Mar 5, 2013: Rain, Snow, Wind For Weds-Friday

Forecast Highlights:

More sunshine was observed across the region today with lighter winds and warmer temperatures, peaking in the mid 40s to low 50s across the area. Cloud cover already began to increase across the region with precipitation spreading into the Mid Atlantic, however, as the most significant storm to affect the region since the early February blizzard continues to approach, with a long duration rain, snow, wind and coastal flooding event lasting through Friday.

 

 


Model Overview: Despite the storm not far from starting, the model guidance still has not settled on a single consensus, with a relatively minor spread that has larger implications on the forecast for the area. The GFS showed a significant nor’easter yesterday and was significantly north of the other models; since then it has trended south, and is now among the southern and drier models, hardly showing more than light rain/snow out of the coastal low on Wednesday night. Meanwhile, the NAM is now the northernmost and snowiest model, showing moderate to heavy snow bands reaching the NYC area with up to/over 6 inches of snow. The ECMWF has continued to gradually trend north, now supporting a long duration light-moderate precipitation event with at least light to moderate snow accumulations.

The main short term uncertainty at this time is how far north the heavy precipitation from the coastal low spreads. The GFS is likely too dry with its depiction of only light precipitation for most of New Jersey, with moderate snow accumulations likely to spread into at least central New Jersey but with increasing uncertainty further north into the area. The northern end of the heavy precipitation is close to the area, and minor north/south shifts will have a larger impact on the forecast for the area, ranging from just light rain/snow showers to several inches of heavy wet snow. Accounting for the uncertainty, I currently put 2-5 inches of snow in the forecast for most of the area excluding northwestern locations on Wednesday night, although additional revisions may be made to this range throughout the day on Wednesday. Should moderate-heavy snow bands expand into the area closer to what the NAM depicts, accumulations may need to be raised for the immediate NYC area and Long Island/S CT.

The next change to the forecast is the addition of a potential inverted trough on Thursday night into Friday morning. The interaction of the ULL and an area of vorticity in southern Canada has not been handled well so far, and today’s models trended towards an inverted trough in this time frame with a widespread area of light-moderate snow bands from north to south that add on to snow totals from earlier. North of the NYC area, this appears to be the main precipitation producer. There is still uncertainty regarding exactly where this feature sets up, how much snow falls with it and how cold/warm temperatures will be, although currently the focus of this appears to be north of NYC, with the potential for additional light to perhaps moderate snow accumulation for some areas. More information will be posted on this with storm updates tomorrow and on Thursday.

 

Regional Forecast: As the latest radar shows, precipitation is currently falling across Virginia and Maryland; most of it is generally snow. Heavy precipitation will continue to spread into that region, with heavy snow to continue in Maryland, interior Delaware, and south-central Pennsylvania/NJ through Wednesday evening, where moderate to significant snow accumulations are expected. Meanwhile, strong winds will develop for coastal areas, initially from the ENE/NE but later on switching to the north, with sustained winds of 25-35 mph and gusts up to 50 mph, locally higher, expected, along with coastal flooding throughout the Mid Atlantic coast into New Jersey and the NYC area.

As the low tracks off the coast and slows down, heavier precipitation will spread ENE towards the NYC area on Wednesday evening and night. As previously mentioned, there is some uncertainty regarding how far north the heavy precipitation extends over the NYC area, although widespread light to moderate snow, potentially heavy, will continue to spread into the NYC area. Later into the overnight hours into Thursday, moderate to heavy snow/rain will also spread into southern New England into Massachusetts, with moderate snow accumulations likely in that region as well. By Thursday night, a potential inverted trough may result in additional moderate snow accumulations towards western New England, the eastern half of NY state, and perhaps extending into NE PA and northern parts of the NYC area. The storm will finally end on Friday as the low departs the region with lighter winds and clearing skies.

 

Forecast For NYC Area: This is a tough forecast to make for the NYC area, and despite the storm not far from starting, there remain some uncertainties. Light rain/snow showers are expected to develop late on Wednesday morning into the early afternoon hours; initially, precipitation type may be mixed, although locations with heavier precipitation rates are likely to end up with snow with dynamic cooling. The peak of the coastal low will take place between the evening and the mid overnight hours, with increasing impacts from NW to SE. Light to moderate snow is expected across most of the area, with potential mixing with rain in parts of Long Island, with precipitation weakening towards the early morning hours. Currently, at least moderate snow is likely for the immediate NYC area, Long Island and S CT, although the potential is there for heavier snow rates, in which case accumulations may be higher than currently expected.

Occasional precipitation is expected on Thursday with mainly cloudy skies, with temperatures likely warming up enough for rain to mix with the snow showers, with little to no accumulations likely for most of the area. The next round of precipitation is likely on Thursday night into Friday morning. There is still some uncertainty with this part of the storm although at least additional light to moderate snow is possible north of NYC, with lighter precipitation further south. Precipitation is expected to end on Friday morning as skies gradually clear later in the day and temperatures warm up closer to average.

At this time, the forecast is for at least 2 to 6 inches of snow across the area from the coastal low pressure through Thursday, with the lowest accumulations further west and the highest accumulations east of NYC where amounts may be locally above 6 inches. This is generally expected to be wet snow, which may result in downed trees and power lines in locations that receive heavier snow accumulations. Additional light to moderate snow accumulations are possible on Thursday night as well, especially north of NYC. Windy conditions are expected as well, with a NE wind gradually turning north, sustained at 20-35 mph across the area with gusts in the 40-50 mph range for most, especially towards Long Island where gusts up to or locally above 50 mph are likely. Coastal flooding is also expected with a storm surge of 2-4 feet possible; this is a concern for coastal locations, especially those that have not fully recovered from Sandy. For more localized forecasts, please refer to the 5-Day Forecast page.

As previously mentioned, there is still uncertainty on some of the smaller details of the storm, specifically regarding how much snow falls across the area on Wednesday night, and a potential inverted trough on Thursday night that may enhance snow totals especially north of NYC. At this time, I sided a bit more conservative than the latest high resolution models, although the possibility is there for heavier snow bands to spread into the area, in which case forecast accumulations may be raised up to or over 6 inches for the immediate NYC area and further east. Storm updates will be occasionally posted throughout Wednesday and Thursday both here and on twitter.

 

Longer Range Update: A temporary warm up is expected for the weekend into early next week with more sunshine and highs returning into the 50s for parts of the area. This warm up is not expected to last long, however, as another storm is possible towards early-mid next week, with the potential for a near to slightly cooler than average pattern with blocking to return for the longer range.

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