Dec 27, 2013: Rain Sunday, Then Cold

Forecast Highlights:

nam-hires_namer_060_sim_reflectivityChilly temperatures will continue today, but with a brief warm up on Saturday into the upper 40s before a coastal low moves through on Sunday, producing widespread moderate to heavy rain with up to an inch expected. This system will then be followed by a very cold air mass as temperatures struggle to reach 30 degrees for highs through the majority of the week (Image credit: NCEP MAG).


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Thursday, December 26 Observations:

12.26.13Temperatures failed to drop much from Wednesday’s cold high temperatures, with a weak storm system spreading widespread light snow across the area, especially in northern NJ and SE NY, during the morning hours with up to a coating of snow for most locations. Some sunshine was observed later in the afternoon with high temperatures peaking in the low-mid 30s inland and the mid-upper 30s for most other locations except for eastern Long Island, which surpassed 40 degrees.

The highest temperature was 44 degrees in Montauk, NY, and the coolest high temperature was 31 degrees in Sussex and Andover, NJ.



Today – Sunday: Warming Up, Then Coastal Low Expected

Following the departure of yesterday’s weak system that produced areas of light snow in the morning, a transient cold air mass is moving through the region, which will keep today’s high temperatures in the 35-40 degree range for most of the area. By Saturday, however, the trough will depart with a surface high pressure extending south of the region, which along with a frontal boundary stalling near the Adirondacks into coastal Maine as a low pressure develops near the Great Lakes, will allow southwesterly winds to spread across the region with mostly sunny skies and temperatures in the mid to upper 40s throughout the area.

Wetter conditions will return for Sunday as a coastal low pressure is expected to develop and track up the coast as a strong shortwave currently over Texas will emerge out of the southern US and track up the East Coast, interacting with the northern stream shortwave reflected by the surface low over the Great Lakes but with the systems failing to phase while over the region. With the northern stream low pressure remaining northwest of the precipitation shield of the coastal low pressure, along with the lack of an antecedent cold air mass as the frontal boundary holds the cold air north of the Adirondacks into coastal Maine, there will not be enough cold available for the coastal low to produce widespread snow, with rain expected to be the main precipitation type across the majority of the region. Surface temperatures will not warm up to the full potential supported by the air mass, however, as after falling into the mid 20s-low 30s across the northeast US on Saturday night, cloud cover moving in will limit the warming of temperatures, with highs expected to peak towards the late morning-early afternoon hours before rain spreads in. Towards West Virginia, enough low level cold may be left over initially to support freezing rain, but with otherwise plain rain expected. As the low tracks towards New England, some colder air aloft will filter into the system to marginally support wet snow in northern NY state into central-northern New England, especially in Maine which will remain north of the frontal boundary with cold surface temperatures in the 10s-mid 20s, but with the NYC area expected to observe plain rain. High temperatures will depend on the timing of the system, as throughout the duration of the precipitation, temperatures are expected to range from the mid 30s away from the coast to the upper 30s-low 40s near the coast.

For the NYC area, mainly cloudy skies are expected with rain developing after at least 1-3pm and continuing through 12-2am, with highs peaking in the early afternoon in the upper 30s to low 40s across the area before falling into the 35-40 degree range throughout the duration of the rain. Heavy rain is likely at times especially over NYC and further south/east, with near/locally over an inch of rain expected while locations further inland are expected to observe at least 3/4 to 1 inch. With the low pressure likely to remain offshore, winds are not expected to be a significant issue, although breezy conditions are likely especially in eastern Long Island.

Next Week: Cold Start To New Year, Some Snow Possible

Temperatures will struggle to cool down much behind Sunday’s low pressure, falling into the low-mid 30s on Monday morning before rising into the upper 30s-low 40s by the afternoon with partly sunny skies and a breezy NW wind. Colder temperatures will begin to slowly enter the region with partly sunny skies on Tuesday and high temperatures only in the upper 20s inland and low 30s elsewhere. As the polar vortex is displaced into southeastern Canada, the frigid air mass will settle just north of the US/Canada border, with some of the cold air extending into the region to support at least moderately below average temperatures. For New Year’s Eve, mostly cloudy skies are expected with temperatures near 25 degrees, along with the risk of isolated snow showers later overnight or into Wednesday morning. Wednesday and/or Thursday are currently expected to be the coldest days, with high temperatures in the mid 20s likely and lows in the 10s across the area, possibly the upper single digits towards interior NW NJ/SE NY.

The next uncertainty in the outlook is towards late next week on Thursday and Friday when some of the model guidance suggests the next potential for a storm system affecting the region exists. The latest GFS runs are the most bullish with this potential, depicting a cutoff upper level low over northern Mexico emerging into the US and phasing with a northern stream shortwave over the central US to lead to a significant rain/snow storm affecting the region, while the CMC depicts a relatively weak low to the north of the area leading to some rain/snow, and the ECM keeps the region dry. Looking at the GFS ensemble members, representing the GFS model run multiple times initialized with slightly different conditions each time, most members depict some sort of a system affecting the region with snow and/or rain, but not to the extent of the 6z GFS run. Although the main players in this setup are at least 96-120 hours out (4-5 days) from reaching the western US coast, they are still over the poorly sampled Pacific Ocean which will likely lead to model difficulty in handling this potential system throughout the next few days. Given that the potential for precipitation exists in this time frame, the 8-day forecast to be updated later today will include a slight risk of rain/snow, although there is too much uncertainty in the smaller details at this time to go more in-depth into a high confidence outlook. The potential does exist for a more significant system to affect the region, however, which will continue to be tracked over the next few days.

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