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Live Blog: First winter storm of the season begins in NYC

11:30am Update: There is a bit of a lull right now as the initial band has moved to our east, and lots of precipitation as expected missed us offshore.

But now that the system is interacting with a mid-level disturbance to our west, snow has blossomed again in E PA, and especially in SW Jersey near Philly, and head NE. The core of that heavy band may just miss NYC, but the NYC area will still see some more moderate snow within the hour and perhaps another inch or so of accumulation.

That band will probably head from I-95 and just south and east, hitting most of Middlesex county, probably clip Union county, hit Monmouth county, and then head towards Long Island, where probably another 1-2″ will fall.

There has been some melting during the lull in the action, as surface temperatures have been hovering right around freezing, and rose just above freezing during the lull in some spots. -DS

10:00am Update: Ingredients continue to lineup for heavy bands of snow in the region, particularly around the I-95 corridor or just south of it.

SPC mesoanalysis shows favorable ingredients for snowfall banding located on the I-95 corridor, or just south of it.

SPC mesoanalysis shows favorable ingredients for snowfall banding located on the I-95 corridor, or just south of it.

The image above shows a mesoscale snowfall banding parameter called EPVg. We won’t get overly technical, but it’s basically an index that tells us if we can expect slantwise convection, which is a much stronger type of lifting mechanism for snow bands than just straight convection. The values are more impressive as one heads southeastward, so lots of precipitation will blossom in S NJ and head just offshore, but there is certainly enough of this for heavy bands to traverse I-95, and especially southeast of there, particularly from 10:00am through noon. 1-2″ of snow per-hour can be expected in some of these bands, with around 1/2″ of snow per hour outside of the bands.

The storm is moving quite quickly, so even in the heaviest banding, 6″ will probably not be exceeded. A general 3-5″ snowfall is still expected, with maybe a tad less further NW of I-95 — though even there, slightly higher snow to liquid ratios due to colder temperatures may make up for the lack of precipitation. -DS

9:10am Update: Took this photo about 10 minutes ago in Rockville Centre, NY — shows that even along the coast, the roads became white right away. Be safe out there! -DS

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9:00am Update: Heaviest band of snow has formed in a SW to NE zone from Trenton, through Middlesex, NW Monmouth, Staten Island, NYC, and western Long Island, where 1-2″ of snow per hour can be expected. The ideal snow growth on the models has been realized, as large, fluffy dendrites are falling.

I’m in SW Nassau County, and even here, temperatures quickly fell once the snow started, and it is now accumulating everywhere. Do not let the initial slightly above freezing temperatures fool you if you are along the coast — temperatures fall very quickly once the heavy snow arrives.

Give yourself some extra time on this morning commute. -DS

8:50am Update: Banding and areas of heavy snow have continued to develop and expand some as anticipated. A bit of  warmer boundary layer (near surface) temperatures near the immediate coast will melt the initial snow (may even be a rain/snow mix) upon contact, but as snow rates increase the accumulations should begin. Not many other changes otherwise since the last update. Heavy snow is expected to continue, especially across much of New Jersey into New York City, over the next few hours.

Snowfall total forecasts also remain unchanged (you can view it in our previous article). We are expecting generally 2-5″ throughout the majority of the area (lesser end north, higher end south) with isolated higher totals in areas that sit under banding for prolonged periods of time.

Regional radar imagery as of 8:50am showing blossoming area of moderate to heavy snow throughout the area.

Regional radar imagery as of 8:50am showing blossoming area of moderate to heavy snow throughout the area.

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Week begins with late season winter storm

NAM model forecast precipitation totals through Tuesday. Notice the sharp cutoff in precipitation totals from North to South near New York City.

NAM model forecast precipitation totals through Tuesday. Notice the sharp cutoff in precipitation totals from North to South near New York City.

Historically strong blocking, incredibly low Arctic Oscillation values, and a strong negative NAO have been in place for over 7 days. It was only a matter of time. A strong disturbance moving through the Central United States will move eastward towards the Mid Atlantic Coast, and eventually offshore. The surface low, which initially develops towards the Ohio Valley, will be forced to transfer and redevelop off the coast. However, the northward extent of precipitation will be extremely limited with a sharp cutoff likely. This will throw a serious wrench into the forecast — with a large discrepancy in snow possible over small areas.

Our Storm Total Snowfall Forecast, valid through Tuesday PM.

Our Storm Total Snowfall Forecast, valid through Tuesday PM.

Forecast models have been inconsistent with the developing gradient. As of Sunday evening, the GFS is the “wetter” of the model guidance — and farthest north with the precipitation shield. The NAM (which had previously shown extreme precipitation totals), Euro and SREF remain farther south. The precipitation amounts and intensity become an increasingly important issue due to the time of year. The warm ground and marginally cold low levels of the atmosphere suggest that light precipitation will not accumulate — and may even fall as rain in some locations on Monday.

Accordingly, the forecast remains highly uncertain as we move forward. We have laid out the expected snowfall totals in our Storm Total Snowfall map, but confidence remains extremely low. It is possible that many locations see light snowfall accumulations but only on grassy surfaces. The best chance for solid light to moderate snowfall totals appears to be over Interior Central and Southern New Jersey, where more persistent heavy precipitation is expected.

A Winter Storm Warning from the NWS remains in effect for Southern New Jersey, while a Winter Weather Advisory remains in effect for the remainder of the area.

The periods of snow, which will begin Monday, could linger into Tuesday throughout much of the area. For up to the minute updates on the upcoming storm system, stay tuned to our Facebook and Twitter accounts.