Dec 8, 2013 Storm Updates

[notice]The 8-day forecast has been updated as of 10:45 PM.[/notice]

Occasional updates will be posted below on the snow, sleet, ice and rain event affecting the area tonight into tomorrow. The next full forecast update will be posted on Monday.

Final storm precipitation totals in NYC:

Central Park – 0.38″
LaGuardia – 0.36″
JFK Airport – 0.28″

Blog Updates: (Regional radar from the Pennsylvania State University e-Wall)


6:55 AM: Freezing Rain To Gradually Turn To Rain, Taper Off

12.9_1130Throughout most of last night, the steady moderate to heavy precipitation remained to the south, towards central NJ into the Mid Atlantic, but as surface temperatures remained near to slightly below freezing, most of the area observed steady light freezing drizzle/showers overnight into the early morning, only recently changing to plain rain in the north/west suburbs of NYC. No reports of ice have been published yet by the National Weather Service, although airport observations show at least 0.05 to 0.10 inch of precipitation having fallen as freezing rain north/west of NYC.

As temperatures continue to slowly warm up, the area will change over to rain extending further inland from 7-10am, with scattered showers expected through the late morning to early afternoon. For locations that observed accumulating freezing rain, hazardous road conditions are expected this morning.


10:10 PM: Dry Evening, Then Sleet/Freezing Rain

12.9_0245After the previous update, light to moderate snow continued to fall over the area through at least 6 PM. Most reports are generally below an inch of snow, although there have been isolated reports of over 1 inch in parts of Long Island and central NJ. After the initial round of snow, however, precipitation significantly dried up across the region, and the latest radar posted to the left shows the region dry except for the next round currently in Virginia. This much drying has not been anticipated, and reflects the relatively poor short range forecasting of the storm as was seen earlier today with significant snow totals south of the area, with Philadelphia recording more snow this afternoon (8.6″) than during the entire winter of 2012-13.

Cold temperatures continue to hold on near the surface, near the 20s, but with mid level temperatures beginning to warm up and approaching freezing, with freezing rain a concern for most locations away from NYC and the coast tonight leading to ice accumulations. As such, when precipitation redevelops within the next few hours after 12 AM, northern parts of the area may begin with light snow, but otherwise with light rain expected from NYC and further east and light sleet/freezing rain north and west of NYC and into southern CT away from the immediate coast. Temperatures will be slow to warm up overnight, and light freezing rain is expected to continue into the interior north/west suburbs of NYC and towards NW NJ/SE NY through the morning hours, with hazardous road conditions likely with at least 0.10″ or possibly more of freezing rain likely. By the mid-late morning hours, a changeover to plain rain is anticipated as temperatures at the surface warm above freezing and into the upper 30s to low 40s for most.

Forecast Update: Some of the latest model runs have been suggesting the possibility of a stronger wave of low pressure on Tuesday behind the departing frontal boundary, with the NAM and GFS highlighting the potential for light to moderate snow, especially near and south/east of NYC. Currently, this does not have support from the other models, with the UKMET the closest and still decently south of the GFS/NAM with light snow showers east and south of NYC. At this time, I introduced 60-70% of light snow, mainly from NYC and further south/east in the 8-day forecast, with the possibility of 1-3 inches of snow. This is still a low confidence forecast at this time, however, and more information will be posted on this possibility on Monday morning.


3:50 PM: Snow Moving Into Area

nerad25Throughout the last few hours, heavy snow fell across Maryland, southern PA and southern NJ, significantly exceeding forecasts with accumulations up to 5-10 inches recorded. The heavy banding turned out to stay south of the area; as such, forecast snow totals remain close to the previous outlook. Snow will move in over the next few hours with light to moderate intensity, with lighter snow expected by the evening as the main precipitation shield shifts to the east, with precipitation beginning to redevelop over the region later tonight as temperatures aloft begin to warm up towards and above freezing. At least 1 to 2 inches of snow are expected in northern NJ, SE NY and interior southern CT, with less than 1 inch for NYC and Long Island. Freezing rain remains a concern in NW NJ and SE NY tonight, with 0.10 to 0.15 inch of freezing rain likely.


11:10 AM: Snow Spreading Into South PA/NJ

nerad253Precipitation began to develop last night in the southern Ohio Valley and continued to spread ENE towards the Mid Atlantic, with moderate snow reported over Maryland along with 1-2 inches of snow. The latest radar, from the Pennsylvania State University e-Wall, shows the heaviest precipitation extending from northeast Kentucky to West Virginia and Maryland; this axis will continue to shift north into the early-mid afternoon, with light to moderate snow expected over the southern half of PA and NJ away from the coast.

The main uncertainty at this time is how far north this band extends, as currently most models stop its northern extent near central NJ, but with a north trend on some of the guidance. This has been most apparent on the 12z NAM which shows moderate snow accumulations into all of northern NJ and NYC, but compared with latest observations its simulated reflectivity shows heavy precipitation extending too far north, suggesting it is likely overdone with snow totals in the area. Currently, I am siding with the moderate snow band stalling just south of the area, although the northern extent will be continued to be watched throughout this afternoon, and should it extend into at least the I-78 corridor, amounts may have to be upped slightly.

Current Forecast: Snow showers are expected to develop between 3-6 PM for most of the area and between 6-9 PM for northern locations; accumulations of less than 1 inch are expected in NYC and the north/west suburbs, with 1-2 inches towards central-western NJ, SE NY and southern CT. As mid level temperatures warm up faster than surface temperatures, a quick changeover to rain is expected for coastal areas with easterly surface winds, while north/west suburbs of NYC and southern CT change to sleet by 12am and rain by 4am, and interior NW NJ and SE NY hold onto freezing rain for a longer period of time with up to 0.10 inch of ice expected, leading to hazardous road conditions on Monday morning before fully changing over to rain.

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