Scientific Forecaster Discussion
fxus61 kokx 291954
Area forecast discussion
National Weather Service New York New York
354 PM EDT Sat Apr 29 2017
a weak cold front will move south of the area this evening as
high pressure builds to the north. The high moves east Sunday
into Sunday night as the front returns north as a warm front. A
cold front will slowly approach from the west on Monday, and
pass by Tuesday morning. High pressure builds in briefly for
the middle of the week, then low pressure brings rain for the
end of the week.
Near term /until 6 am Sunday morning/...
mid and upper level ridging will remain across the region
through tonight as a weak surface cold front moves south of the
area. The front was just north of the cwa, across the lower
Hudson Valley and into northwestern Connecticut at mid Saturday
afternoon. With little lift, moisture, or instability with the
front, will bring through dry.
Short term /6 am Sunday morning through Sunday night/...
weak cold advection will continue through the day Sunday as the
ridge shifts to the east. Winds will back to the east and
southeast keeping the area cool. Low level moisture increases
and a low level inversion develops and strengthens through the
day. Low level clouds are expected to develop during Sunday
afternoon. High temperatures Sunday will be close to the lows
that occur Sunday morning, maybe rising a couple of degrees
early, then holding nearly steady. Did not use a diurnal trace
for temperatures for Sunday.
Stratus and fog develop Sunday night as the east flow remains.
Initially weak cold advection continues then becomes weak warm
advection after 06z as the frontal boundary to the south begins
to return as a warm front. Forcing will remain weak until
toward 12z Monday. So removed probabilities of precipitation,
and mentioned drizzle. There is a chance that showers do develop
ahead of the warm front, however, that would be more into
Monday, and across the far southern sections of the County Warning Area. If the
front move quicker, which is unlikely as the surface and upper
lows remain well to the west. Sunday night lows may occur during
the evening, then hold steady or slowly rise toward morning.
Again did not use the usual diurnal trace for hourly
temperatures Sunday night.
Long term /Monday through Saturday/...
the models were in good agreement through the extended, so the
superblend was generally used. After some residual fog and drizzle
Monday morning, a warm front is progged to lift just north of the
forecast area before stalling. It is possible that the front does
not get as far north as the models depict, but for now the model
consensus has been followed. This should allow the drizzle to cut
off across the southwestern portion of the area, with some lingering
light stuff still possible in the vicinity of the front. Chances
for showers will increase through the day as the cold front and
upper support draw closer, but the main window for rain looks to be
Monday night closer to the frontal passage. Isolated thunderstorms
have been included for this period with the enhanced lift with the
system acting on some elevated instability. Lapse rates increase on
Tuesday as cooler temperatures aloft move in. The best chance for a
stray shower will be on the northern fringe of the forecast area per
the model consensus at this time. A dry day is progged for Wednesday
with high pressure building in from the west. Chances for
overrunning light rain then increase Wednesday night ahead of
developing low pressure over the Ohio Valley. The low then tracks
through the area Thursday night and Friday, bringing moderate rain
to the tri-state region.
The temperature forecast for Monday is complicated, as the
combination of southerly flow, the exact location of the warm front,
and the influence of onshore flow will all play a part. It is
possible a 20 degree difference will set up from southwest to
northeast. Temperatures will be uniformly mild on Tuesday due to
good mixing on southwesterly flow behind the cold front. Readings
will then cool on Wednesday with the colder airmass in place. Cooler
and damp thereafter with the rain and clouds, although nighttime
temperatures will likely be above normal due to these same elements.
Aviation /20z Saturday through Thursday/...
a series of cold fronts will move through the area, one late
this afternoon, and another early this evening. These are
forecast to be dry frontal passages.
Gusty west/SW winds this afternoon will veer to the west/NW, and then
northwest to NE overnight. Gusts 20-25 kt this afternoon with the
potential for up to 30 kt. Gusts may linger into early this
VFR with scattered-broken 4-5 kft this afternoon, and then again Sunday
Outlook for 18z Sunday through Thursday...
Sunday afternoon-Monday....MVFR development late afternoon/early
evening, then widespread IFR conditions in fog/drizzle
overnight into Monday. Possible improvement to VFR Monday
Monday night...IFR or lower conditions, low level wind shear and scattered
thunderstorms are possible.
Tuesday-Wednesday...VFR. SW-west-southwest winds g15-20kt possible
Tuesday. West-northwest winds g20-25kt possible Wednesday.
Thursday...MVFR or possible in late day rain.
winds and seas are expected to remain below Small Craft Advisory
levels tonight through Sunday night. There may be a brief period
of seas near 5 feet, especially west of Fire Island Inlet,
Sunday evening as easterly winds increase.
A strong westerly flow late Saturday afternoon into the evening
may build ocean seas briefly to near 5 feet. However, seas on
the ocean waters were ranging from 3 to near 4 feet through
Saturday afternoon, below previous forecast thinking. Therefore,
the Small Craft Advisory for hazardous seas was cancelled.
Southerly winds will increase on Monday, with the ocean reaching
Small Craft Advisory criteria. The protected waters will be close to
criteria by Monday night, but all areas will reach 25 kt on Tuesday
behind a cold front. Seas will then linger above 5 ft on the ocean
through Wednesday. Winds and seas are progged to remain below Small
Craft Advisory levels on Thursday.
no hydrologic impacts are expected through the forecast period.