Mar 26, 2014: Cold Moderates, Rain Returns

Forecast Highlights:

gfs_3.26A strong low pressure underwent explosive intensification off the coast today, brushing coastal locations with light snow but with otherwise windy conditions and well below normal temperatures. As the system departs, however, a more sustained warm up is expected to arrive, initiating the most sustained warm up of this spring thus far. Temperatures will mostly remain in the upper 40s and 50s through the foreseeable range, along with some rain on Friday and possibly heavier rain on Saturday and Sunday as a slow moving low pressure tracks through the region.

 

 


 

Tonight – Friday: Quickly Warming Up

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Posted above from left to right are the latest available surface analysis from WPC, and the 18z GFS 3-hour forecast 500 millibar heights and vorticity from NCEP MAG; both are valid at 18z (2pm). Since yesterday evening’s update, when two low pressure centers were present east of North Carolina with minimum pressure around 997mb, the upper level trough became negatively tilted and closed off, which along with an impressive dual jet structure aided in explosive intensification of the low pressure late last night and through today as the low pressure centers consolidated and continued to track northeast towards Nova Scotia. Pressure falls were most significant between 6-12z (2-8am), when according to the Weather Prediction Center (WPC) surface analysis, the minimum pressure fell a remarkable 20 millibars in only 6 hours, exceeding the criteria for explosive intensification of a pressure fall of 2.5mb per hour. As of 2pm, posted above, the low pressure was east of Cape Cod with a minimum pressure near 955mb, an anomalously low minimum pressure for a non-tropical cyclone this close to the region for this time of the year; such intense mid-latitude cyclones and rapid deepening rates are more common further northeast, towards Atlantic Canada.

As phasing occurred too far east, however, the snowfall and strong winds associated with the storm remained south and east of the area, with Nova Scotia experiencing the worst direct impacts. Cape Cod was near the western fringe of the heavy banding, with Nantucket having reported heavy snow for several hours with a peak wind gust of 81.7 mph. An initial round of snow stayed south of the area, affecting Mid Atlantic region near Delaware and southern NJ, continuing the trends of this month keeping snow events north, south and east of the area, with temperatures in NYC below average this month but with very little snowfall. Despite the snow staying south and east, windy conditions were observed with a strong pressure gradient, with a northwesterly wind generally between 20-30 mph with gusts up to 40-50 mph. Temperatures peaked in the mid to upper 30s, at least 15-20 degrees below average.

The low pressure will depart later tonight with weakening winds becoming nearly calm by Thursday morning, but with clearing skies supporting temperatures falling into the mid-upper 10s for most of the area away from NYC and the immediate coast, where lows in the low-mid 20s are expected. As the upper level flow turns more zonal with a low pressure approaching southern Canada, a stronger southwesterly flow will develop both at the surface and aloft, allowing for warmer temperatures to quickly make a return into the region; mostly sunny skies are expected for Thursday with highs in the low-mid 40s, with overnight lows struggling to fall below the low-mid 30s before climbing into the mid-upper 50s on Friday as the cold front associated with the low pressure to the north passes through, with scattered showers expected mainly in the afternoon and evening.

 

Saturday – Beyond: Rainy Weekend, Some Warming Expected Next Week

Yesterday’s models began to depict a low pressure affecting the region with significant precipitation with more consistency, which continued through today’s runs with somewhat better agreement regarding the depiction of a shortwave trough entering the NW US on Thursday and continuing to progress east with the mostly zonal and progressive flow. With rising heights aloft expected over southeastern Canada ahead of another approaching shortwave over the Midwest and a strong upper level low near central Canada, the low pressure will slow down as it approaches the region and is expected to cut off while located offshore, leading to occasional periods of rain affecting the region on Saturday and Sunday. With the low pressure cutting off from the main flow and thus from a source of a fresh cold air mass, temperatures will remain warm enough to support widespread rain across the region, gradually changing to wet snow in the higher elevations of New England, but with a widespread major snow event unlikely at this time and with the higher probability of snow remaining north of the area. The next area of uncertainty is regarding rain totals across the area; preliminary thinking is around 0.5 to 1.5 inch of rain, which will be narrowed down over the next few days. With the upper level low slow to move offshore, the next warm up further west is likely to struggle reaching the region, with highs early next week likely to remain in the 50s ahead of another possible rain event on Tuesday.

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