Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1029 PM EDT Wednesday Jul 29 2015
weak high pressure will slide off the middle Atlantic coast tonight.
A cold front will approach on Thursday...and move across Thursday
night. Weak high pressure will return Friday through Saturday. A
weak low pressure trough will move through Saturday night into
early Sunday...followed by another weak trough Sunday night. A
cold front will approach Monday night...and remain nearby through
Near term /until 6 am Thursday morning/...
forecast remains on track. Updated the near term grids to better
reflect trends in latest observations and model data.
Warm and muggy tonight with lows in the 70s for much of the
area although a few spots in the NYC metropolitan may struggle to fall
below 80 degrees.
Convection in parts of the middle Atlantic and central
Appalachians associated with an approaching shortwave has
largely dissipated over the last few hours. Have capped probability of precipitation at
slight chance after midnight north and west of NYC as not
expecting much in the way of activity with this shortwave...but an
isolated shower or storm cannot be ruled out before daybreak. The last
several runs of the hrrr hint at this possibility as well as the
new 00z NAM.
Short term /6 am Thursday morning through Thursday night/...
could still see isolated to widely scattered elevated convection from NYC
metropolitan north/west in the morning as the leading shortwave moves
through. Approaching cold front should bring scattered to numerous thunderstorms
from late afternoon into the evening as air mass
destabilizes...with SBCAPE up to 1000 j/kg. There should be enough
shear to support an organized line of storms or multi-cell
clusters...and given a SW low level jet up to 35 knots as forecast per NAM...these
storms have a better chance of surviving as they move past NYC
metropolitan and the lower Hudson Valley into Long Island and CT.
Stronger cells have potential to produce strong wind gusts and
dump locally heavy rainfall as precipitable water increases to just over 2 inches.
Highs on Thursday should be not quite as warm as today...generally
85-90...but with higher dewpoints maximum heat index values should
still be similar to those of today...still reaching the middle 90s
except in the higher elevations and eastern coastal sections...so
the heat advisory will continue for NYC.
There is a high risk of rip currents at ocean beaches on
Long term /Friday through Wednesday/...
long wave upper level trough will be over the northeast U.S. For
much of this time period. At the surface...a cold front will remain
just off the East Coast Friday...with weak high pressure building
in. Subsidence from this high should keep the area dry through much
of Saturday. A weak surface trough approaches late
Saturday...weakening as it does so. 12z GFS does seem more potent as
opposed to the 00z European model (ecmwf) and brings the trough through late Saturday
night with a brief period of showers and thunderstorms. Some
instability preceding the trough...so thunderstorms are possible.
However...jet dynamics look weak...though lift with the trough at
least early in the night looks decent according to the 12z GFS.
However...lift quickly weakens as the trough moves east late
Weak high pressure builds in for Sunday and Monday with a cold front
approaching Monday night. Cold front slows its approach and becomes
nearly stationary in the vicinity Monday night into Wednesday.
Again...some instability over the area as the front moves
through...mainly for eastern sections...so thunderstorms are once
again possible. Lifted indices -8 to -2 during Tuesday night...with
lift being provided by the front. Moisture is also available...with
surface dewpoints in the 60s and precipitable water ranging from 1...
they are not exceptionally high.
Aviation /03z Thursday through Monday/...
a southerly flow continues around high pressure off the middle
Atlantic coast as a cold front through the Great Lakes and into
Ohio slowly approaches. The cold front and a weak pre frontal trough
will be moving into the terminals around 18z Thursday and move
through Thursday evening. Scattered showers and thunderstorms will
accompany the front with MVFR conditions...or possibly IFR in
stronger storms. There is a higher chance of convection from the NYC
terminals and areas west. Will continue to indicate the chances with
a probability group.
Otherwise VFR until toward morning when MVFR visibilities will be
possible in fog and/or haze.
Outlook for 00z Friday through Monday...
Thursday night...scattered showers and thunderstorms ending in the
evening with MVFR conditions possible...then becoming VFR.
quiet through Thursday morning. Then as SW flow increases to 15-20 knots
with favorable fetch...ocean seas should build to 5-6 feet Thursday
afternoon and night. Low level jet passing ohd should mix to the
surface...with gusts up to 25 knots likely on the ocean and the bays of
Long Island. Small Craft Advisory issued for these hazards. Thunderstorms will also be a
hazard with a cold frontal passage Thursday afternoon/evening.
Ocean seas could build to around 5 feet Sat night into Sunday...
and again late Sunday into Monday morning. Then a more prolonged
period of 5-feet ocean seas is possible from Monday night into middle
basin average quantitative precipitation forecast of 1/2 to 3/4 inch possible in the lower Hudson
Valley and NE New Jersey...with up to 1/2 inch elsewhere. With precipitable water over 2
inches Thursday afternoon and evening...locally heavy rainfall is
possible with any stronger convection. Minor urban/poor drainage
flooding is the most likely outcome.
New York...heat advisory until 8 PM EDT Thursday for nyz072>075-176-178.
High rip current risk from 6 am EDT Thursday through Thursday
evening for nyz075-080-081-178-179.
Marine...Small Craft Advisory from 2 PM to 8 PM EDT Thursday for anz340-
Small Craft Advisory from noon Thursday to midnight EDT
Thursday night for anz355.
Small Craft Advisory from noon Thursday to 6 am EDT Friday for