After record warmth last weekend with highs near 71 degrees in NYC, a quick return to winter has followed with temperatures yesterday peaking in the upper 30s-low 40s with evening snow squalls that accumulated up to an inch, locally as high as 1.6″ in Islip, NY. Cold temperatures will return for today, followed by a temporary warm up for the late week and the weekend, only to be followed by much more significant cold to start January.
Today – Sunday: Cold Today, Warmer Weekend
A broad high pressure is currently covering the region, which along with a cold air mass overhead will provide the area with cold and mostly sunny conditions, as high temperatures rise into the mid-upper 20s inland and the upper 20s-low 30s for the immediate NYC area and Long Island. As the high pressure shifts east tonight with a southerly wind and increasing cloud cover, however, temperatures will fail to drop much, if at all from NYC and further north/west, and are expected to rise over Long Island and coastal CT into the 35-40 degree range by Thursday morning. A few isolated rain/snow showers can’t be ruled out, especially over CT. Mostly cloudy skies will continue into Thursday with highs in the upper 30s to low 40s.
With another trough passing through the region, colder temperatures will briefly return on Friday, with partly sunny skies and highs in the low-mid 30s for interior areas (NW NJ, SE NY) and the mid-upper 30s elsewhere. By Saturday, as the surface high pressure slides south of the area with a developing low pressure over the northern Great Lakes region, a broad southwesterly flow will resume across the region with another warm air mass advecting into the region, bringing a brief return of above average temperatures. Mostly sunny skies are expected on Saturday with highs in the mid-upper 40s across the area, although overnight lows are still expected to fall into the mid-upper 20s for interior areas and the low 30s in the north/west suburbs of NYC and coastal CT. Sunday’s outlook is more uncertain regarding the interaction of a developing coastal low pressure off the coast with the north stream, with the latest 6z GFS run the most aggressive in bringing moderate precipitation onshore. Due to the warm air mass already overhead and the presence of a low pressure well to the north/west, keeping the cold air trapped well to the north, should a storm track far west enough to affect the area, rain would be the favored precipitation type. The extent of precipitation will also determine high temperatures, as a further offshore system would support highs near the low 50s, while a further west system would keep high temperatures in the 40s. At this time, I am siding with the low staying just off the coast, with mostly cloudy skies and a slight chance of showers in Long Island, although this outlook is subject to some changes over the next few days.
Monday – Beyond: Much Colder, Long Range Storm Potential
The main highlight in the longer range is the cold expected to return by the end of the year and the start of 2014. With above normal heights near the polar regions, supporting a fall in the AO index towards negative, and more frequent ridging in the western US, the polar vortex over Canada that has sustained very cold temperatures for the majority of the month will be displaced further south, towards the Hudson Bay and southeast Canada. This is expected to bring below average temperatures back into the region starting early next week, with colder temperatures likely to continue overall through the first 1 or 2 weeks of January.
Monday’s temperature outlook depends on how fast the cold air surges into the region, as strong cold air advection will likely prevent temperatures from significant rising during the day. I am currently siding with a slower entrance of the cold with highs in the low-mid 30s for most of the area, although this is subject to slight changes. Colder temperatures will return overnight with lows falling into the 10s for most of the area, with Tuesday likely to observe partly sunny skies and highs in the mid 20s-low 30s range. There have been some hints at a potential clipper system moving through the region for New Year’s Eve, producing widespread light snow; this is still an uncertain potential, and for now I kept the outlook dry on Tuesday night with continued cold temperatures in the mid 10s-low 20s for lows, including low 20s in NYC, although this potential will be watched over the next few days.
With polar vortex displaced further south and with a frigid air mass sitting just north of the region, temperatures are expected to be colder than average to start the new year, but with the coldest temperatures still remaining well to the north. The main uncertainty is towards the second half of the first week of January, with the potential for a storm to affect the region sometime during the January 3-7 time frame. As this is over a week away, specific details cannot be determined this far out, but any organized system in this time frame would be capable of producing frozen precipitation in parts of the region and potentially dragging some of the frigid temperatures in southeast Canada into the region, which could lead to much colder than average temperatures. More information will be posted on the early January outlook over the next few days.
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Tuesday, December 24 Observations:
With a cold air mass quickly returning into the region, temperatures peaked in the upper 30s-low 40s across the area, much colder than the upper 60s-low 70s observed on Sunday. Partly to mostly cloudy skies were observed, increasing by the evening as heavy snow squalls affected parts of the area. The first area was over far northern NJ, with up to 1/2 inch of snow reported in a short period of time. The second area was over interior SE NY into Fairfield and west-central Suffolk counties, where heavy snow was observed during the evening hours with up to an inch of snow recorded. The highest total found was 1.6″ in Islip, NY, with snow rates of near 3″/hour observed under the snow squall.
The highest temperature was 43 degrees in Newark, NJ and JFK airport, NY, and the coolest high temperature was 36 degrees in Montgomery, NY and Sussex, NJ.