Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
348 am EDT Sat Aug 2 2014
a frontal boundary over the Atlantic coast and low pressure
traveling along it impacts the area this weekend. Weak high pressure
will then be in place for Monday and Tuesday. A cold front
approaches late in the day Tuesday before passing through Tuesday
night into Wednesday. High pressure then follows for the rest of the
Near term /until 6 PM this evening/...
wave of low pressure moves NE along a stalled boundary just
offshore. Forcing associated with this wave brings the likelihood of
rainfall...focused more over around the city and points east. Leaned
towards a GFS/European model (ecmwf) blend for rain amounts based on what has been
observed upstream. 00z NAM is too slow with its quantitative precipitation forecast.
Not expecting as much coverage of rain by mid-afternoon...but the
proximity of the frontal boundary plus a weak middle level shortwave in
the vicinity warrant at least slight chance to chance probability of precipitation during the middle
and late afternoon hours. Cape is limited and elevated...so it looks
like there could be in isolated thunderstorm offshore...closer to
center of low pressure and better upward forcing.
Looks like rain amounts will fall below flash flood guidance. Parts
of NE New Jersey will need to be watched more closely this morning as flash
flooding is not entirely impossible. See the hydrology section below
for more details.
Clouds...rainfall...and onshore flow will hold high temperatures
below normal levels.
Short term /6 PM this evening through Sunday night/...
a shortwave weakens at the base of a 500mb trough axis as it
approaches the forecast area...eventually entering the region late
Sunday night. This will help slowly nudge the offshore frontal
boundary farther out to sea. Still not too much coverage of rainfall
during the evening hours of tonight...but another weak wave of low
pressure forms and moves north along the frontal boundary. This will
bring likely probability of precipitation offshore and to parts of Long Island late at night
and Sunday morning. Slight chance to chance probability of precipitation elsewhere. Probability of precipitation
then lower across the island Sunday afternoon as the frontal
boundary drifts farther away. Highs on Sunday remaining below normal.
For Sunday night...the shortwave and upper trough axis move
in...however with a lack of significant cape and a drying
atmospheric column. There could be an isolated shower far northwest with
this...otherwise it looks like a dry night outside of any showers
that brush the far southeast portions of the area associated with the
Long term /Monday through Friday/...
shortwave and trough axis aloft exits to the east Monday
morning...pushing both middle level lift and the surface boundary lift
and moisture convergence farther out to sea. Still...some synoptic
upper divergence and lift present as the entrance region of a jet
streak remains over US. Additionally...a decent amount of cape builds
inland during the afternoon. So with a weak cap forecast and still
the possibility of a weak middle level shortwave passing through. Will
leave at least isolated probability of precipitation over some of the inland areas.
Directional and speed shear will be weak...so slow-moving pulse-type
storms would be expected. High temperatures on Monday near normal. We
stabilize Monday night with the loss of daytime heating...so with
weak high pressure...dry weather expected during the overnight hours.
For Tuesday...a cyclonic flow begins to develop aloft...and a
pre-frontal trough develops over the western part of the forecast
area...or at least close to it. Cross-sections reveal a lack of
moisture during this time...but possibly just enough over the far northwest
portion for an isolated shower or thunderstorm. A trailing cold
front eventually moves through...with models in decent agreement
that it will be positioned close to or over Long Island by Wednesday
morning. Will therefore carry isolated probability of precipitation across the area. The flow
aloft becomes more cyclonic with a strengthening cold pool. Models
showing sufficient moisture to keep a isolated probability of precipitation in during the day.
Highs for both Tuesday and Wednesday near normal.
The cold pool aloft then shifts east Wednesday night and
deep-layered ridging follows it for Thursday and Friday. Dry weather
for the period with highs near normal Thursday...and a little warmer
Aviation /08z Saturday through Wednesday/...
a frontal boundary will remain southeast of the region through the
forecast period. One wave of low pressure moves along the front
this morning...with another approaching tonight.
A period of moderate to locally heavy rain expected across NYC/New Jersey
metropolitan terminals and points east this morning with MVFR conditions.
A period of IFR conds possible across eastern terminals.
Improving conds this afternoon as rain lifts to the NE with ceilings
likely rising to VFR from west to east. Ceilings may remain MVFR across
kisp/kgon into tonight.
MVFR conds possible to return in light rain once again late
tonight. Increasing probability of this from klga/kjfk and points
Winds backing northeast this morning as the wave of low pressure
approaches.The wind will then remain from the east to northeast
through the remainder of the forecast.
Outlook for 06z Sunday through Wednesday...
late tonight...rain showers with MVFR or lower conds
possible...particularly eastern terminals.
Sun-Sun night...shra/tsra possible...MVFR or lower conds
Mon-Wed...VFR. MVFR possible in isolated rain showers/thunderstorms in the
latest guidance indicating a 6 to 8 hour period of marginal Small Craft Advisory winds
and seas this morning into afternoon on the ocean as a wave of low
pressure rides up the coast along a nearly stationary front.
Expect the gradient to weaken this evening as the wave
weakens...with winds and seas falling below Small Craft Advisory once again for tonight.
Otherwise...sub-sca conds are expected through Wednesday with a weak
gradient over the area.
rainfall amounts through Sunday morning are expected to range from
an inch to an inch and half from around the city to points east.
Locally higher amounts possible. For spots west of the city...a
quarter inch to an inch. Most of this rainfall should occur by
Rain may fall heavily briefly at times...however widespread flash
flooding is not expected. Mainly urban/poor drainage flooding is
Marine...Small Craft Advisory until 6 PM EDT this evening for anz350-