Dec 17, 2011: Much Colder Temperatures For Sunday

As a trough moved into the region today, mostly cloudy skies were observed with colder high temperatures, reaching the upper 30s to lower 40s inland and the lower to mid 40s across the rest of the area. Scattered flurries were even observed in parts of the area. As a colder air mass moves in, much colder temperatures are expected tonight, with the coldest temperatures so far this winter possible, with much colder high temperatures expected for tomorrow. This cool down will be brief, with warmer temperatures returning next week along with more rain for the mid week, mixing with light snow in the interior parts of the area at the start of the storm, before colder temperatures return again towards the end of next week into the weekend.


Tomorrow's Outlook:

The model guidance has been underestimating the intensity of the cold air mass for the last few days, as the models have been gradually trending colder for tomorrow's highs, a trend which is still continued with tonight's 00z NAM run, which interestingly keeps almost the entire area below freezing for high temperatures, with temperatures failing to reach 30 degrees north and west of NYC. The NAM and GFS typically have a slight cold bias when it comes to high temperatures during cold spells, so while widespread below freezing high temperatures are not expected at this time, Sunday will end up much colder than previously expected.

With mostly to partly cloudy skies tonight, temperatures will steadily drop across the area, reaching the mid to upper 10s inland, upper 10s to mid 20s across NE NJ, SE NY and southern CT, lower to upper 20s in Long Island, and upper 20s to lower 30s in NYC. With mostly to partly sunny skies on Sunday, much colder high temperatures are expected, reaching the upper 20s inland and the lower to mid 30s across the rest of the area.


Monday - Thursday: Warmer, Rain; Some Interior Snow

With the trough quickly moving out, Monday will bring warmer temperatures once again, reaching the lower to mid 40s inland and the mid 40s across the rest of the area, potentially reaching the upper 40s near and southwest of NYC, along with mostly sunny skies. Clouds will increase on Monday night as a cold front approaches the area, stalling nearby on Tuesday while bringing mostly cloudy skies with the risk of isolated showers, potentially mixing with light flurries towards NW NJ/Orange County. Temperatures will be colder as well, peaking in the upper 30s to lower 40s inland and the lower to mid 40s across the rest of the area.

There is no high pressure to hold the cold air mass in place as the next storm approaches for Wednesday and Wednesday night, and a warm air mass will move into the area to bring rain for the main part of the storm. Despite the warmer air mass moving in, the potential is there for precipitation to move into the area on Tuesday night while parts of the cold air mass are still left. Although the air mass is not very cold, it will be cold enough to bring the potential for a rain/snow mix in the interior parts of the area, especially in northern NJ, SE NY and southern Connecticut, although very little, if any accumulations are expected from any wintry mix. Wednesday will bring warmer temperatures, reaching the mid 40s inland and the upper 40s across the rest of the area, along with occasional showers. These showers will continue through Wednesday night with temperatures staying steady at first before slightly dropping. Drier conditions will return for Thursday afternoon and evening with high temperatures ending up similar to, if not slightly warmer than those of Wednesday.


Longer Range: Searching For Snow

The pattern recently has been unusually mild compared to what is typically observed during December; since December 1, the entire East Coast is covered with warmer than average temperatures. NYC has been approximately 5 degrees warmer than average, with parts of the Northeast seeing much higher departures. This is a result of the current pattern which is unfavorable for cold and snow in the East, with a +NAO, +AO, a lack of blocking near Greenland, and a cold stratosphere. There continue to be no signs of any significant stratospheric warming event throughout the long range, and while there will be minor changes with the pattern from time to time, at least through early to potentially mid January, no pattern flip is expected where the East sees a more consistently colder and snowier pattern.

Although the pattern is unfavorable for snowstorms, it does not mean that snow is impossible in the region, especially if the timing and locations of storms are supportive. As I mentioned with my update last night, although snow is not impossible in the NYC area, anything more than light snow is unlikely under this pattern. There have been times when snowstorm happened with unfavorable patterns, such as late February and late March this year, but many parts of the set up have to end up in the right places for such a scenario to happen.

Since the models changed some parts of the Wednesday storm, parts of the outlook have changed for the late week into next weekend. Increased clouds are likely on Friday with the potential for some showers, before colder temperatures potentially return for the weekend. Yesterday, it was mentioned that there could be a storm potential over the weekend, but due to the changes in the timing, this potential was moved to Friday into early Saturday. Looking forward into the time frame after Christmas, however, the first potential for a snow event could be possible for the area. The pattern is still unfavorable, and a significant snowstorm is very unlikely, but if any low pressure in the time frame ends up in the right location with supportive timing, a snow event could be possible for parts of the region, potentially including the area, although the Northeast would still have a higher probability than the Mid Atlantic of seeing a more significant snowstorm. This potential is still highly uncertain, and especially given the unfavorable pattern, it is possible that this potential may fail to materialize and the area sees a mild rain again. Stay tuned for more information on the longer range.