Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1043 am EDT Tuesday Sep 2 2014
a cold front approaches from the west this afternoon...then
crosses the tri-state tonight. Weak high pressure builds in on
Wednesday...then remains over the region into Friday. A cold front
will approach Friday night and move across the region Saturday and
Saturday night. High pressure returns for the start of next week.
Near term /until 6 PM this evening/...
fog has dissipated across much of the area with the exception of
a few patches along the coast near southeast CT and the South Fork near
Montauk. Very high dew point air...70 to 75...traversing the
cooler near shore waters has allowed for this fog. This though
should not last much longer due to daytime heating and slightly
lower dew points by after.
Otherwise...convective forecast for today is a challenging one.
While a pre-frontal trough will develop and remain over mainly
western/northern zones...appears should have a weak cap develop
around 650 hpa. So even with 1500-2500 j/kg of cape forecast...the
weak cap coupled with best dynamic forcing prognosticated to our north...and
relatively weak shear 20 knots or less until maybe very late in the
day over far west zones as low-middle level jet approaches there.
Appears best chance for any convection is over areas north/west of NYC
late this afternoon with arrival of low-middle level jet.
Given above...feel that most likely cap holds on over the southeast 2/3
of the County Warning Area...so have gone with a dry forecast there. Have chance
probability of precipitation by late afternoon over mainly Orange and Putnam counties and
slight chance probability of precipitation in between. Any convection that does form will
be mainly of the pulse variety...with some multi-cellular
structures possible by late afternoon over mainly Orange County
with arrival of low-middle level jets. Based on this feel severe
threat is minimal this afternoon...but cannot be completely ruled
High remain on track for the upper 80s to lower 90s with heat
indices approaching 100 in metropolitan New York.
There is a moderate risk of rip current formation at Atlantic
Short term /6 PM this evening through 6 PM Wednesday/...
region will be in the right rear quadrant of 80-90 knots 300 hpa
jet...passing of strengthening low-middle level jets in the
evening...and the area under diffluent flow in the middle
levels...coupled with precipitable waters forecast to increase to
around 2 inches...then have the potential for locally heavy
rainfall in any storms that do form this evening. Refer to hydrology
section of the afd for further details.
However...will be working against diminish cape with the loss of
solar heating...with best dynamics passing to the north...believe that
any severe potential rapidly diminishes during the early evening
hours...and it was not all that high to begin with.
700-500 hpa shortwaves lifts to the North/East of the area tonight...with
zonal flow developing Wednesday...allowing for things to dry out
late tonight behind the shortwaves.
For lows tonight...used a blend of mav/met guidance with NAM
2-meter temperatures...with values forecast to be around 5 degrees
above normal. For highs Wednesday used a blend of mixing down from
850-825 hpa per BUFKIT soundings...with NAM 2-meter temperatures
and a blend of mav/met guidance. This yields highs around 5-10
degrees above normal.
Long term /Wednesday night through Monday/...
high pressure over the region Wednesday night through Friday will
keep conditions sunny and dry. As the high moves offshore on
Thursday...expect humidity levels to increase Thursday night and
A cold front will approach the area Friday night into
Saturday...pushing offshore sometime Saturday night. Expect showers
and thunderstorms to accompany the front. Most of the models are in
good agreement on the timing of the front. However...a few of the
models want to linger some precipitation into Sunday behind the
front. For now...do not want to rule this out...so will keep some
chance/slight chance probability of precipitation in for now.
High pressure over Canada will build south behind the cold
front...bringing cooler and less humid conditions to the region for
the start of next week.
Temperatures Thursday through Saturday will remain above normal with
highs in the middle to upper 80s. Slightly cooler conditions can be
expected right along the coastal sections. Temperatures then fall
below normal Sunday through Tuesday with highs only in the 70s.
Aviation /15z Tuesday through Saturday/...
a cold front approaches today and passes through tonight.
VFR. Isolated/scattered thunderstorms with brief sub-VFR conds this afternoon and
evening...possibly as early as around 19z...but more likely to occur
after 00-01z. Not enough confidence in coverage and placement to
include in tafs.
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)
Kjfk fcster comments: sea breeze shift could be around an hour off
in either direction.
Klga fcster comments: sea breeze could potentially shift winds to
the south around 21z. Not enough confidence to include this shift
Kewr fcster comments: occasional gusts 15-18 knots.
The afternoon kewr haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.
Kteb fcster comments: any amendments most likely related to thunderstorm
Khpn fcster comments: any amendments most likely related to thunderstorm
Kisp fcster comments: any amendments most likely related to thunderstorm
Outlook for 12z Wednesday through Friday...
Sat...sub-VFR possible in scattered shra/tsra.
winds will be 15 knots or less on the waters through Wednesday.
There is some potential that seas could build to 5 feet on anz-350
tonight...with tightening of pressure gradient ahead of the
front...and residual 1-2 feet swells. However confidence in this is
not all that high...so do not reflect in forecast at this time.
Seas should come down on Wednesday with a weakening pressure
gradient over the area.
Generally looking at sub-Small Craft Advisory conditions on the area waters Wednesday
night through the weekend. A cold front will push across the waters
Saturday night into Sunday...which will result in higher winds and
spotty rain showers/thunderstorms mainly over areas north/west of NYC...could produce
isolated locally heavy rainfall. Areas experiencing locally heavy
rainfall could experience minor urban/poor drainage flooding.
Outside of areas experiencing locally heavy rainfall...less than
0.2 inches of basin average precipitation is expected from any
precipitation that does fall this afternoon and tonight.
It should then be dry from Wednesday through at least Friday.
long term...British Columbia