Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
732 am EDT Tuesday Sep 30 2014
a back door cold front will slowly move through this morning.
Multiple upper level disturbances will then affect the area
through middle week...followed by high pressure building from the
north Thursday into Friday. A cold front will pass through on
Saturday...followed by high pressure building in on Sunday.
Near term /until 6 PM this evening/...
shortwave with associated vorticity maximum moving through the region this
morning...continuing to trigger light rain with patchy drizzle over
Long Island...NYC and southern CT. Very moist lower levels resulting
in areas of fog....with patchy dense fog...over areas outside of NYC
metropolitan. Have added to forecast through middle morning and issued an
Special Weather Statement to address the sudden visible changes.
Low level flow turns to east-NE in the wake of a passing back door
cold front this morning. As the front continues to push slowly
west-southwest-Ward and a weak upper trough moves across...should see more
showers today especially as the combo of daytime surface heating and
middle level cooling via the upper trough increases instability. NAM
soundings show scape of up to 500 j/kg...enough to help generate
showers but not thunder with the instability confined mostly below
the freezing level. Forecast likely pop mainly for Long Island...with
Short term /6 PM this evening through 6 PM Wednesday/...
scattered to numerous showers should continue to be around tonight into
Wednesday as an upper low approaches from the west...then moves across
on Wednesday. The upper low will interact with a developing inverted
trough extending northwest-Ward from offshore low pressure on Wednesday...
with potential for locally heavier rain of over an inch near and
just east of where this interaction occurs...which is still
uncertain due to its mesoscale nature. The 00z NAM/GFS and 29/12z
European model (ecmwf) were pointing toward southeast CT and eastern Long Island...while the
00z European model (ecmwf)/03z sref are farther east.
Cloudy skies and and east-NE flow of maritime air will persist...with
temperatures a couple of degree above average today...then near or slightly
below average on Wednesday.
Long term /Wednesday night through Monday/...
lingering chance for precipitation Wednesday evening...mainly over eastern areas...as
strong upper level shortwave closes off and pushes east. 00z model
suite in general agreement with rain showers ending over areas west
of NYC by 06z...and then eastern areas by Thursday morning. While a
brief heavy downpour is not out of the question Wednesday evening...the
trend with the models has to push it east...most likely occurring
outside the County Warning Area. Dry conditions then setting up through Thursday night-Friday
with surface high dipping south between two surface low pressure
systems...and ridging aloft.
Attention then turns to an approaching low pressure system for the
first half of the weekend. Slight discrepancies with 00z models with
GFS the fastest solution and European model (ecmwf) the slowest. However...it should
be noted all models are now trending faster for the progression.
Depending on the strength of the ridging...the models could be
weakening it too quickly and thus bringing the front and associated
precipitation through quickly as well. As such...slightly adjusted the timing
of the precipitation Friday night-Sat...but did not want to deviate too much from
prior forecast until a good handle of the trend can be made.
Confidence exists it will rain on Saturday...figuring out the timing
will need to be ironed out in subsequent forecasts. Dry weather on
Friday...then began probability of precipitation after 00z Sat with the passing of a weak
shortwave out ahead of the main upper level low. Have likely probability of precipitation in by
12z Sat morning and then taper probability of precipitation off west to east Sat night as
main forcing aloft swings through the northeast.
Surface high builds in the wake of the front Sunday-Monday while the
region remains under broad troughing. Have dry weather in for sun-Monday
with the next chance of precipitation coming by Monday night.
Near seasonal temperatures in place through Sat. A brief burst of cold air advection behind
the front will send temperatures down a degrees below normal for Sat
night-Sun night. However...return flow quickly sets up with the high
pressure building in...pushing temperatures back to near normal by Monday.
Aviation /11z Tuesday through Saturday/...
a cold front is sliding south across the New York metropolitan this morning.
The front sags south of the region this morning as high pressure
builds over New England.
IFR ceilings are located behind the front. These are now into klga and
kisp as of 11z. Expecting slow improvement by middle morning from east
to west...though unsure of timing details and rate of improvement.
Fairly confident that we'll be VFR in the afternoon with western
sections the last to improve.
Some light rain with scattered showers possible eastern sections
New York metropolitan enhanced aviation weather support...
Detailed information...including hourly taf wind component forecasts
can be found at: http:/www.Erh.NOAA.Gov/zny/n90 (lower case)
JFK fcster comments: uncertainty in ceiling height this am with IFR
possible around 13z. High confidence in east surface wind less than 10
Klga fcster comments: expect gradual raising of the ceiling this
morning. High confidence in surface wind forecast.
Kewr fcster comments: uncertainty in arrival time of MVFR ceiling this
The afternoon kewr haze potential forecast is green...which
implies slant range visibility 7sm or greater outside of cloud.
Kteb fcster comments: uncertainty in ceiling height this am.
Khpn fcster comments: confident in the improvement this
morning...though uncertainty in the timing.
Kisp fcster comments: timing of ceiling improvement could be +/- 1-2
Outlook for 12z Wednesday through Saturday...
late t0night...MVFR or lower ceilings possible. Chance -shra east-NE winds
around 10 knots.
Wednesday...MVFR locally IFR cigs/vsbys/-shra. East-NE winds 10-15 with g
20 knots along the coast.
Thursday...chance MVFR mainly am. NE winds around 10 knots.
Friday...VFR. Southeast-S winds around 10 knots.
Sat...rain likely - MVFR or lower in the am. SW winds am becmg west-northwest
PM. Gusts 20-25kt likely late.
increasing east-NE flow in the wake of a back door cold frontal passage...as
the waters become sandwiched between high pressure to the north
and developing offshore low pressure...should lead to Small Craft Advisory conds
tonight into Wednesday night...and possibly Thursday. Small Craft Advisory remains for late
this evening through Wednesday afternoon as flow increases to 20-25 knots
and seas build to 3-5 feet by late evening...and to 4-7 feet on Wednesday.
Generally expecting sub-Small Craft Advisory conditions on all non-ocean waters
through the coming weekend. For the ocean waters...occasional gusts up
to 25 knots will be possible Wednesday night into Thursday...with the winds
diminishing as high pressure builds in Thursday. Could see another chance
for 25 knots gusts right ahead of the front Friday night-Sat...then
Sunday with cold air advection over the waters. Seas building in response to
increased winds middle week...expecting 4-6 feet seas through Thursday before
subsiding with the diminishing winds. Seas will build to 5-7 feet
for the weekend before dropping to less than 5 feet once again
no significant precipitation expected through Tuesday night. A few tenths of
an inch of rainfall...and locally up to an inch...are possible
Wednesday-Wednesday night...mainly southeast CT and eastern Long Island. Between one half
to one inch of rain is also possible with cold frontal passage
Marine...Small Craft Advisory from 11 PM this evening to 6 PM EDT
Wednesday for anz350-353-355.