Winter Storm Live Blog

December 9, 2013 2:00am update:

Most areas from NYC and east have warmed up to above freezing, so precipitation has changed over to a plain light rain.

However, places west of I-95 in Jersey and anywhere north of NYC are still at or below freezing. This will allow more freezing rain and sleet to continue. Despite not much being depicted on radar, light precipitation will fall because the moisture is primarily confined to the surface. The radar beams jump “over” the low-level moisture and are hitting some of the drier air aloft, which is why not much has been detected on radar, despite precipitation falling.

In any visible echoes on radar that do appear, freezing rain and sleet may come down moderately at times for inland areas. Most of the steadier activity has been compressed to the south, but low-level moisture is still prevalent enough to produce light freezing rain and sleet.

NW Jersey and the Hudson Valley may very well remain below freezing all night, which could lead to a treacherous commute tomorrow morning. Fortunately, ice accretion won’t be significant in volume due to the lack of heavy precipitation, but enough will fall to create some problems.

Elsewhere in our region, freezing rain and sleet should change over to plain rain by around 5am, leading to just primarily wet roadways for tomorrow morning.

Recap on the significant snow to our south: In case some of you are wondering what some official snowfall totals were to our south, check out this link:

http://forecast.weather.gov/product.php?site=NWS&issuedby=PHI&product=PNS&format=CI&version=1&glossary=0

It is a compilation of all of the snowfall reports that were sent to the National Weather Service in Mount Holly, NJ.

Particularly impressive amounts include 12″ of snow in Newark, Delaware, 8.0″ of snow in Toms River, NJ, and 8.6″ of snow at Philly International Airport.

Additionally, further to the south, the ice storm is getting pretty bad in the DC Metro area, as some reports have indicated upwards of 8500 power outages (link is time sensitive):

http://www.pepco.com/home/emergency/maps/stormcenter/

Fortunately, we will not have to worry about that in our area.

We are signing off for the night, but check back tomorrow for an update on Tuesday’s potential snow event.

 

December 8, 2013 11:30pm update:

After most of the area saw around one inch of snow, it quickly moved out. Temperatures are slowly warming both at the surface and aloft, as warm air advection is increasing. The high pressure system is moving off the coast, which is helping to shift the winds to a more easterly component (off the Atlantic Ocean), helping to warm things up. Some places on Long Island and near the coast are already slightly above freezing.

Elsewhere, although temperatures are mainly still below freezing at all levels, there is not enough saturation throughout the atmospheric column to support ice crystal formation. Instead, the low-level moisture and saturation will allow for freezing drizzle, so roadways may be a bit slick.

More precipitation is moving in from the south. Freezing rain and sleet will fall in far northern Jersey and the southern Hudson Valley for a few hours, which may make things a bit slick for the morning commute as well.

Further south closer to the I-95 corridor, any sleet and freezing rain will change over to rain before Monday morning’s commute, so roadways will be wet. Still, though, caution should be exercised.

 

December 8, 2013 4:00pm update:

Light snow and flurries have broken out throughout much of the NYC area. More steady snow is in E PA and W NJ, sliding eastward, and will be overspreading much of the region within the hour.

December 8, 2013 3:00pm update:

Heavy snow continues in the Philly to Toms River corridor and especially just south of there! Here is a photo from Southampton, NJ, which is about 30 miles just south of due east from Philadelphia, showing nearly 10″ of snow!

Nearly 10" of snow has fallen in Southampton, NJ. Photo credit goes to Anthony Adams.

Nearly 10″ of snow has fallen in Southampton, NJ. Photo credit goes to Anthony Adams.

What is explaining this heavy snow band? As we talked about earlier, it’s frontogenesis, where a cold high pressure to the north is interacting with the warm, moist air to the south, creating lots of lift.

Storm Prediction Center mesoanalysis shows a 1034mb high pressure system in very close proximity to the heavy precipitation. That leads to strong lifting for precipitation in a narrow area.

Storm Prediction Center mesoanalysis shows a 1034mb high pressure system in very close proximity to the heavy precipitation. That leads to strong lifting for precipitation in a narrow area.

The strong high pressure system is very close to the area of precipitation, which helps the frontogenesis to compress into one solid, narrow band of snow. If the high were slightly north, the frontogenesis would’ve been more spread out, but not nearly as impressive in magnitude, so light to moderate snow would have been spread out over a larger area, as opposed to one narrow, very heavy band of snow.

That being said, the precipitation is gradually edging northward, and snow should begin in the NYC/LI areas by 4:00pm. An inch or perhaps two inches of snow in some localized areas can be expected. The snow will accumulate quickly on roadways, so make sure to exercise caution.

 

December 8, 2013 2:00pm update:

Steady light snow has moved into Monmouth county, and flurries have begun to fall in Middlesex county. Any snow that falls will accumulate quickly, even on the roads, given the cold temperatures and low December sun angle, so make sure to take things slowly if you are traveling.

Dry air is still a hindrance to NYC and LI, as snow probably will not begin until around 4:00pm.

Extremely heavy snow is falling near Philly and eastward, as reports have indicated 2-3″ of snow per hour, as many locations in those latitudes can expect 6″+ snowfall totals. The frontogenesis is maximized in those areas. If anyone wants to see some heavy snow falling, check out the Eagles game!

As alluded to before, the dry air will prevent our area from getting the snow that the Philly to Toms River corridor will get. The cutoff between heavy snow and merely light snow and flurries is still very sharp — a classic indicator of strong frontogenetic forcing.

 

December 8, 2013, 12:30pm update: 

Some of our southern locations have already started to pick up some snow, as a steady band of snow has developed near Philly and eastward. Accordingly, short-range model guidance has increased its snowfall output in parts of Central New Jersey to indicate the potential for several inches. The snow will slowly inch northward as the day progresses. As far as our area is concerned, snow should begin around 3:00pm in southern sections of the Metro region, and closer to 4:00pm in NYC and LI.

The latest run of the HRRR (High Resolution Rapid Refresh Model) shows several inches of snow in Central Jersey, with a bit less further northward thanks to dry air.

The latest run of the HRRR (High Resolution Rapid Refresh Model) shows several inches of snow in Central Jersey, with a bit less further northward thanks to dry air.

The HRRR model, a fairly reliable short-term model, shows several inches of snow from Central Jersey and southward. The model can sometimes be prone to overdone solutions, so we are not going to take this model literally just yet — but we are monitoring the potential carefully

Adding some credence to the models forecast is developing frontogenesis. Frontogenesis features a temperature gradient increasing in a given area — when warm air advection is increasing in a relatively warm location, and cold air advection is increasing in a relatively cold location, and those areas of advection “meet,” then you have an increasing temperature gradient. This causes an area of strong lifting, which helps to produce moderate snow. This process is definitely taking place due to the cold high pressure to the north, and the warm-air advection from the storm system to the south.

It is certainly possible for areas in Central and Southern Jersey to pick up 2-4″ of snow.

Further north towards NYC and Long Island, dry air will be a bit of a bigger problem, due to being further north and closer to the high pressure system. An observed sounding from this morning for Upton, NY shows this dry air being prevalent. This will help to delay the snow’s onset till around 3:00 or 4:00pm, as well hindering some of the intensity.

sundaywinter2

This morning’s sounding from Upton, NY shows a lot of dry air in the lower levels of the atmosphere. This means that NYC and LI will likely not see as much snow as Central Jersey.

Lots of times, when there is an area of lots of lift in close proximity (the Central NJ snowband), the atmosphere balances itself out with an area of subsidence (downward motion) near-by. This, in addition to the dry air, will make it much harder for the snow to initially develop in NYC and Long Island. Additionally, by the time the precipitation makes it further to the north, the frontogenesis might not be able to occur as efficiently, as the surface high pressure system will have moved a bit to the east towards the Atlantic, and not advect as much cold air in the “cold” part of the frontogenesis equation.

That being said, the upward tick in moisture associated with this storm and good warm air advection into a cold airmass should allow our area to pick up an inch of snow — perhaps up to two inches in some localized areas.

Sometime after midnight tonight, the warm air advection aloft will lead to snow changing to sleet for a couple of hours, and then to freezing rain for the interior, and cold rain for the coastal areas.

We will update this live blog throughout the day as the storm makes its approach regarding the timing of the snow and any changeovers.

 

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