Dec 22, 2013: Record Warmth Today, Cold Midweek

Forecast Highlights:

nam-hires_namer_018_sim_reflectivityAn unseasonably warm and moist air mass is currently placed over the region, with widespread record warmth as high temperatures surge well into the 60s for most of the area and low 70s in NYC. The record warmth will give way to a rapid crash in temperatures, however, as following heavy rain on Monday and highs in the 50s, another cold air mass will return for the midweek, with highs in the 30s on Tuesday with scattered snow showers and only in the 20s on Wednesday (Image credit: NCEP MAG)

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Saturday, December 21 Observations:

12.21.13The frontal boundary from Friday remained nearly stationary over the northern Northeast region, while a southwesterly flow continued over the area with an even warmer air mass making its way into the region with unseasonably warm 850mb temperatures over 10C. Mostly cloudy skies were generally observed but with some clearing in cloud cover by the mid-late afternoon, with high temperatures peaking in the mid 50s for most of the area and the upper 50s-low 60s over the immediate NYC area. Despite being unusually warm for December, the peak of the warmth had yet to be reached.

The highest temperature was 65 degrees in Central Park, NY, and the coolest high temperature was 52 degrees in New Haven, CT.



Today’s Storm Summary: Record Warmth

A major storm system affected the eastern half of the US over the last two days as a wave of low pressure developed in the central US along a stalled frontal boundary, rapidly tracking northeast into the region today while deepening. With a strong southwesterly flow aloft, an unseasonably warm and moist air mass entered the region, with temperatures at the 850mb layer (1500 meters height) at a spring-like 16.8C recorded in Upton, NY. While southwesterly winds kept coastal locations cooler, in the mid-upper 50s, the rest of the area surged well into the 60s and even the low 70s in NYC and northeast NJ, easily breaking record high temperatures previously in the low-mid 60s, while warmer temperatures in the mid 70s were found south of the area. All climate stations in the area – Central Park, LaGuardia, JFK, Bridgeport (CT), Islip (NY), and Newark (NJ) – set record high temperatures today. Today’s high of 71 degrees in Central Park was among the warmest on record for December, but fell short of the all-time record of 75 set on 12/7/1998. The last time it was this warm in the second half of December was in 1984, with a high of 70 on December 29. Even more anomalous was Central Park’s low temperature of 61 degrees; not only did this break the record for the highest December minimum temperature on record, but it marks the first day in recorded history, going back to 1869, that temperatures during meteorological winter failed to fall below 60 degrees.

Last night’s regional radar from 2am (7z), depicting the severe weather in Ohio, ice storm in Maine, and major snowstorm to the north (Image credit: PSU e-Wall).

12.22_0700The record warmth was only one of multiple notable aspects of this storm. Since late November, a frigid air mass has been present over Canada, spilling at times into the region which along with the progressive pattern resulted in frequent temperature fluctuations, a recurring theme of this year’s winter pattern. A very strong thermal gradient set up near the stationary frontal boundary over the central Northeast, separating the very cold air mass to the north from the unseasonable warmth to the south. For example, Albany, NY, which was near the frontal boundary, was forecast to reach the 60s for highs, but remained near 32 degrees for most of the day; as the frontal boundary briefly shifted north, temperatures spiked to 52 degrees in less than an hour, then fell back just as quickly to 39 degrees. Even colder temperatures were found further north over northern New England, but with temperatures aloft above freezing, this resulted in a significant ice storm over northern NY state into VT/NH and Maine, where near to over an inch of freezing rain was reported leading to widespread damage and power outages, with nearly a foot of snow to the north. As the low pressure was in its developing stages yesterday, it produced a widespread severe weather outbreak in the southern US into the Ohio Valley, with widespread wind damage across a large coverage area and a few tornado reports in Arkansas.


Tonight – Monday: Warmth Continues, Heavy Rain Tomorrow

radsfcus_exp_newThe latest surface analysis and US radar from WPC posted to the left shows a 1007 mb low pressure centered near western NY state, with a cold front extending southward with heavy rainfall over the southeastern US. As the frontal boundary slowly shifts east, a wave of low pressure will develop tonight over the southeastern US and track near the area on Monday, bringing an additional surge of moisture into the region with high precipitable water content over 1.5 inches supporting a risk of heavy rainfall. This wave of low pressure was poorly forecast, originally indicated to remain mostly offshore with scattered showers brushing the area, although yesterday’s update noted the potential for more rainfall than forecast. Steady moderate rain is expected to develop late tonight, falling heavily at times mainly near and south/east of NYC, starting to end from west to east between 3-6pm. Rain totals of at least 1/2 to 1 inch are expected over northern NJ and SE NY, 1 inch near NYC, and 1 to 1.5 inch over Long Island and Connecticut.

Regarding temperatures, the model guidance has not handled the current unseasonable warmth well, especially the NAM which failed to depict temperatures rising overnight last night and kept most of the area below 60 degrees today. With a continued southwesterly flow and widespread cloud cover, along with the warm air mass persisting overhead, only a slight drop in temperatures is anticipated, with temperatures on Monday morning likely in the low-mid 50s inland, upper 50s to near 60 in NYC and northeast NJ, and the mid 50s in Long Island/CT. Temperatures will steadily fall by the afternoon and evening, reaching the 40s across the area by 7pm.


Tuesday – Beyond: Temperature Swings Continue with Cold Midweek

As previously noted, frequent temperature swings have been a common theme of this winter’s pattern with the abundance of cold air over Canada and a generally progressive flow over North America with a lack of blocking downstream, a pattern which is generally likely to continue through the rest of the month but with some changes possible later into January, which will be discussed in more detail by the end of the month with the updated winter outlook. This time frame will be no exception, as behind the early week frontal boundary sliding offshore, some of the cold Canadian air mass will spill into the region, leading to strong cold air advection with 850mb temperatures falling sharply to nearly -15C, bringing a return to much more winter-like conditions barely 2-3 days after May-like warmth.

Temperatures on Tuesday will fail to rise much from the morning lows, only peaking in the low to mid 30s across the area, with the possibility of scattered evening snow showers; at this time, it appears the potential exists across the area, but with the highest likelihood mainly west of NYC. The coldest temperatures are expected overnight, falling into the mid-upper 10s for interior locations, upper 10s-low 20s in the north/west suburbs of NYC, southern CT and most of Long Island, and mid 20s for NYC and the coast. Mostly sunny skies are expected for Wednesday with highs in the mid-upper 20s inland and upper 20s for the rest of the area, a major cool down from temperatures in the 70s only 3 days earlier.

As the trough quickly moves out with rising heights aloft ahead of the next approaching trough, highs will quickly rebound into the upper 30s-low 40s on Thursday with more widespread cloud cover by the afternoon hours and overnight hours as a mid level shortwave moves through but with little to no precipitation expected. Slightly cooler temperatures will return for Friday into the weekend, with highs in the mid-upper 30s and lows in the mid-upper 20s for most locations. Uncertainty increases beyond the weekend, but with the longer range model guidance indicating the potential for more significant cold towards New Year’s Eve or beyond.

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