Winter Weather Advisory now in effect for Nassau and Suffolk
Counties 9pm this evening through 7am Wednesday morning.
Low pressure beginning to develop over the southeast this
afternoon and will push ENE off the southern Middle Atlantic
this evening into tonight. The region will continue to lie on
the northern periphery of the precip shield. The latest model
trends all support a bump up in liquid equivalent with around a
few hundredths well inland, around a tenth southern portions of
the Lower Hudson Valley and coastal CT, 0.15-0.20" in the NYC
metro, and around 0.25" across Long Island. The NAM still
appears to be the wettest of the guidance across the area,
especially across the southern half with as much as 0.3" in NYC
and 0.4" across eastern Long Island. Much of the 12z CAMs have
come into better agreement and have been noting slow trends in
the HRRR to slowly increase precip amounts across the area. The
HRRR in past lighter events on the northern periphery has run a
bit too low, so this has been factored into the latest forecast.
There are several key ingredients that support the trend upward
including a stronger 700mb frontogenesis signal combining with
strong upper divergence from a 170-190 kt departing polar jet
streak to our north. Models do tend to struggle with the
combination of these features and have seen several past events
over perform with lift accompanying a strong upper jet. The
other factor is the majority of the model suite is indicating
enhancement of the precip shield from Southern NJ up into the
area tonight as the coastal low emerges off the coast. Thermal
profiles are also supporting an all snow event. Soundings also
indicate deep ice saturation within the dendritic growth zone
for several hours tonight, especially across Long Island and
portions of the NYC metro. The strongest lift appears to occur
between 10pm and 2am with a decrease the rest of the night.
The snow will begin to overspread from the south tonight between
7-9pm, becoming steady and continuing through the early morning
hours. There is a period between about 10pm and 2am where
snowfall rates could run between 0.25-0.50" per hour. There is
even a low probability snowfall rates could briefly approach 1"
per hour across Long Island from around 11pm-1am as the
strongest forcing and deepest moisture combine. Snowfall rates
will drop off from west to east from 3am to 5am. Some flurries
may linger towards day break, but accumulating snow should end
before sunrise.
Snow to liquid ratios look higher with this event given we are
on the northern periphery of the low and soundings show more of
an ice saturation signal over one with deeper supercooled water
saturation signal. For these reasons have gone closer to a
12-13:1 ratio.
Updated snow totals in the are around 3 inches with potential of
a few spots approaching 4 inches. Elsewhere across the NYC metro
and much of NE NJ and coastal CT, generally 1-2 inches are
forecast. Locations closer to the south shore in Staten Island
and southern Brooklyn and southern Queens could see up to 3
inches. Amounts across the interior will be lower and generally
less than an inch.
Have also issued a Special Weather Statement for areas outside
the advisory where 1-2 inches is expected to account for
potential of slick conditions tonight.
