Dec 28, 2013: Coastal Low, Heavy Rain Tomorrow

[notice]New 12/28: A probability of precipitation table has been added to the blog.[/notice]

Forecast Highlights:

nam-hires_namer_039_sim_reflectivityA brief warm up is on the way for today as temperatures surge into the upper 40s for most locations and low 50s near NYC with mostly sunny skies. This warmth will be very short lived as a coastal low tracks up the coast, producing widespread heavy rain around or over an inch. Cold temperatures will be followed starting on Monday, with highs mostly in the upper 20s-low 30s through Thursday with the potential for late week snow.


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Friday, December 27 Observations:

12.27.13Behind Thursday’s light precipitation event, a transient cold air mass quickly moved through the area, with partly sunny skies but with temperatures slightly warming up compared with Thursday, peaking in the upper 30s to low 40s across the area. The cold air mass already exited by the overnight hours, with temperatures failing to drop much after the daytime highs especially closer to NYC and the coast.

The highest temperature was 42 degrees in multiple locations, and the coolest high temperature was 36 degrees in Sussex, NJ.



Today – Sunday: Warm, Then Rainy

Following the departure of yesterday’s trough, a northern stream shortwave will enter the north central US with a surface low pressure developing over the northern Great Lakes, while a frontal boundary extending eastward will nearly stall over the northern Adirondacks into coastal Maine. This will allow for a southwesterly flow to spread across the region today with a high pressure positioned to the south, with mostly sunny skies and highs in the upper 40s for most locations and the low 50s near NYC and NE NJ.

This setup will lead to a coastal system tomorrow which will track up the coast and produce widespread heavy rain. Another shortwave currently over Texas will eject out of the southern US and track up the east coast as a surface low pressure forms along the coast, interacting with the northern stream but failing to phase while over the region. With the cold air bottled up north of the frontal boundary over northern New England, no cold air will be in place to allow for a widespread snowstorm, instead supporting moderate to heavy rain across most of the region with temperatures ranging from the mid 30s inland to the low 40s along the coast. As the low tracks into New England, however, more cold air will filter into the system, resulting in heavy wet snow developing over northern NY, VT and NH, and a colder snowstorm over Maine which will remain under a cold Canadian air mass in the lower levels.

For the NYC area, high temperatures are expected to peak around noon in the mid-upper 30s inland, upper 30s-low 40s in NYC, coastal CT and the north/west suburbs, and the low-mid 40s in Long Island. Temperatures will hold steady or slightly fall as rain begins to fall after at least 12-1pm, becoming heavy at times towards 3-7pm. Rain is expected to taper off from SW to NE between 10pm-12am. With the low tracking near the coast, the strongest winds will remain offshore, although breezy winds up to 10-20 mph sustained from the NE are possible in eastern Long Island. Rain totals of at least 3/4″ to 1″ are expected for NW NJ and SE NY, and 1″ to 1.5″ for the rest of the area.


Next Week: Cold Returns, Late Week Storm Possible

As Sunday’s storm system departs the region, some changes will take place in the upper level pattern as the polar vortex stationed over central-northern Canada will be displaced into the Hudson Bay and southeast Canada, dragging the frigid temperatures over Canada closer to the US/Canada border. The vortex is expected to fail to spill over into the region, which will keep the coldest temperatures to the north, although at least moderately below average temperatures are expected for the majority of next week.

Colder temperatures will start on Monday as strong cold air advection prevents temperatures from warming up much from the morning temperatures, peaking in the mid to upper 30s before falling into the 20s and 10s overnight with a breezy NW wind at 10-20 mph. Tuesday and Wednesday are expected to have partly sunny skies with high temperatures in the mid-upper 20s for interior locations and the upper 20s-low 30s for the rest of the area. For New Year’s Eve, mostly cloudy skies and temperatures near 25 degrees are expected in Times Square, with low temperatures across rest of the area ranging from the mid 10s for interior areas to the low 20s in the north/west suburbs of NYC and the coast. A few scattered snow showers are possible on Wednesday.

More uncertainty returns for Thursday, however, as some of the model guidance suggests the potential for a more significant storm system to affect the region. Yesterday’s GFS runs were especially bullish in showing a significant snowstorm, although this morning’s GFS runs have backed down to some light snow, while the CMC shows snow showers and the ECM keeps the snow south of the area, although this is the first recent ECM run to depict the storm scenario. The two main players in this time frame are a southern stream ULL currently over northern California, which is expected to dig into Mexico before tracking northeast by the mid week, while the second system is a northern stream shortwave which as of now is still over the northern Pacific, a region where a lack of sampling can lead to difficulty for the model guidance to correctly handle the system, and is expected to enter the NW US by Tuesday, at least 96 hours away. While there is too much uncertainty at this range to forecast the specific details with high confidence, snow appears likely at this time frame, which has been included in the 8-day outlook with 60% probability of precipitation, and based on the upper level setup, should typical model biases be at play, the potential exists for a significant system in this time frame, which will continue to be monitored over the next few days.

2 thoughts on “Dec 28, 2013: Coastal Low, Heavy Rain Tomorrow

    • NYC Area Weather Post authorReply

      While probability is increasing for snow affecting the area, accumulations are still uncertain at this time. The potential exists for at least light-moderate accumulations, although should a more significant storm verify, such totals may be possible at least for parts of the region.

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