Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1109 PM EDT Monday Apr 20 2015
a wave of low pressure will move across the region overnight.
Weak high pressure will follow for Tuesday. A cold front will pass
on Wednesday...allowing for a cool air mass to settle in late this
week into the weekend.
Near term /until 6 am Tuesday morning/...
stationary front remains draped from central New Jersey to just south of
NYC to across Long Island as of 03z...with a triple point low near
York PA and Westminster Maryland. Watching lines of thunderstorms to the west
and southwest...one over eastern PA and another cluster over southeast PA and
northern Delaware-Maryland-Virginia. With MUCAPE 500-750 j/kg to the west...the first may
survive into Orange and western Passaic counties and produce brief
heavy rain and small hail before wakening on approach toward NYC.
The cluster over southeast PA may survive longer via better
lift/convergence on nose of low level jet ahead of the triple point
low...and impact Long Island and southeast CT overnight.
Expanded dense fog advisory to all of NYC and NE based on latest observation
and guidance which continue to lower visibilities overnight. The dense
fog will likely dissipate with the showers overnight.
Temperatures should remain mostly steady overnight...but could rise late
across eastern Long Island ahead of the triple point low.
Short term /6 am Tuesday morning through Tuesday night/...
shortwave is forecast to move through in the morning with
stronger lift generally over the northern zones. Have kept a
chance for showers in there. Otherwise...turning partly to mostly
sunny. Highs are a MOS blend.
Long term /Wednesday through Monday/...
500 mb low currently spinning over Minnesota/WI will slowly track eastward through
the week...then stall over Quebec and northern ME this weekend.
The approaching 300 mb jet on Wednesday appears it should produce enough
upper divergence to allow for the development of showers. In
addition...there should be some low level convergence as the associated
cold front tracks through. As a result...indicated scattered showers in the forecast.
As this system slides offshore Wednesday night...the precipitation ends and the
remainder of the forecast period is dominated by cyclonic flow aloft
and marginal middle level lapse rates. The steepest lapse rates will be north
of the County Warning Area across northern New England. Will therefore forecast fair weather
Thu-Mon. Scattered-broken clouds...especially during the day...as temperatures hit
convective which is prognosticated to be in the upper 40s to 50s per GFS
bufr data. There could even be periods of overcast skies as the cumulus
flattens due to decent shear. Cant rule out some isolated
sprinkles...but the probability is too low at this time to include in the forecast.
Temperatures a blend of guidance and generally blw climatology through the
extended. Highs could be a little warmer than forecast on Wednesday
depending on the amount of cloud cover and speed of the developing
showers ahead of the front.
Aviation /03z Tuesday through Saturday/...
a warm front will remain just south of the area for much of the
overnight and may push into coastal areas late before a cold
frontal 09z-13z. This will result in widespread LIFR conditions
prior to frontal passage with a light easterly flow.
Showers west/isolated thunderstorms and rain possible 05z to 09z...from west to east.
Activity is likely to weaken as it works in the area.
VFR with a gusty west flow on Tuesday. Gust up to 25 knots possible.
Outlook for 00z Tuesday through Saturday...
Wednesday-Wednesday night...MVFR possible in the afternoon and
night in -shra. SW-west-southwest winds g20-25kt possible.
Thursday-Friday...mainly VFR...with low chance MVFR in any
-shra. West-northwest winds g15-20kt possible.
dense fog advisories now in effect on all waters for visibility below 1 nm
in marine fog. Seas remain elevated on the ocean through at least
West flow for Tuesday mainly below Small Craft Advisory...but there could be a few
afternoon near-shore gusts to 25 knots especially the waters in vicinity of
NYC and the Long Island South Shore.
Winds and seas will be close to Small Craft Advisory levels Wednesday through the weekend.
The best chances for reaching criteria will be on the ocean Wednesday-Thursday
in vicinity of a cold front.
heavier showers/thunderstorms could produce localized 1/2 to 1 inch
rainfall amts overnight...mainly in Orange/west Passaic and also
across eastern Long Island and coastal southeast CT. Otherwise...areal quantitative precipitation forecast is
less than 1/4 inch overnight.
Around a quarter inch of rain is possible on Wednesday as a cold front tracks
through the hsa.
CT...dense fog advisory until 6 am EDT Tuesday for ctz005-006-
New York...dense fog advisory until 6 am EDT Tuesday for nyz067>075-
New Jersey...dense fog advisory until 6 am EDT Tuesday for njz002-004-006-
Marine...dense fog advisory until 6 am EDT Tuesday for anz330-335-338-
Small Craft Advisory until 6 PM EDT Tuesday for anz350-353-355.