Nov 26, 2012: Tuesday Rain/Snow, Then Cold Again

Forecast Highlights:

After warmer temperatures for the area today, cloud cover will be on the increase tonight as a fast moving low pressure approaches, producing the second snow event for the month mostly focusing west and southwest of NYC. Behind this storm, temperatures will cool down for the second half of the week, but will not last for long as a warmer pattern develops for the first week of December, possibly beyond.

---

Update: The winter outlook is now set to be posted on Wednesday, November 28.


Tuesday: Light Rain/Snow Expected

The second snow event of the month is set to affect the region tomorrow, with widespread light snow accumulations especially west and SW of NYC. While this won't be a significant snowstorm or even a moderate snowstorm for most, it will only be an addition to what is already one of the snowiest Novembers on record due to the early month storm.

This will be a weak and progressive storm, with a well defined low pressure center only forming once the storm is offshore, at which point the coastal low will intensify while moving away from the region. Light snow is expected to spread into the region late tonight into Tuesday morning, with the heaviest precipitation expected during the afternoon hours. Surface temperatures will be marginal for snow further south and east, with NYC and Long Island expected to see rain for at least part of, if not the majority of the storm. The precipitation type is expected to be mostly, if not entirely snow west, SW and north of NYC. The snow will weaken by the evening as the coastal low begins to intensify overnight, moving away from the region.

At this time, a widespread area of light snow accumulations is expected from West Virginia to Pennsylvania, central/northern New Jersey, into SE NY and southern New England. The largest snow totals out of this storm are expected over SE Pennsylvania into parts of central NJ, where the heavier precipitation totals are expected. In this area, 3 or more inches of snow are expected, perhaps locally up to 4-6", but with these higher totals staying isolated rather than widespread. For the NYC area, at least 1 to 3 inches of snow are expected west and SW of NYC, with light accumulations up to or less than 1 inch possible in NYC and western Long Island. Amounts near 1 inch, potentially up to 2 inches for some, are expected for southern New England.

The main uncertainty at this time is regarding the northern end of the precipitation shield and the development of the coastal low. The precipitation shield has been trending north with today's runs, and for now I kept it a bit south of the latest models, although it's possible to see flurries north of the end of the light snow zone. Regarding the coastal low, this afternoon and evening's model runs, especially the GFS and RGEM, have trended more aggressive with the development of the coastal low, which although still remaining relatively insignificant for most of the region, manages to add totals for southeastern New England and potentially the immediate NYC area as well, depending on whether surface temperatures are cold enough and precipitation rates are heavy enough. An update will be posted tomorrow morning to reflect any necessary changes to the forecast.


Beyond the storm: Colder, then warmer pattern returns

Colder temperatures are expected to return behind the storm for the rest of the week. The coldest temperatures are expected from Tuesday night through Thursday, with overnight lows in the 20s for most of the area, dropping into the lower 20s for interior northern and western areas and perhaps slightly below 20 degrees for the higher elevations. Daytime highs are generally expected to be in the upper 30s to low 40s on Wednesday and Thursday, slightly warming up on Friday.

By Friday and next weekend, changes will be taking place in the pattern, but will not be favorable for cold and snow. The blocking pattern that has been mentioned with the recent pattern outlook is currently developing, but is set up far from the ideal position required to bring a cold and snowy pattern into the US, with the ridging in Greenland expected to remain east based while lower 500mb heights persist over the Gulf of Alaska into the western US, as shown to the left with the latest GEFS outlook from the PSU e-Wall. A mild air mass is expected to cover most of the US by the late weekend and early next week as the cold retreats back into Canada, with a ridge building across the eastern half of the US, providing warmer temperatures across the region with 50+ degrees likely to return. While the warmest temperatures are not expected to be long lived, with a warm storm likely around 12/5-6 accompanied by a cold front, there appears to be no significant outbreak of cold air into the US through at least the 2nd week of December. More information on the longer range will be posted with the winter outlook on Wednesday.