Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1233 am EST sun Dec 21 2014
a weak upper level disturbance will cross the area late tonight
into Sunday morning...otherwise high pressure remains nearly
stationary to the north across the Saint Lawrence River valley
for the remainder of the weekend. A warm front approaches Monday
afternoon...and remains south of the area Tuesday and Tuesday
night. A storm system will impact the area Tuesday night through
Wednesday night...ending early Christmas morning. High pressure
builds in late Thursday into Friday. Another low will affect the
region next weekend.
Near term /until 6 am this morning/...
flurries continue to be reported over mainly eastern sections of
the County Warning Area. 00z sounding only shows saturation to about
-10c. However...proximity to the ocean and therefore sea salt may
act as ice nuclei...which can form ice crystals at warmer temperatures.
The only area that might see some rain mix in is the Twin Forks
of Long Island and perhaps portions of New London in CT. Mesoscale
models show that the precipitation should continue overnight...though the
temperature/dewpoint spread should only amount to flurries.
However...cannot rule out a dusting or coating in some
spots...especially higher elevations of CT. Otherwise...forecast
is on track with only minor changes made to reflect current observation.
Cloud cover and a northerly flow today kept temperatures in check with
afternoon highs only in the upper 20s to the lower 30s. The last
day of autumn will finish as one of the coldest. Winter solstice
is 603 PM Sunday evening.
Cold high pressure settles over the Saint Lawrence River valley
this evening. This will maintain the cold air supply with light
northerly winds. Low-level moisture will also remain trapped beneath a
strong inversion at approximately 900 mb. Thus...looking at
continued cloudy skies tonight. This will keep temperatures from dropping
too fast with lows ranging from the lower 20s well inland to around
30 at the coast.
A short wave trough over the Ohio Valley this evening will move
across the area late tonight. This coupled with the low-level
moisture may provide just enough lift for snow flurries or very
light snow...with the best chance being across eastern Li and southeast
CT. Little or no snow accumulation is forecast. There could also
be some rain mixed in and/or freezing rain with lack a ice
crystals in the cloud bearing layer. Often though along the
coast...sea salt can lower the activation temperature of ice nuclei.
Short term /6 am this morning through 6 PM Monday/...
morning flurries and/or sprinkles will give way to partial
clearing by after as short wave ridging builds in aloft. Far
eastern Li and southeast CT could stay mostly cloudy all day due to
deeper moisture in place beneath an inversion.
Highs on sun will approach 40 along the coast,,,but a few degrees
cooler inland. This could vary based on the extent of clearing.
High pressure builds slowly south and east into the Canadian
Maritimes...with low-level northerly winds gradually veering Sun night.
Lows will once again be in the 20s Sun night...but the extent of
the cloud cover remains somewhat uncertain as the flow becomes
Long term /Monday night through Saturday/...
a weak wave of low pressure develops along the southeast coast
Monday...and will be on a developing warm frontal boundary. This low
remains weak as the warm front moves slowly north Monday night into
Tuesday. Meanwhile high pressure over New England into southeastern
Canada weakens. At the upper levels a full latitude trough develops
Monday front central Canada into Mexico with surface low pressure
deepening in the upper Midwest. During Wednesday the trough becomes
negative with the low moving through the western Great Lakes. The
warm front is expected to remain south of the region Tuesday into
Wednesday. So with weak lift developing ahead of the warm front will
keep chance probability of precipitation Monday afternoon into Tuesday. Guidance is no
longer deepening with coastal low and keep the low over the Great
Lakes as the primary low with the negative trough. As the lows cold
front approaches late Tuesday night into Wednesday...a strong low
level jet to near 70 knots develops. With a deep southerly flow
limiting mixing strong gusty wind will be limited. However the low
level jet will provide strong lift during Wednesday and periods of
moderate to heavy rainfall is expected. Warming occurs Tuesday into
Wednesday with all liquid during this timeframe. Before
that...Monday night...some light snow and rain will be possible
inland...however no accumulations are expected. The thermal profile
of the GFS was slightly warmer than the 20/00z European model (ecmwf) and used a
blend for p-type.
As the parent low moves into southeastern Canada late Wednesday into
Wednesday night a cold front will cross the region after 05z into
early Thursday morning...passing just east of the area around 12z
Thursday. With timing consistency have kept the likely and
categorical probability of precipitation for Tuesday night through Wednesday night.
In the colder air behind the front Thursday and with cyclonic west
to northwest flow...strong and gusty wind will be likely. Have kept
below advisory criteria for now...however gusts could be close to 45
knots at times Thursday.
High pressure builds in for Friday with lighter winds. Then for
next weekend another inland low pressure system will impact the
Aviation /06z Sunday through Thursday/...
high pressure builds over the area for the remainder of the
weekend and departs early in the week.
All terminals with the exception of kjfk is MVFR...but they too
should be dropping shortly with the approach and passing of an
upper level disturbance. Light snow and/or flurries possible
mainly east of NYC...but not expected to impact visibility and chc's aren/T
high enough to include in tafs.
May be too optimistic with ceilings in NYC metropolitan at 12z and MVFR could
linger into the afternoon. Then conds expected to drop back to MVFR Sun
night. Guidance is agreement east of NYC that MVFR ceilings remain
through the taf period.
Light and vrb winds overnight...then light northerly winds could back
20-30 degrees more to the left of forecast during the day
sun...before becoming light and vrb again Sun night.
Outlook for 06z Monday through Thursday...
Monday-Monday night...MVFR or lower possible in east flow. Chance of rain.
Tuesday-Tuesday night...IFR likely in rain...ceilings and visibilities. East winds
10-20 knots...becoming southeast.
Wednesday...high impact event possible...IFR likely with heavy rain and
gusty southeast winds 25kt+ shifting to SW late Wednesday.
Thursday...sub VFR early in showers...then VFR with gusty westerly
winds 20-25 knots g40 knots.
forecast on track...no changes at this time.
With high pressure building north of the waters...can expect north
winds 10 knots or less through the weekend along with seas generally
1-2 feet on the ocean or 1 feet or less on all other waters.
A light east to southeast flow Monday into Tuesday ahead of a warm
front will remain below small craft levels...with seas also
remaining below 5 feet. Deepening low pressure moving through the
western Great Lakes Wednesday with a cold front approaching the area
waters will result in an increasing southerly flow. Small craft wind
and seas will be possible on the ocean late Tuesday into Tuesday
night...and across all the waters Wednesday. Then in the colder air
behind the cold front Thursday wind gusts will be gale force across
all the waters and remain into Thursday night with gusts diminishing
toward Friday morning...with gusts below small craft later Wednesday
morning. Seas on the ocean waters will remain at small craft levels
rainfall from Monday afternoon through Wednesday night could total 1
to 2 inches with locally higher amounts. Much of the rainfall is
expected to occur Wednesday into Wednesday night. Minor urban and
poor drainage flooding is possible.