Nov 20, 2013: Very Cold Sunday; Watching Thanksgiving

Forecast Highlights:

gfs_namer_102_850_temp_mslp_precipCold temperatures were observed across the area last night, with highs today again reaching the 40s. The cold air mass will quickly exit as temperatures rebound by the late week into the 50s, followed by scattered showers on Saturday and much colder temperatures, struggling to reach the mid-upper 30s for highs. A moderation is likely again by early-mid next week but with signals for a potential storm around the Thanksgiving time frame. (Image credit: NCEP MAG)

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Tuesday, November 19 Observations:

11.19.13As a colder air mass returned into the region, temperatures cooled down after the unseasonable warmth leading up to Monday; as the entrance of the cold lagged behind the front, temperatures peaked at 12 AM for most locations in the upper 40s to low 50s, with others reaching the same temperature or slightly exceeding it during the mid afternoon hours. Partly cloudy skies were generally observed, with a breezy NW wind at 15-25 mph. The highest temperature was 52 degrees in JFK Airport and New Haven, CT, and the coolest high temperature was 46 degrees in Montgomery, NY.



Today – Saturday: Warming Up, Saturday Showers

As a strong high pressure moved overhead through the region, clear skies and lighter winds allowed temperatures to fall into the mid 20s-low 30s for most, with temperatures as low as 18 degrees in Sussex, NJ and Montgomery, NY. Even though the coldest temperatures at the surface occurred this morning, however, the coldest temperatures aloft have already exited the region as the surface high pressure extends east of the area with weak ridging building over the region as heights lower over the western and central US. This will bring a somewhat warmer air mass for Thursday and Friday with temperatures warming back into the 50s.

With the high pressure overhead, mainly sunny skies are expected today with highs rising into the mid 40s for most of the area. Partly sunny skies are expected on Thursday with highs rising into the upper 40s to low 50s, with the trend continuing into Friday with highs in the low to mid 50s but with mostly cloudy skies as the next light rain event approaches the area. There was a significant variety in model solutions as of yesterday’s update; although today’s model runs are still not in agreement, they are much closer to an overall idea of a weak, developing wave of low pressure quickly moving through the northern Northeast/southeast Canada, bringing a cold front through on Saturday. As such, isolated to scattered showers are expected mainly on Friday night into Saturday morning/early afternoon, with rain totals generally below 0.1 to 0.2 inch, locally higher east of NYC.


Saturday Night – Tuesday: Much Colder, Windy; Flurries Possible

0z GFS 500mb heights and vorticity, showing a strong mid-upper level trough over the region, and the stalled upper level low in southern California that may affect the region by Thanksgiving (image credit: NCEP MAG).

gfs_namer_096_500_vort_htBehind Saturday’s cold front, despite producing little rain, the most significant cold outbreak of the fall is likely as cold arctic air that has been recently building up over western Canada will be able to spill southeast into the region with a strong 1050mb high pressure in the Midwest. Along with strong ridging in the northwest US north of a stalled upper level low in southern California, this will bring a strong trough into the region with 850mb temperatures near -12C to -16C, typical of an average wintertime cold surge. Much colder temperatures are expected on Sunday; although 24-hour high temperatures are likely to peak at midnight, daytime temperatures are expected to struggle rising into the low to mid 30s across the area, and for interior NW NJ/SE NY will likely fail to break 30 degrees. With a tight pressure gradient, windy conditions are also expected, with a strong NW wind at 15-30 mph sustained, likely gusting up to 40 mph. Partly cloudy skies are expected, with isolated snow showers possible on Saturday into Saturday night.

The coldest temperatures are expected overnight with clearing skies and decreasing winds, with lows in the 10s and 20s across the area. Temperatures at this time are likely to fall into the mid 10s towards interior NW NJ/SE NY, upper 10s to low 20s elsewhere in interior NJ and interior CT, low to mid 20s in the immediate north/west suburbs of NYC and Long Island, and mid to possibly upper 20s in NYC and the coast. With the continuation of the progressive flow, however, the coldest temperatures will be short lived as the high pressure shifts south and southeast of the area by Monday with an approaching weak low pressure from the Great Lakes leading to a quick moderation of the cold temperatures. Highs on Monday are still likely to peak only in the low to mid 30s inland and mid to upper 30s elsewhere, but with rising heights aloft as another trough digs over the north central US leading to warmer temperatures by Tuesday, reaching the low to mid 40s for highs. As the next section will discuss, this trough could play a significant role in the weather for Thanksgiving.


Wednesday – Beyond: Storm Potential Late Next Week

0z run of the ECMWF at hour 168, showing the potential setup by the middle of next week (image credit: PSU e-Wall).


The weather outlook becomes increasingly complex by late next week. A part of the trough currently entering the western US will split in the short range into a closed upper level low over southern California by this coming weekend, with ridging to its north supporting the downstream amplification of the weekend trough bringing the strong cold air mass. With ridging persisting over the northwestern US at least through early next week, another shortwave trough is likely to dig into the north central US by early next week, around the same time that the upper level low exits the southwestern US and tracks east towards the south central US, while ridging briefly holds over the western US likely supporting some amplification of the north central US trough before it begins to weaken ahead of another trough entering the NW US by the mid-late week.

The main uncertainty at this time is regarding the interaction between the southern and northern streams, including the timing and location of the interaction, whether the north stream can pick up the southern system up the coast and how much cold air will be available in the setup. Should the interaction occur as currently indicated, this would lead to a storm potential around Thanksgiving, likely towards next Wednesday or Thursday. The exact setup is still uncertain, and this morning’s model guidance, as should be expected in the 7-day range, remains inconsistent but continues to show the potential for a storm to affect the region. Given the overall progressive flow and lack of blocking downstream in the Atlantic, however, there is still some uncertainty regarding whether the storm develops and affects the region as opposed to staying weak and offshore, and should it affect the region, the pattern appears to support any snowstorm potential staying inland. Despite uncertainty with the storm, however, there is higher confidence of at least a transient cool down behind the storm with temperatures possibly back into 30s for highs by the end of next week. Stay tuned for more information over the next few days regarding the potential mid-late week storm and its impacts, if any, in the area.

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