Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
100 am EST sun Mar 1 2015
high pressure over the area slides offshore into Sunday. A cold
front approaches from the west late Sunday...then crosses the
area Sunday night. High pressure builds in from the west on
Monday and slides offshore on Tuesday. Low pressure will track well
north of the area Tuesday night and Wednesday...with a warm front
lifting into the area Tuesday night...followed by a cold front
Wednesday and another surface trough late Wednesday night. High
pressure then builds in for the remainder of the week.
Near term /until 6 am this morning/...
850-500 hpa shortwave ridging crosses the area tonight...keeping
things dry. It will also keep the area relatively cloud free until
the ridge axis passes overnight. High clouds approaching from the
west late this evening per infrared.
Forecast is generally on track. Increased lows a few degrees
tonight with middle and high clouds expected to move in during the
latter part of the night. Winds are light and vrb to calm
with clear skies promoting excellent radiational cooling conds.
Temperatures have fallen due to these clear skies and light winds.
Lows are forecast to be around 15-20 degrees below normal -
mainly in the single digits...except 10-15 NYC and western Long
Island. There could be a few areas in far north interior zones that
dip just below zero. Winds will be light...so wind chills will be
at if not slightly below the air temperature.
Short term /6 am this morning through 6 PM Monday/...
models are all in good agreement on the general pattern Sunday-
Monday...but differ in details...particularly at the surface.
Given westerly flow and warm advection pattern on Sunday...expect
precipitation to develop as fast if not faster than the fastest
model...which is the GFS. Have increased probability of precipitation to categorical by
late afternoon as a result. Regardless of model of choice...only
see snow as the p-type during the day on Sunday.
Have sided with higher resolution...especially in the
vertical...ECMWF/NAM/CMC-reg and to a lesser extent the sref with
the idea of a coastal front developing to the S of Long Island
Sunday night...with a weak low of pressure riding along it and
passing to the S of Long Island. This is a feature that has been
observed in multiple other storms with a similar pattern this
winter...and have no reason to believe that this time will be any
The impact of this coastal front with the wave of low pressure
going along it...will be to help keep the low level cold air in
place through most of Sunday night over the County Warning Area. As a result do
not have any area mixing with or changing to rain...however still
expect NYC/Long Island/most of NE New Jersey/S Westchester and Fairfield
to mix with/change to freezing rain late Sunday evening.
With the faster onset...also have a faster end time...with
precipitation coming to an end from west to east after midnight Sunday
Based on this...expect 2-5 inches of snow with up to a tenth of
an inch of ice across NYC/Long Island/NE New Jersey/coastal Westchester
and Fairfield. Expect 3-6 inches of snow elsewhere...except for
possibly 4-7/maybe 8 inches across New Haven/Middlesex/New London
counties. Therefore have issued a Winter Storm Watch from New
Haven County on east in S CT...and a Winter Weather Advisory
elsewhere in the County Warning Area.
Still some uncertainty on quantitative precipitation forecast - with NAM/sref wettest and GFS
generally the driest...with the CMC and European model (ecmwf) in between...and
timing. Also still some uncertainty on timing of any mix/change
over to freezing rain...and if coastal front will indeed stay S of Long
Island as currently forecast.
Temperatures Sunday/Sunday night a blend of mav/met/ecs guidance
and NAM 2-meter temperatures...with an adjustment for wet-bulbing
based on a mav/met blended dew point while precipitating.
Temperatures generally reach middle 20s-lower 30s before the onset
of precipitation...then cool to the lower 20s-around 30 during the
event Sunday evening. Could see a slight rise in temperatures late
Sunday night after the precipitation comes to an end.
Monday should be dry with down sloping boundary layer
flow...despite passage of 500 hpa trough axis. Highs Monday
should be around 5-10 degrees below normal...with all but
possibly higher elevations breaking the freezing mark. Gusty northwest
winds Monday with gusts by afternoon up to 25-35 miles per hour with some
isolated gusts to 40 miles per hour possible.
Long term /Monday night through Saturday/...
models are in decent agreement at 500 mb through the week...although
slight differences in heights begin to take shape during the latter
half from a digging trough in the middle of the country.
Ridging at the surface and aloft tracks towards the East Coast Monday night
with the upper ridge axis sliding east Tuesday afternoon. Precipitation will overspread
the area by Tuesday evening as snow...but with increasing S-SW winds and
strong warm air advection temperatures will warm Tuesday night with snow changing over to rain
from S to north. Warm front lifting towards the area Tuesday night...but
there is some uncertainty if the low level jet will be strong enough to push
it through at the surface. Climatology says no with the low so far to
the northwest...so temperatures in the middle to upper 40s may be too high.
However...do think temperatures should be above freezing but how much
will depend on the amount of melting of the snowpack. This...in
addition to rainfall could lead to minor flooding issues. Cold
front moves across Wednesday followed by another boundary late Wednesday
night. The northern edge of the precipitation shield of a southern stream
system riding along this secondary boundary could keep precipitation
lingering into Thursday...although the trend has been S over the last
12 hours. Have kept chance probability of precipitation for now. Cold weather also returns in
the wake of this second boundary.
Strong Canadian high pressure then builds towards the area into the
weekend with dry weather but the well below normal temperatures
Aviation /06z Sunday through Thursday/...
high pressure will give way to a frontal boundary late in the day.
Expect VFR conditions with increasing middle and high clouds early this
morning. Then visibility rapidly lowers to IFR during middle to late morning
as light snow develops. The snow picks up in intensity after 20z
from west to east...with LIFR possible. By evening...snow
transitions to freezing rain for most airports...except kswf and
possibly CT terminals.
Winds have become light/variable or calm as the high passes
overhead...then light southerly winds are forecast by late morning
or early afternoon.
Outlook for 06z Monday through Wednesday...
Sunday night...MVFR/IFR conditions expected as wintry precipitation ends.
Most likely total runway accumulations...
Monday-Monday night...becoming VFR early. Northwest winds 15-20 knots with gusts
25-30 knots from late morning until around sunset.
Tuesday...chance of snow with MVFR or IFR conditions in the
afternoon at the NYC metropolitan and lower Hudson Valley terminals. VFR
Tuesday night...IFR conditions likely. Snow...changing to a wintry
mix after midnight...and then rain late at all terminals except
kswf. Low level wind shear possible after midnight.
Wednesday...IFR conditions possible in rain...with freezing rain
changing to rain at kswf...and plain rain elsewhere. Low level wind shear
possible in the morning.
Wednesday night...MVFR conditions likely...IFR conditions possible.
Rain...mixing with or changing to snow after midnight.
Thursday...chance of snow and rain with MVFR conditions
possible...ending by nightfall.
a relaxed pressure gradient will keep conditions below small
craft levels through Sunday night with winds 10 knots or less on all
waters through then.
Winds increase rapidly out of the northwest Monday as low pressure
deepens to the northeast. All waters will see at least gusts to
Small Craft Advisory levels with a small chance to chance of gale gusts as well.
Will highlight this potential in the severe weather potential statement.
Sub-advsy conds return late Monday night and continue through Tuesday.
Small Craft Advisory conds then return Tuesday night due to an increasing southerly flow
ahead of a warm front and then behind a cold frontal passage on Wednesday. Gusts
diminish Wednesday night...but seas on the ocean waters will linger into
there is the potential for around 4-6 tenths of an inch of liquid
equivalent to fall Sunday and Sunday night. With all of this
expected to be either frozen or freezing precipitation...no
immediate hydrologic impact is expected.
Between 1/2 to 1 inch of liquid equivalent precipitation is possible late
Tuesday through Wednesday. Most of this will fall as rain...therefore the
combination of this and a melting snowpack could cause minor
Ice will continue to develop on local area rivers and streams as
temperatures remain well below average.
CT...Winter Weather Advisory from 10 am this morning to 7 am EST
Monday for ctz005-009.
Winter Storm Watch from 10 am EST this morning through Monday
morning for ctz006>008-010>012.
New York...Winter Weather Advisory from 10 am this morning to 7 am EST
Monday for nyz067>075-078>081-176>179.
New Jersey...Winter Weather Advisory from 10 am this morning to 7 am EST
Monday for njz002-004-006-103>108.