.NEAR TERM /THROUGH FRIDAY/...
Some weak shortwave energy is traversing across the region
this afternoon within a nearly zonal flow aloft. A few snow
flurries and ice pellets have been reported under some light
returns, but expect the activity has diminished as the energy
departs. The low level atmosphere is very dry still as high
pressure ridges down from southeast Canada.
Attention then turns to a strong vortmax approaching from the
Great Lakes region overnight. In response to this system, low
pressure develops over the Ohio Valley tonight with a weaker
secondary wave possible forming near or just south of Long
Island late tonight into Friday morning. The primary low will
become absorbed into the secondary low by Friday afternoon as
the system departs off the New England coast.
The global models and high resolution models have continued to
come into better agreement on both the large scale evolution
and the mesoscale. This has led to increased forecast confidence
over the last 12 to 24 hours. No changes were made to the
coverage of the winter weather advisories, but have adjusted the
end time to 10 am Friday for NYC metro and NW Long Island and 3
pm Friday for southern Connecticut.
Precipitation develops from southwest to northeast across the
region late this evening into the early morning hours. Strong
warm advection in the middle levels may be briefly offset by wet
bulb cooling and precipitation dynamics. This will yield a
quick burst of snow even at the coast. However, the snow will be
short-lived and may quickly mix with or change completely to
sleet shortly after precip onset due to warm air aloft. An
increasing easterly flow will then help boost surface
temperatures above freezing around day break. This will
effectively bring a change to plain rain across Long Island and
southern portions of the NYC metro. There could be a brief
period of freezing rain, specificually for the NYC metro and NW
Long Island around day break which could bring a light glaze of
ice. For this reason, have left the Winter Weather Advisory in
place here especially due to the timing around the morning
commute.
Away from the immediate coast, there will likely be a few more
hours of snow, possibly moderate to locally heavy at times.
Interior NE NJ, the Lower Hudson Valley, and interior SW CT will
lie just on the colder side of the thermal gradient initally,
which briefly enhances frontogenesis. Snowfall rates of around 1
inch per hour are possible here early Friday morning through
around day break.
The middle level low track of this system is not favorable for
precipitation to remain all snow across the interior. The track
of the low well to the north and west of the area will allow
the warm advection aloft to bring temperatures between 850 mb
and 700 mb above freezing. This will change the snow to sleet
initially as the low level cold air looks dense enough. However,
easterly flow will warm the low levels bringing a change to
freezing rain and potentially rain before ending around midday.
Locations along the CT coast and southern Lower Hudson Valley
will see a bit more snow/sleet than closer to NYC metro and
Long Island, but the warming both aloft and at the surface will
bring a transition to freezing rain and then plain rain shortly
after day break.
By mid morning, saturation aloft diminishes and the precip intensity
likely drops off. Most locations should see liquid precip with the
highest chance of freezing rain across the interior.
Total snow/sleet accumulations have been adjusted downward given
the continued warming trend. These amounts may need to be
adjusted downard further, especially if the transition to sleet
is quicker. 2 to 5 inches of snow/sleet is expected across the
interior, highest along and north of I-84, dropping to less than
an inch for much of NYC and Long Island.
Total ice acretion amounts remain similar overall with a glaze
to a tenth across the NYC metro, SW CT, NW LI, to one to two
tenths further inland.
The models have trended faster with the end of the precip and
have adjusted the forecast accordingly with mostly dry
conditions in the afternoon except for southeast CT. No precip
is expected during the evening commute. Highs should reach the
middle and upper 30s, to around 40 at the coast. Winds are not a
concern with the system, but could gust to around 20-25 mph
near the coast in the morning. Winds will pick up behind the
system late Friday, gusting 25-30 mph by evening. No precip is
expected for the Friday evening commute.
