The overall synoptic evolution among the global models remains in
good agreement with a primary low pressure center to our NW
transferring energy to an offshore low to our south before the
center of the entire system passes through. There are however still
some differences within the mesoscale, particularly with timing,
speed and magnitude of a warm nose aloft. Trend from the past few
runs, even with the GFS, has been warmer in this regard. There are
also differences with the handling of the primary low to our north
and west as well as secondary low pressure near or just south of
Long Island, but somewhat better agreement in this regard versus 24
hours ago.
Precipitation develops across the region from southwest to northeast
late this evening. Strong warm advection ahead of the system is
going to pump warm and moist air up and over the colder and drier
air that will be in place from high pressure to the north. How
quickly a warm nose develops between about 850 mb and 700 mb will
ultimately determine precipitation types and amounts across the
region. The GFS, ECMWF and RGEM are colder than the NAM overall. The
NAM however in the past has done a good job at picking up on warm
noses as well as the speed and intensity of them. The latest
forecast includes a lean toward the NAM given the warming trend
seen, but still averaged with the colder guidance.
Precip begins as all snow, starting late evening/toward midnight
across NE NJ and spreading north and east. A transition to a wintry
mix for coastal areas after midnight, then for the interior after
daybreak Friday. Although the max temp in the warm nose is progged
to eventually be warm enough to preclude anything but rain or
freezing rain, the cold nose beneath it is marginally cold enough
for a refreezing to sleet, but more importantly, deeper than the
typical shallow layer of cold air we more typically see. Therefore
have leaned more toward sleet or a sleet/rain or sleet/freezing rain
in these instances where normally sleet wouldn`t likely be in the
mix. Also, good agreement among the models that late Friday morning
into much of the afternoon will feature a lack of sufficient ice
nucleation for snow growth, so no snow anticipated in the afternoon -
just rain, freezing rain and possibly some sleet. Most of all precip
should fall before early afternoon for most of the area.
There was not enough confidence to upgrade to a Winter Storm Warning
anywhere given the warming trend, and this was collaborated with the
surrounding offices. And with precip starting tonight, felt that
advisories should be posted where needed. Some areas that are not
expected to reach advisory criteria based on snow/sleet
accumulations have been added to the advisory based on combined
snow/sleet totals and ice accretion.
