Dec 23, 2013: Cold Returns, Snow Tomorrow

Forecast Highlights:

rad30The significant temperature contrasts that have been a common theme this winter continue once again, as following yesterday’s record warmth with 70+ degrees in NYC, temperatures will crash into the 30s on Tuesday and 20s on Wednesday, with an area of light-moderate snow possible near parts of the area on Tuesday evening that may lead to a white Christmas for some locations. A moderation in temperatures is then expected, but with a cold start to January likely across the region (Image credit: PSU e-Wall, NAM simulated radar for Tues evening).

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Sunday, December 22 Observations:

12.22.13Observations for Sunday may be described better as “May 22”, as temperatures on Sunday were unseasonably warm, more typical of late spring conditions, with widespread warm temperature records shattered across the region. As a low pressure tracked into Ohio and New York state, a very tight thermal gradient set up near a frontal boundary in the northern Northeast, separating the unseasonable warm air mass to the south from the frigid Canadian air to the north, where a major ice storm occurred. With the NYC area well inside the warm sector, as evidenced by record warm 850mb temperatures (1500m altitude) near 16.8C in Upton, NY, surface temperatures surged into the 60s across the area and even the low 70s in parts of NYC and northeast NJ, breaking records in all climate stations in the tri-state area. In Central Park, the high of 71 degrees far exceeded the previous record of 63, set in 1949 and 1998. Even more notable was the low of 61 degrees, which was the first day in recorded history (back to 1869) during meteorological winter that temperatures failed to fall below 60 degrees.

The highest temperature was 71 degrees in Central Park, NY and Newark, NJ, and the coolest high temperature was 60 degrees in multiple locations.




Tonight – Wednesday: Winter Returns With Cold, Some Snow

Earlier today, a wave of low pressure developed along the frontal boundary that has been gradually shifting east, removing the unseasonably warm air mass from the region. While rain persisted throughout the day, totals were lower than expected with heavy rain not as widespread as forecast, with 1/4 to 1/2 inch of rain for most of the area with locally higher totals. Continuing this year’s theme of frequent temperature swings, some of the cold air mass over Canada will spill into the region behind the front, bringing a quick return of winter-like conditions into the region.

While high temperatures on Tuesday are expected to peak at 12am in the mid 30s-low 40s for most of the area, daytime high temperatures will reach the low 30s inland and mid 30s elsewhere, with partly cloudy skies and a NW wind at 5-15 mph. With a strong shortwave trough moving through during the evening hours, mainly between 6-10pm, scattered snow showers are expected, with a narrow axis of moderate snow possible in parts of the area. Exactly where this sets up is uncertain, although at this time it appears it could set up over northern NJ, possibly extending into NYC, with a coating to 1/2 inch of snow possible or locally higher. Behind the light snow, temperatures will fall into the mid 10s in interior NW NJ/SE NY/CT, upper 10s to low 20s in the north/west suburbs of NYC, coastal CT and Long Island, and the mid 20s in NYC and the immediate coast. Mostly sunny skies are expected on Wednesday with highs in the mid-upper 20s.


Thursday – Beyond: Warmer Weekend; Cold Start to New Year Possible

The cold air mass will exit just as quickly as it came in, with moderating temperatures on Thursday rising into the upper 30s before a weak cold front moves through overnight, with most or all of the area remaining dry. Temperatures for Friday and Saturday are expected to reach the mid-upper 30s for highs with lows mostly in the mid-upper 20s. With a southwesterly flow likely returning on Sunday, another warm up in temperatures is expected with highs in the low-mid 40s possible.

Towards New Year’s Eve and into early January, the potential exists for a strong cold surge into the northeastern US, including the area. Some changes in the global upper level patterns are expected to occur by the end of the month, including a neutral-negative AO index as ridging in the northeast Pacific attempts to bridge across the north pole towards ridging present over Europe, with some southward displacement of the polar vortex over Canada towards the Hudson Bay or southeast Canada. The core of the cold in the northern hemisphere has generally set up over Canada this month with very cold temperatures, which has been seen earlier this month when some of the cold briefly spilled into the interior northeast with below average temperatures despite a lack of downstream blocking, very positive AO and a progressive flow. While a sustained cold pattern appears unlikely at this time, the potential is there for more significant cold to return into the region by the very end of the month into the start of January.

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