Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
723 PM EDT sun Jul 5 2015
high pressure will build over the Atlantic through the beginning
of the week. A cold front will then move through Wednesday into
Wednesday night...then stall just to the south on Thursday with
weak waves of low pressure moving along it. High pressure should
start to build back in Friday and last through the weekend.
Near term /until 6 am Monday morning/...
minor changes made...mainly to hourly temperatures and dewpoints for the
next few hours. Forecast otherwise on track.
Hi pressure will bring light wind flow across the region
tonight...allowing for some patchy fog development late. Subsidence
and sunset will allow for the cumulus to dissipate. Satellite indicates that
the residual cirrus is also dissipating...so the forecast for tonight is
mainly clear. A blend of the guidance was used for temperatures.
Short term /6 am Monday morning through Monday night/...
the sprawling hi sets up offshore through the period...resulting in
steady onshore flow. Dewpoints will respond by rising to near 70
by Tuesday morning. Although some surface based instability develops during
the day...subsidence and an increasingly stable marine layer
should serve to inhibit convection. Left the forecast dry as a result.
Increasing thetae may support an isolated shower or thunderstorm Monday night
however...particularly western zones. Lift supplied by a relatively
weak 25-30kt lljet. Fog possible with the rising
humidity...although the increasing middle level moisture may limit
development. As a result maintained only patchy for now. Temperatures a
blend of the guidance which was in good agreement.
There is a moderate risk for rip current development Monday at the
Long term /Tuesday through Sunday/...
a trough of low pressure shifts in vicinity of the western zones Tuesday and
remains there through the night. Chance of showers and thunderstorms Tuesday
with increasing instability and moisture convergence. Better chances
will be generally over the northwest half of the County Warning Area. Mav/NAM MOS for high
temperatures were similar and a blend was used...but they still might be a
couple of degrees too low...especially if fewer clouds materialize
A cold front then moves in from the northwest Wednesday afternoon and
probably clears the eastern zones by midnight. Will cap probability of precipitation at high
end chance Wednesday/Wednesday night as NAM and CMC imply chance coverage at
best...but will at least go with scattered wording. Probability of precipitation for this period
might eventually need to be bumped up should NAM and CMC come into
better agreement with the wetter GFS and European model (ecmwf). Enough cape is
present for a chance of thunderstorms...and with high precipitable
water values...fairly light steering flow...and the cold front
becoming more aligned with this steering flow aloft...there a
concern for heavy rain and training of cells storms that could lead
to least minor urban/small stream flooding.
Higher confidence now that the cold front will stall south of the
County Warning Area on Thursday...but not by much. A weak wave of low pressure then
travels west along this boundary. Timing of its passage to our south
still a little uncertain...but it's trending towards Friday morning.
Will still leave in slight chance probability of precipitation for Thursday between the
uncertainty of this timing and to account for any chance that the
stalled boundary ends up farther north than currently prognosticated. But
right now Thursday would shape up to be a dry day. Will then
continue with slight chance probability of precipitation in the grids for Thursday night and
Friday morning for now. Thereafter...dry weather forecast as weak
high pressure builds back in.
Aviation /00z Monday through Friday/...
high pressure over the terminal this evening drifts offshore
tonight. The high remains nearly stationary off the coast through
VFR. Patchy fog develops across outlying terminals late tonight
with MVFR visibilities likely. Brief IFR visibilities and/or ceilings
will be possible at khpn...kgon...and kswf. Conditions improve to
VFR early Monday morning.
Wind generally light and variable tonight...with a light southwest
flow at the NYC area terminals. Sea breezes develop at the terminals
Monday...with the exception of kswf.
Outlook for 00z Tuesday through Friday...
Monday night...MVFR/IFR conds likely in fog stratus.
Tuesday...mainly VFR. Chance thunderstorms...especially western areas. S winds.
Tuesday night...MVFR/IFR conds likely in fog.
Wednesday...mainly VFR with a chance of thunderstorms. SW winds.
Thursday/Thursday night...MVFR possible with a chance of showers. Flow
Friday...mainly VFR. A chance of showers.
hi pressure will keep winds and seas blw Small Craft Advisory levels through Monday night. A
trough of low pressure approaches on Tuesday...then a cold front
approaches on Wednesday and stalls just south of the waters on
Thursday. This could tighten the pressure gradient somewhat
Tuesday and Wednesday...but winds and seas are expected to remain
below advisory criteria. It could come close to reaching criteria
thresholds however on the ocean waters Tuesday afternoon and
evening. Then with the front settling nearby Thursday...winds and
seas should diminish.
significant precipitation could occur at some point during middle week.
Tuesday and Wednesday both offer potential for at least localized urban and
poor drainage flooding with generally weak steering flow. The
greater potential appears to be Wednesday night into Wednesday
evening. Will continue to highlight this in the severe weather potential statement.