Nov 16, 2011: Rain Tomorrow, Interior Snow?

Note: Today’s update is a short one, with a discussion focusing on tomorrow’s expected storm. Another brief update will be posted tomorrow; the next full update will be posted on Saturday. In addition, the winter outlook will be delayed until Wednesday, 11/23.


Tomorrow’s Outlook: Rain Expected; Snow Possible

Although the forecasting models usually nail down storms in the short range, in some cases there are weak storms that the models do not catch up to until the short range, and tomorrow is another one of these cases. The models have indicated for the last few days that a secondary wave of low pressure could form on Thursday, and I did mention on my update from Monday, when some models failed to show any secondary storm, that a wave of low pressure would develop but would do so on Wednesday night and stay offshore. It was not until yesterday that the models began showing more widespread precipitation affecting the area.

This is in the very short range, with less than 24 hours left until the event, but the models have been trending further west with the storm, with the SREF and GFS bringing light to moderate precipitation in the area. The NAM, although keeping most of the precipitation to the south and east of NYC, has trended further west and wetter as well, and if the latest trends are in fact correct, may end up even further west by its next run early tomorrow morning. The short range RUC model agrees with this trend as well, bringing precipitation as far west as eastern Pennsylvania. Exactly how far west the storm ends up is uncertain as this is a last minute change in the forecast, but it is likely that the majority of the area, if not the entire area see some precipitation out of this storm.

With the storm moving through the area at the same time that a strong trough moves in, the potential is there that not only rain falls out of this storm. With precipitation falling, colder air would be pulled closer to the surface, with temperatures below the 925mb layer ending up near to below freezing. Although not enough cold air is in place to support snow falling down to the sea level, meaning that NYC and its immediate surroundings would see light to moderate rain tomorrow, enough cold air is in place that should moderate precipitation fall tomorrow afternoon and evening as far west as northern NJ, snow would likely mix with the rain especially in the higher elevations of northern NJ, SE NY and Connecticut. The storm also means that high temperatures would end up colder than what most forecasts currently suggest; should the latest trend placing the precipitation over the area verify, temperatures would peak during the day in the lower to mid 40s from NYC and further west and in the mid to upper 40s in Long Island and southern Connecticut. The actual 24-hour highs would be at 12 AM as temperatures drop throughout the overnight hours as the cold front moves through.

Overall, light rain is expected to develop across the area again tomorrow morning, lasting through the evening hours, with occasionally moderate rain possible in NYC and Long Island. As colder air moves in, snow may mix with the rain in interior northern NJ and SE NY, although little to no accumulations are expected. The precipitation will end by tomorrow evening as skies clear and temperatures drop into the mid 20s to lower 30s across most of the area for lows. Stay tuned for a few short updates on this storm tomorrow afternoon.

Longer Range Forecast Overview:

– Cold temperatures continue on Friday with mostly sunny skies, peaking in the lower to mid 40s inland and the mid to upper 40s across the area. As a ridge rebuilds into the region again, mostly sunny skies will continue on Saturday with highs in the lower to mid 50s across the area.

– Sunday will bring partly cloudy skies with warmer temperatures, peaking in the upper 50s to lower 60s across the area, and a few mid 60s may be possible near and SW of NYC in the warmer case scenario. A cold front will move through overnight, bringing mostly cloudy skies and a few showers.

– Monday and Tuesday are expected to be mainly dry, with partly sunny skies and a transient trough producing near to slightly below average temps, with highs in the mid 40s to lower 50s across the area and lows in the upper 20s to upper 30s likely.

– There is more uncertainty afterwards, but some models suggest that a storm may be possible on Wednesday and Thursday of next week. The models are still having difficulties handling this time frame, however, so details may still change with this storm. The outlook for Thanksgiving will be discussed in more details on Saturday.

– Behind the potential Wednesday-Thursday storm, yet another ridge will build into the central and eastern US as the cold that has built up to that point in southern and central Canada is weakened by the strongly positive EPO, likely bringing drier conditions with warmer temperatures for the weekend.

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