Jan 20, 2012: Snow Returns Tomorrow

After a weak clipper brought light snow amounts to Long Island and southern Connecticut last night, mostly sunny skies returned for today with temperatures reaching the lower 30s inland. Further east, however, temperatures unexpectedly peaked in the middle of the night in the mid to upper 30s in the immediate NYC area and the upper 30s in Long Island and southern CT, before dropping into the lower to mid 30s by the afternoon.

Cloud cover is starting to increase across the area, however, and for the first time since October, snow will fall tonight into tomorrow without changing over to rain for most places with the first significant snowstorm for the area of the winter months. Snow amounts will be nowhere near those observed with the storms last year, as this will be a weak and fast moving storm, although most of the area is expected to see at least 3 to 7 inches of snow, making this the 2nd significant snowstorm of the entire winter. The brief surge of cold and snow will not last for long, however, as a warm air mass will quickly move in, with temperatures in the 50s, rain and even some possible thunderstorms returning by Monday.

Tonight – Saturday: Moderate Snow

As mentioned with last night’s update, a slightly further south scenario appeared more likely, and the scenario I went with for yesterday’s update is very close to the final expectation with only a few minor changes in the forecast. The model guidance is also in an overall agreement for at least 3 to 6 inches of snow to fall across most of the area, accompanied by a changeover to sleet in parts of NYC, NE NJ and Long Island by the end of the storm.

Storm Scenario: The low pressure will stay suppressed, moving through West Virginia, into the Washington DC area and then off the coast of southern New Jersey. There is a high pressure to the north of the storm, and with plenty of cold air ahead of the storm, the entire NYC area, even down south to the Washington DC and Delaware/southern NJ areas, will start out with light snow. Throughout the event, warmer temperatures aloft at 850mb will steadily push further north, although the high pressure will help to keep surface temperatures colder, resulting in a more significant freezing rain events for parts of the central Mid Atlantic, including Maryland and southern Pennsylvania. These warmer temperatures will make their way into central NJ and PA, resulting in a changeover to sleet, although by then the storm will be nearing its end, and temperatures aloft may warm up just enough so that at the last hour or two of the storm, the precipitation type changes over to sleet for parts of northeastern NJ, NYC and Long Island. Any sleet, however, will not have significant impacts on the total accumulations for the NYC area since most of the snow will accumulate by the time that the precipitation changes over to sleet.

Forecast for NYC Area: The storm is moving quickly through the Great Lakes right now, with snow expected to start falling in the western parts of the area around 2-3 AM and in the eastern parts around 3-4 AM. Temperatures will be in the upper 10s inland, lower to mid 20s in the immediate NYC area and mid 20s in Long Island/S CT at the start of the storm, allowing the storm to start out with light snow. The snow will intensify throughout the early morning hours, with a widespread moderate snow expected to fall across the area between 6 and 11 AM. As observed in the Great Lakes region and with the short range models showing a slightly heavier band of snow moving through, a brief period of heavy snow may be possible especially in northern NJ/SE NY in the morning hours. With the heavier snow in the morning hours, temperatures are still expected to be in the lower 20s north and west of NYC, resulting in higher snow ratios. Temperatures will steadily warm through the late morning hours, with sleet starting to mix in parts of NE NJ, NYC and Long Island after 10-11 AM. The storm will end by 1-3 PM across the area with cloudy skies afterwards and high temperatures reaching the mid to upper 20s north and west of NYC and the upper 20s to lower 30s in NYC and Long Island.

Total Snow Forecast: This storm does not have a lot of moisture and will be fast moving, so significant snow amounts are not expected anywhere in the region, with any 8+ inch amounts expected to stay isolated at most. For the area, however, with at least 0.5 inch of QPF along with slightly higher liquid to snow ratios, at least 4 to 6 inches are expected to fall across northern NJ, SE NY and southern Connecticut, where the heaviest snow in the area is expected to fall. Slightly lower amounts of 3-5 inches can be expected in NYC and Long Island, where some sleet is expected to mix towards the end of the storm. Locally higher amounts of up to 7 inches may be possible in the northern parts of the area.

Across the region, changes in the snow map were minor for the southern half of the storm from yesterday’s map, only slightly extending the accumulations further south, although the 1-2 inch zone based on the latest reports is likely to extend down into Washington DC and southern NJ. More significant changes were made to the northern half of the storm, however, where it appears that less precipitation than previously expected will fall. As a result, the heaviest accumulations of about 5 to 7 inches will be placed from central/northern Pennsylvania into northern NJ, SE NY and into southern CT.

Possible Changes: Although this is the final forecast for the storm, minor changes sometimes take place with the forecast as the storm is ongoing. One potential concern for the storm is that some of the short range models have a dry slot for NYC, with the moderate snow not starting until the later morning hours while surrounding areas see moderate-heavy snow, in which case accumulations for NYC would be lowered and accumulations for locations surrounding NYC would remain the same. Another potential change would be if the storm is overall slightly drier than currently expected. Stay tuned for storm updates throughout the morning hours tomorrow.

Sunday – Next Week: Same Pattern Returns; Warmer Than Average Again

The snow event for tomorrow does not signal a pattern change; instead, the pattern is reversing back to the way it was before a large polar vortex dropped into central Canada a couple of days ago, with the strong cold retreating back to central/northern Canada, where it has been so far this winter. As a result, the pattern starting on Sunday will return to the storm track to the northwest of the area with occasional warmer temperatures returning. This reversal in the pattern has been mentioned throughout the last week, and although the magnitude of the warmth was overestimated at first, there were and still are clear signs that temperatures are likely to end up above average again next week.

After a chilly Sunday, with temperatures in the lower to mid 30s across most of the area, temperatures will steadily rise throughout the overnight hours as a large storm moves towards the Great Lakes region. There may be enough cold air initially that NW NJ and SE NY begin with light freezing rain, although temperatures will warm up later on, with any freezing rain changing over to rain. The warmest temperatures will take place on Monday, reaching the upper 40s to lower 50s across the area, possibly the mid 50s near NYC in the warmer case scenario. A strong cold front will move through, with showers and potentially even some thunderstorms for the afternoon and evening hours, followed by temperatures cooling down a little into the mid to upper 40s for Tuesday. Temperatures will remain mostly above average in the 40s through next week with another storm, more likely rain than snow at this time but still subject to change, by the end of next week.

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