Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
935 am EST sun Nov 23 2014
a warm front slowly approaches from the southwest through this
evening...then lifts to the north late tonight and Monday morning.
A cold front follows behind it Monday night...then a secondary
cold front passes on Tuesday. Weak high pressure then builds in
Tuesday night. An area of low pressure off the southeastern
Seaboard Wednesday morning...tracks northeast to the Canadian
maritime provinces by Thursday evening. High pressure then builds
in from the west into Friday...followed by a Alberta clipper
system impacting the area Saturday.
Near term /until 6 PM this evening/...
added schc for sprinkles this morning based on radar. Otherwise...no
other changes made.
Otherwise...a deep layered ridge builds over the area today. Will
see decreasing cloud cover in response to associated subsidence
with areas partly to mostly sunny by late afternoon.
For highs today...used a blend of mav/met/ecs guidance with NAM
2-meter temperatures and a mix down from 975 hpa per BUFKIT
soundings. Highs should be near to slightly above normal.
Short term /6 PM this evening through Tuesday/...
the deep layered ridge lifts to the northeast this
evening...allowing for low-middle level moisture to quickly build in
behind it. With diffluent flow developing aloft and passage of a
60-70 knots low level jet...expect moderate...to possibly locally
heavy...rainfall overspreading the entire area after midnight
ahead of the surface-850 hpa warm front.
There is sufficient elevated instability over eastern zones...with
showalter indices forecast to between 0 and 2...along with the
aforementioned low level jet...that have continued with a
slight chance of thunder there.
Precipitation should taper off to -shra by late Monday morning as
the warm fronts lift to the NE. Refer to the hydrology section of
the afd for details on amounts and any potential impacts.
Also with the passage of the aforementioned low level jet...there
could be isolated wind gusts of 40-50 miles per hour in any embedded
convection...with the best chance over eastern zones late
tonight/Monday morning - and damaging wind gusts cannot be 100
percent ruled out. It should end up quite windy once in the warm
sector Monday afternoon and evening...with gusts up to 30-40 miles per hour.
Isolated stronger gusts are possible...however confidence in there
occurrence and areal coverage is not high enough to warrant a Wind
Advisory at this time.
For lows tonight a blend of mav/met/ecs guidance and NAM 2-meter
temperatures was used...with values forecast to be around 10-15
degrees above normal. Expect the lows to occur in the
evening...then temperatures to rise into the 50s
overnight...except middle-upper 40s far northwest Orange County.
Record highs quite possibly will be set on Monday at many
locations...with the region solidly in the warm sector in the
afternoon. The main question is how much clearing will occur once
there. For now appears should be sufficient to support highs
around 15-20 degrees above normal. This is consistent with a blend
of mav/met/ecs guidance with a mix down from 975-950 hpa per
BUFKIT soundings and NAM 2-meter temperatures. Refer to the
climate section of the afd for details.
Should have sufficient low level moisture to see an isolated-scattered rain showers
ahead of the cold front Monday evening. Then clearing in its wake.
For lows Monday night a blend of mav/met/ecs guidance and NAM
2-meter temperatures was used...with values forecast to be around
15 degrees above normal.
Tuesday will feature SW flow aloft...and as currently forecast to
be absent any shortwaves embedded in the flow...it should be dry.
For highs used a blend of mixing down from 900-850 hpa per BUFKIT
soundings with mav/met guidance and NAM 2-meter temperatures.
Highs should be a few degrees above normal.
Long term /Tuesday night through Saturday/...
there are still differences between the models...but now the
respective ensemble means generally supporting the GFS (though the
European model (ecmwf) ensemble mean is farther w). With the GFS and CMC trending
stronger (around 10 mb deeper than last night) and farther
west...have opted to use a European model (ecmwf)/GFS blend as there is increasing
evidence that a solution in between the two seems the most
Until all the key players...including energy still out over the
Pacific are resolved...the exact nature of interaction between a
northern stream clipper and a positively tilted trough over the east
central portion of the country by midweek is still uncertain - so
the forecast will likely change to some degree. For now though the
following is what appears most likely - that a fairly decent...but
not overly strong low should track just east of the 40n/70w
benchmark Wednesday evening.
The blend would suggest that light rain could reach Long Island
and maybe far southeast CT late Tuesday night possibly mixed with snow.
The precipitation should then spread northwest fairly quickly Wednesday
morning...possibly starting as a brief period of snow inland
before turning to all rain. As the low nears the benchmark
Wednesday evening...enough low level cold air should come in
behind it to change all precipitation to snow during Wednesday
night...from northwest to southeast...throughout the County Warning Area. The exact timing of
this is uncertain. Precipitation should taper off from SW to NE
Thursday morning...unless the deformation axis lingers over the
area...which is suggested by the European model (ecmwf). For this reason just went
with slight chance probability of precipitation through the day.
The European model (ecmwf) taken by itself would suggest the possibility of warning
level snows to the west/north of NYC...while the GFS solution suggests
the possibility of warning level snows farther east. Given
this...there is a 30 percent confidence of reaching warning level
snow accumulations across the County Warning Area...so will reflect this in the
severe weather potential statement. Fortunately it looks like most...if not all...accumulating
snow will occur mainly Wednesday night so the impact on the bulk
of pre-Thanksgiving travel should be minimized.
Zonal then SW flow builds in behind the system into Friday...then a
weak Alberta clipper passes to the north on Saturday...possibly
leading to coastal development near Cape Cod. Based on this have
slight chance probability of precipitation in over eastern zones Friday night and
Saturday...with the clipper itself likely passing to far north to
bring any precipitation by itself until the coastal low forms.
For temperatures Tuesday night-Saturday a blend of
mex/men/ekd/ece/ecm/wpc guidance was used...with NAM 2-meter
temperatures blended in Tuesday night and GFS and European model (ecmwf) 2-meter
temperatures blended in Wednesday and Wednesday night.
Temperatures will remain below normal through the long term.
Aviation /15z Sunday through Thursday/...
high pressure remains offshore today. A warm front approaches and passes
VFR through around 03-05z Monday. Rain with IFR develops shortly
SW winds will generally average around 10 knots or less into the
afternoon. Winds at kbdr/kgon may back more to the south late
this afternoon. Otherwise...all terminals back to the south at some
point by midnight and increase overnight.
Low level wind shear is likely late tonight into early Monday
morning with winds at 2000ft ranging from 50-65 knots.
Outlook for 12z Monday through Thursday...
Monday...improving conds. Morning rain showers. South winds around 20 knots
with 25-35 knots gusts.
Monday night...mainly VFR. Winds shift to the west at 10-15 knots.
Tuesday...VFR. West-southwest winds 15-20 knots with 20-30 knots gusts.
Tuesday night...diminishing winds. Sub-VFR ceilings possible late.
Wednesday-Wednesday night...low to moderate confidence forecast
with passage of coastal low. Accumulating snow threat possible for
the interior...but accumulating snow could occur closer to the coast
during Wednesday night based on track of low. Strong winds possible
depending on track of low as well.
Thursday...low confidence forecast. Lingering rain/snow showers
possible. Strong winds possible as well.
let the western ocean Small Craft Advisory expire. Still appear on track for Small Craft Advisory conditions
though midday for anz350-353.
Seas might take an hour or two past the Small Craft Advisory end time to fall
below 5 feet on the ocean waters...so Small Craft Advisory end times might be further
adjusted later this morning.
A relatively tranquil period then follows this afternoon into
this evening as a high pressure ridge pivots through.
Winds pick up late tonight into Monday morning with a tightening
pressure gradient and the approach and passage of a 950mb low
level jet of 60-70kt. Have therefore gone with a Gale Warning for
the ocean waters...eastern Long Island Sound...and the Long Island
bays late at night through Monday afternoon. Small Craft Advisory for the other
waters during the same period.
Although winds diminish Monday night...Small Craft Advisory conditions still
probable for all waters through at least Tuesday morning. Seas on
the ocean will take longer than this to subside below 5 feet. Looks
like by midnight Tuesday night...all waters will be below advisory
The next storm affects the waters late Wednesday afternoon through
Thursday with a coastal storm passing nearby the 40n/70w benchmark
Wednesday night. For now...Small Craft Advisory conditions forecast...but there is
potential for gales. Confidence not high at this time.
around 3/4 to 1 inch of rain is forecast from late tonight through
Monday. Any locally heavy rainfall may result in urban/poor drainage
flooding locally. The heaviest rain will occur during the morning
rush hour Monday morning...with the most likely impact being to
slow the commute due to wet roads.
There is increasing potential for 1/2 inch or more of quantitative precipitation forecast to fall
from late Tuesday night into Thursday morning. At this time there
is too much uncertainty to specify any impact...other than to note
that some portion of this should fall in the form of snow. At this
time it appears that the best chance of getting more than 1/2 inch
of quantitative precipitation forecast would be over Long Island and S CT.
record high temperatures for Monday 24 November...
* also occurred in previous years
Marine...Small Craft Advisory from 1 am to 6 PM EST Monday for anz335-
Gale Warning from 1 am to 6 PM EST Monday for anz330-340-345-
Small Craft Advisory until noon EST today for anz350-353.