface temperatures in the low 30s for most, initially near the mid 30s in NYC, which along with light precipitation rates would generally support snow accumulations slightly below the standard 10:1 ratios, with around 1-3″ from central-eastern LI into SE CT and less than/up to 1″ elsewhere, perhaps locally higher. Some slight uncertainty remains, and the main bust risk at this time would lead to the evening snow extending further north than currently forecast with more widespread accumulations of 1-2″ west of NYC and 2-5″ further east.

 

Longer Range: Temperatures Gradually Trend Upward

As the storm departs the region, cold temperatures will initially stick around on Wednesday with mostly cloudy skies, highs in the mid to upper 30s, and a NW wind at 15-30 mph with gusts up to 30-40 mph. The upper level trough will then exit with more significant warm air advection as a low pressure approaches southern Canada, with highs climbing into the low to mid 40s on Thursday, followed by occasional showers on Friday with highs in the mid to upper 50s. A slight cool down is anticipated for Saturday and Sunday with highs back into the low 50s. The latest model guidance indicates a more significant warm up for early next week with high temperatures surging possibly well into the 60s, although this time of the year is well known for backdoor cold fronts which prevent the warmth from extending into New England and occasionally the area, and this potential will continue to be monitored. The next possibility for widespread precipitation, likely to be in the form of rain, appears to be towards the middle of next week.

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