Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
155 PM EDT Wednesday Jul 30 2014
weak high pressure will remain offshore through the weekend. A weak
inland low pressure trough will develop on Thursday and remain into
Friday. A cold frontal passage is likely for the beginning of
Near term /through tonight/...
diurnally driven afternoon cumulus field...aided by a weak 500 mb
shortwave...continues to develop. Conds too dry for showers to
develop in the local County Warning Area.
Highs will top off in the upper 70s/lower 80s...close to a
GFS/NAM MOS guidance blend and consistent with mixing up to 825
Deeper middle level moisture should slowly edge into areas from NYC
north/west tonight...with mostly cloudy skies there and partly cloudy
skies to the east. Forcing for showers will be lacking as
shortwaves pivoting around a closed upper low in Ontario/Quebec
will be weak and passing just to the northwest.
Short term /Thursday/...
a better and more widespread chance for showers will come on Thursday
as a stronger shortwave pivots around the closed low...and there
may be enough instability to support an isolated thunderstorm per NAM forecast
soundings. Have scattered coverage across nearly the entire County Warning Area despite
onshore flow...as marine layer looks strong enough to inhibit
convection only across far eastern sections of Long Island and southeast CT.
Highs should once again be in the upper 70s and lower 80s.
Long term /Thursday night through Tuesday/...
the 00z model suite suggests the previous forecast was on track...so
only minor changes were made.
Instability across mainly the interior Friday will set the stage for
perhaps a few rain showers and thunderstorms. Left the low chance probability of precipitation at 30.
Maritime layer overspreads the entire County Warning Area...so thunderstorm chances appear to
drop significantly by evening...even far inland.
Subtropical tap appears likely for the weekend...however the GFS
indicates the best forcing and resultant rain chances on Sunday...
with the European model (ecmwf) on Sat. Maintained around 40 pop for the weekend...
although it does not appear it will rain all weekend at this time.
With precipitable water increasing to around 150 percent of normal...did increase
rainfall intensity to MDT.
Cold frontal passage expected on Tuesday per the 00z data...but the associated
pre-frontal trough should usher the best moisture offshore before...
possibly as early as Monday. For this reason the schc probability of precipitation on Monday
are appropriate...with a few isolated rain showers possible in the drier
air mass Tuesday afternoon.
Temperatures through the period are close to the graphical MOS...with the
previous 00z GFS ensemble guidance showing little in the way of spread
through the period.
Aviation /18z Wednesday through Monday/...
weak high pressure builds offshore through tonight.
VFR through the taf period. Could see ceilings around 5000 feet
develop by midlate Thursday morning. There is a slight chance
areas north/west of NYC could see an isolated rain showers Thursday prior to
18z...but probability of this is to low to reflect in the tafs at
Seabreeze already through kjfk/kbdr/kgon. Should push through
kisp/klga/khon this afternoon. For now expect to approach but not
move through kteb and kewr...so only back winds to SW at those
locations. Winds become light and variable/light SW again tonight.
Seabreeze should develop a tad early Thursday than it did today.
.NY 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: chnages in wind direction/speed could be off
+/- 1-2 hours.
Klga fcster comments: seabreeze timing could be off +/- 1-2 hours.
Kewr fcster comments: no seabreeze forecast...but chnages in wind
direction/speed could be off +/- 1-2 hours.
Kteb fcster comments: no seabreeze forecast...but chnages in wind
direction/speed could be off +/- 1-2 hours.
Khpn fcster comments: seabreeze timing could be off +/- 1-2 hours.
Kisp fcster comments: seabreeze timing could be off +/- 1-2 hours.
Outlook for 18z Thursday through Monday...
Thursday afternoon-Monday...VFR...excpept MVFR or lower possible
in any isolated-scattered rain showers/thunderstorms that are possible mainly in the
afternoon/evening each day.
winds and seas will remain blw Small Craft Advisory levels Friday through the weekend.
a humid air mass will be conducive to the development of heavy
showers this weekend...depending on the exact timing and track of
upper level features. Some areas of minor flooding will be possible
where these occur.