Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
722 am 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. Humidity levels will also increase Friday through the
weekend due to the high offshore. A cold frontal passage is likely
for the beginning of next week.
Near term /through tonight/...
broken-overcast patches of altocu over eastern Li should gradually dissipate this
Models in closer agreement on limited moisture and low level
instability this afternoon as a weak shortwave passes...so forecast is
dry. Convective temperatures should however be reached...so expect scattered cumulus
this afternoon...possibly broken at times northwest of NYC.
Expect highs in the upper 70s/lower 80s...close to a GFS/NAM MOS
guidance blend and consistent with mixing up to 825 mb.
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 /11z Wednesday through Sunday/...
weak high pressure remains over the region.
VFR. Light and variable winds continue until sea breezes develop
this afternoon and pass through some terminals. Winds generally SW
to S 10kt or less.
Showers possible by 18z Thursday but chances too low to include in tafs
at this time.
.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: timing of sea breeze may be off by an hour in
Klga fcster comments: amendments may be necessary if NE wind occurs
earlier than forecast. Sea breeze timing may be too early by an hour
Kewr fcster comments: no sea breeze forecast but amendments may be
needed if sea breeze develops.
The afternoon kewr haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.
Kteb fcster comments: no unscheduled amendments expected.
Khpn fcster comments: no unscheduled amendments expected.
Kisp fcster comments: sea breeze timing may be off by an hour in
Outlook for 12z Thursday through Sunday...
Thursday-Friday...isolated showers/thunderstorms possible in the
afternoon/early evening. VFR outside of any showers/tstms.
Saturday-Sunday...mainly VFR...IFR conditions possible in scattered
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.