Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
329 PM EDT sun Sep 21 2014
a cold front approaches from the west early this evening...then
crosses the tri-state the remainder of the night...meanwhile a
coastal low tracks to the east...then northeast of Long Island
tonight. High pressure then builds in from the west through
Tuesday. The high then dominates the weather through next Sunday.
Near term /until 6 am Monday morning/...
700-500 hpa trough approaches this evening then begins to cross
the tri-state overnight. Radar trends and all guidance suggests
that any -shra ahead of it and its associated cold front will be
falling apart as they approach the County Warning Area. This is due to loss of
thermodynamic forcing after sunset and best dynamics staying to
the NW/N. So for now have chance probability of precipitation over far West Orange County
towards middle evening...with slight chance probability of precipitation over most of the
remainder of the northern tier. For now believe probability of
measurable precipitation is less than 15 percent across southern
zones...so have gone with a dry forecast there - however a stray
shower or two/sprinkle cannot be completely ruled out.
For lows tonight sued a blend of mav/met guidance with values
forecast to be 4 to 8 degrees above normal outside of the NYC heat
island...and near normal inside the heat island and areas to the
north/west of NYC due to the timing of the cold front.
Also have the potential for patchy fog this evening over southeast CT/the
Twin Forks ahead of the cold front. While locally dense fog cannot
be ruled out - am currently not confident enough in its potential
to issue any statements.
There is a moderate risk of rip currents at Atlantic beaches this
Short term /6 am Monday morning through Monday night/...
region remains under the base of 700-500 hpa trough Monday and
Monday night. Will have a few shortwaves round the base of the
trough - but given forecast drying in the low levels would only
expect at most some clouds as they pass. So going with a mostly
sunny to partly cloudy sky Monday and a mostly clear to clear sky
Monday night as a result.
For highs Monday used a blend of mixing down from 875 hpa...except
850 hpa over the northwest 1/4 of the County Warning Area per BUFKIT soundings...with NAM
2-meter temperatures and a blend of mav/met guidance. Expect
readings to be near to slightly below normal.
A blend of mav/met guidance was used for lows Monday night - with
readings forecast to be 5-10 degrees below normal. Lows in the upper
30s are possible in portions of Orange County.
Long term /Tuesday through Saturday/...
a strong upper ridge will be building into the East Coast Tuesday
and Tuesday night...then remain nearly stationary through Sunday.
At the surface high pressure builds east from the Ohio Valley while
another surface high builds in from central Canada. The combined
high pressure center will build east from the Great Lakes and
through northern New England Tuesday into Wednesday. The high then
builds over the region Thursday and remains nearly stationary into
Sunday. Initially the air mass will be cool Tuesday into
Thursday...with slightly below seasonal normal temperatures. A
warming trend sets up for Thursday night through Sunday as the air
mass modifies. Next weekend temperatures will have rebounded to
above seasonal normals.
Aviation /19z Sunday through Friday/...
weak low pressure will pass to the southeast this afternoon and evening.
A cold front will approach this evening and pass through late
tonight...followed by building high pressure on Monday.
IFR ceilings associated with onshore flow just ahead of the offshore
low have moved back in at kisp/kgon...and are likely to remain
tonight until cold frontal passage...though they may improve to MVFR for a
couple of hours before frontal passage late tonight.
Elsewhere...MVFR ceilings elsewhere may briefly improve to VFR late
this afternoon...but with nighttime cooling expect at least tempo
MVFR ceilings to return toward evening for 2-3 hours before cold frontal passage.
Timing of frontal passage looks to be 05z kswf...05z-06z NYC metropolitan...and
07z-08z farther east...with quick improvement to VFR.
West-northwest winds...west of 310 magnetic...at 10-15 knots with gusts around
or just over 20 knots...should develop by 12z Monday. Gusts could start
a couple hours sooner than forecast...and could briefly touch 25 knots in
NYC metropolitan between 12z-15z.
Outlook for 18z Monday through Thursday...
Monday afternoon/night...VFR. Northwest winds g20kt into early evening.
seas build to up to 5 feet on the western coastal ocean waters and
up to 8 feet on the eastern coastal ocean waters by late tonight.
With wind gusts up to 25 knots on the coastal ocean waters on Monday
- have converted Small Craft Advisory for hazardous seas to a plain Small Craft
Advisory. Small Craft Advisory wind gusts should linger over the eastern two
coastal water zones into Monday evening and Small Craft Advisory level seas through
the night in those two zones...so have extended the Small Craft Advisory for
anz-350 and 353 through 10z Tuesday as a result.
On the remainder of the coastal ocean waters sub-Small Craft Advisory conditions are
currently expected through Monday night. Wind gusts to 20 knots are
forecast on Monday - however occasional gusts to 25kt cannot be
There is a chance of lingering 5 foot seas across the extreme outer
ocean waters east of Moriches Inlet very early Tuesday morning as
seas will be subsiding as high pressure builds in.
With high pressure across the waters Tuesday into Saturday wind and
seas are expected to remain below Small Craft Advisory levels.
little if any additional rainfall is expected through tonight with
the passing of a coastal low to the east and the passage of a
It should then be dry from Monday through next Sunday.
Marine...Small Craft Advisory from 6 PM this evening to 6 PM EDT Monday
Small Craft Advisory from 6 PM this evening to 6 am EDT
Tuesday for anz350-353.