Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
330 PM EST sun Nov 29 2015
high pressure over eastern Canada builds southeast tonight and into
northern New England by morning. The high will then give way to a
storm system over the middle section of the country...which impacts
the region Tuesday into Wednesday. A warm front moves near the
area Tuesday night into Wednesday followed by cold front moving
through on Wednesday. High pressure then builds in for the end of
the week into next weekend.
Near term /until 6 am Monday morning/...
a split flow regime will continue across North America with the
southern branch being the dominant playmaker across the Continental U.S.. the
upper trough across the NE and eastern Canada lifts out quickly as
short wave ridging approaches from the west. Farther west...a cutoff
low continues to spin across the northern plains. The latter of
which will send a storm system north into the upper Midwest...with
its associated warm front approaching from the south Monday night.
In the meantime...polar high pressure over eastern Canada will drop
southeast into northern New England by morning. This will provide a
cold...clear night across the region. Lows will range from around 20
well inland...to the lower 30s NYC metropolitan. This is a few degrees
Short term /6 am Monday morning through Monday night/...
forecast dilemma for Monday is to what extent does stratus develop
beneath the subsidence inversion. Both the 12z NAM...GFS...and 09z
sref show saturation just below 900 mb working in from the coast in
the morning to inland locations by after. Models in past events have
been too aggressive with the low-level moisture. However...model
consensus does support widespread stratus by Monday after. This should
keep Monday high temperatures from getting much higher than the low to middle
40s. Used a blend of the met/mav MOS...which does not have a good
handle on the low clouds. Thus...it could even be a bit cooler.
For Monday night...middle and high level clouds will increase in
association with warm air advection ahead of the storm system over the middle section
of the country. Surface warm front will be working north across the middle
Atlantic region with cold air damming likely along the Lee of the
Light precipitation will overspread the area toward daybreak Tuesday. There is
the possibility for a brief period of light freezing rain across
western portions of Orange County in the lower Hudson Valley. This
is a low probability event and will depend on the extent of the
cloud cover early Monday evening. If there is some clearing...it would
allow for better radiational cooling.
Lows Monday night will range from the lower 30s well inland...to the
lower 40s across Li/NYC. Temperatures will likely become steady by midnight
but could fall slightly with the onset of the light precipitation.
Long term /Tuesday through Sunday/...
unsettled weather pattern to begin the long term period as a complex
frontal system impacts the area Tuesday into Wednesday. First on
Tuesday...models are coming into better agreement with a weak wave
of low pressure developing along the middle Atlantic coast and
tracking to the north-northeast. The 12z European model (ecmwf)/CMC/NAM/sref all take this wave
across the area. However...the 12z GFS and many of its ensemble
members move this wave east of the 40/70 benchmark. Followed a
closer blend of the European model (ecmwf)/CMC/NAM/sref with this package with the
track of this wave. There are strength differences among the models
with this track solution and some of this appears to have to do with
the strength of some shortwave energy as well as how much damming
from the high offshore is allowed to ridge down into the region.
Will show probability of precipitation throughout the day...first starting out as chance
west...to becoming likely late in the day and evening. There
continues to be a chance of some light freezing rain across interior
Orange County at the onset...but confidence is growing that surface
temperatures may be too warm for any ptype but rain at daybreak.
Much of the rain should be light on Tuesday with the lift in the
form of warm advection as the best large scale lift remains well to
the west through the day. As this wave moves to the north and
east...a warm front approaches from the south.
The warm front will be near the area Tuesday night into Wednesday
morning so will continue with likely probability of precipitation...but do think there is a
possibility of a brief lull in steady rain. Late Tuesday night into
Wednesday morning...divergence aloft ahead of shortwave trough and
better forcing should bring widespread rain. Then on Wednesday...a
cold front will swing through the region. Timing differences among
the models continue with the latest 12z cycle. Have elected to
follow timing close to the European model (ecmwf) as the GFS may be too quick to move
the front and shortwave through. Rain tapers off Wednesday night as
the front moves well offshore.
Forecast temperatures average above normal Tuesday and Wednesday.
Thursday-Sunday...dry conditions return to the tri-state. Shortwave
trough lifts to the NE on Thursday with high pressure building from
the southwest. Shortwave energy may linger aloft as as another wave
passes to the north on Friday. There continue to be differences in
the amplitude and timing of this wave. The wave should send another
cold front through Friday night..but the atmosphere looks too dry
for any precipitation. Otherwise...ridging builds aloft and at the
surface this weekend. Temperatures should average near normal during
Aviation /21z Sunday through Friday/...
VFR as strong high pressure builds southeast from Ontario today...
into upstate New York and New England tonight...and then offshore on
North/north-northeast winds less than 10 knots this evening. Winds veer NE and increase
to 10 to 15 knots towards midnight with g15-20kt possible in NYC metropolitan
and along the coast through Monday morning. Winds weaken a bit
Scattered-broken MVFR ceilings likely to develop late Monday morning into
Outlook for 18z Monday through Friday...
Monday aft-night...sct-bkn MVFR ceilings. Light rain possible towards
daybreak...with brief freezing rain possible at kswf.
Tuesday-Wednesday evening...brief freezing rain possible at kswf Tuesday morning.
Rain likely with IFR conds and easterly wind gusts to 20 knots Tuesday.
LIFR possible Tuesday night through Wednesday.
Wednesday night-Thu...becoming VFR Wednesday night. West-northwest winds g20-25kt.
as high pressure builds southeast from from eastern Canada tonight...it
will allow for a tightening of the NE pressure gradient. This will
result in marginal gusts around 25 knots with seas building to around 5
feet. The gradient weakens by middle morning...but it will take seas
until early sun evening to fall below 5 feet.
Small Craft Advisory conds are likely on the ocean Tuesday into Wednesday as a
frontal system impacts the region. Wind gusts up to 25 knots on the
ocean expected Tuesday...with seas 5 to 6 feet. The frontal system
moves away from the waters Wednesday night into Thursday. Small Craft Advisory conds
are likely to continue behind the front. Sub Small Craft Advisory conds are then
forecast on Friday.
a low pressure system could bring approximately one half to one
inch of rain Tuesday through Wednesday.
Marine...Small Craft Advisory from 9 PM this evening to 6 PM EST Monday