Nov 23, 2012: Light Rain/Snow Likely Tuesday

Forecast Highlights:

The stable pattern with little variation in temperatures that has been in place since last Tuesday is coming to an end with a cold front moving through the region tonight, producing scattered showers north of NYC with much colder temperatures for this weekend. A stormy pattern is unlikely to develop through the start of December, although a weak storm will affect the region during the middle of this week with light rain and snow likely.




Weekend Outlook: Cold, Windy

A strong cold front will move through the region tonight, bringing scattered showers to the Northeast US mostly north of NYC and ending the pattern that has been in place since early last week with little variation in temperatures. However, there will not be much rain with the cold front yet; most of the area is only 25-50% of the average November rainfall, and as will be mentioned in the next sections, there is no sign of the dry pattern ending through at least the start of December.

Behind the cold front, partly cloudy skies are expected for Saturday with stronger winds from the NW, gusting up to 30-40 mph. Much colder temperatures are expected, only peaking in the upper 30s to lower 40s for interior north/western areas and the low to mid 40s for the rest of the area. Lake effect snows are expected for the western Northeast, although no precipitation is expected for the area other than the potential for flurries towards NW NJ and Orange county, NY.

Colder temperatures are expected for Saturday night with partly cloudy skies, dropping to the low 20s inland and the mid to upper 20s for the rest of the area, with NYC and the immediate coast near the low 30s. Sunday will still be chilly but at least a degree or two warmer than Saturday, with weaker but still breezy winds expected out of the west.

Next Week: Chilly; Storm Expected Mid Week

Chilly temperatures will continue into Monday but slightly warming up, reaching the low to mid 40s inland and the mid to upper 40s for the rest of the area. Meanwhile, a progressive shortwave will race east through the central and eastern US, with a weak low pressure expected to develop near the south central US, quickly moving into the region on Tuesday and Tuesday night. The model spread has narrowed down since last night but uncertainty continues in the forecast; the ECM model remains consistently suppressed with barely any storm evident, while the GFS and CMC have shifted considerably south and weaker but still show at least a weak storm affecting the area with light snow especially from NYC and further west. Despite a developing east based -NAO, the pattern remains progressive over the US, and an amplified strong storm well west of the area is unlikely at this time. There is still uncertainty regarding the shortwave, however, considering it is still over the Pacific Ocean and isn’t expected to move into the US until Sunday, when it will be sampled better, and until that happens the model guidance will likely continue to remain somewhat inconsistent between runs.

A likely range for the possible track of the storm at this time is between at least North Carolina/southern Virginia and the northern Mid Atlantic or southern Northeast (as in NYC or southern New York state). Both tracks will likely result in at least some precipitation for the area, although the track and intensity of the storm will determine the intensity of the precipitation as well as where snow falls and how much. As this will not be a very moist storm, no significant snow amounts are expected, although the potential is there for a swath of light to potentially moderate snow to affect parts of the region north of the storm track as long as the low isn’t too weak and suppressed. Should the storm take a track supportive of snow in the area, the best chance of would likely be from at least NYC and further north/west, although it is still a bit too early to know with enough confidence exactly where it snows and how much. Based on recent trends, I am siding closer to the northern runs from today with the potential for accumulating snow in the northern Mid Atlantic and the southern/central Northeast, closer to or a bit north of today’s 12z GFS run, but not as far south as the ECM, although this is still subject to change; the potential is still there that the low ends up stronger and more north with future runs, especially with the ECM. Stay tuned for more information on this storm over the next few days.

Longer Range: Cold, Then Warmer

Although the model guidance differs with the handling of the mid week storm, there is a better consensus for a stronger cold air mass for late in the week behind the storm, with temperatures similar to those of this weekend, if not a bit colder. By next weekend, although a -NAO and -AO pattern will remain in place as ridging persists near Greenland and the Arctic Ocean, the Pacific pattern remains unfavorable for sustained cold in the US, with rising 500mb heights expected across the US. With this development, the pattern for the first week of December is likely to end up near to warmer than average for the region with no strong cold air masses expected, with not many significant storms likely through the first few days of the month as well. Unlike last year, however, there is actual blocking near Greenland with the -NAO expected to persist, and the potential is there for the pattern to trend colder towards the middle of December. Stay tuned for more information on the longer range with the winter outlook, to be posted on Tuesday.

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