Scientific Forecaster Discussion
fxus61 kokx 202000
Area forecast discussion
National Weather Service New York New York
400 PM EDT Fri Oct 20 2017
high pressure builds across the area before gradually shifting
offshore by late weekend. High pressure continues to move
offshore going into Monday and Monday night. A strong cold
approaches on Tuesday and moves across by early Wednesday. The
front slows down its eastward progress, staying close to the
region Wednesday into Thursday as weak low pressure develops
along the front. The front moves farther east away from the
region later Thursday into next Friday with weak high pressure
returning to the region.
Near term /through tonight/...
subtle downslope northwest flow has allowed deeper mixing across
the urban areas in and around NYC, leading to dry conditions
detailed in the fire weather section. Overall, gusty winds
should gradually decrease through the evening as high pressure
builds in and the pressure gradient begins to relax. Nary a
cloud in sight amidst high pressure, which will create favorable
radiational cooling conditions tonight as winds subside. Despite
radiational cooling, above normal temperatures will continue
with lows in the 40s across most areas and closer to the low to
mid 50s in urban areas and closer to the coast.
Short term /Saturday through Saturday night/...
high pressure continues into Saturday with a subtle return
flow/weak warm air advection allowing unseasonable warmth. Highs will generally
be in the 70s, and may approach 80 degrees in northern New Jersey. Skies
will remain clear into the night, once again allowing
radiational cooling as winds relax. Temperatures and moisture
will be slightly higher than Friday night in a light onshore
Long term /Sunday through Friday/...
the jet stream will remain well north of the region with upper
level ridging Sunday through Monday. Clouds will be minimal
until Monday when an upper level trough will dig to the west of
the region and become amplified. There will be an increase in
meridional flow across the region. At the surface, high pressure
continues to move offshore during this period, increasing warm
and moist air advection.
Low levels look to become moist enough late Monday night into
early Tuesday for the development of patchy fog. The upper level
trough and jet stream dive toward the southeast during this
time. The meridional flow increases further across the region.
For Tuesday, rain showers will expand and develop ahead of the
cold front. The southerly flow will increase to near 20 to 25
mph with higher gusts to near 30 to 35 mph possible. The
precipitable waters grow to near 1.8 inches according to the
GFS, which is slightly higher than what this model was showing
yesterday. This would be well above the 90th percentile
according to okx sounding climatology. With parallel flow from
low to high levels, training of showers and thunderstorms will
be possible with potential for heavy rain. The thunderstorms are
only a slight chance with surface cape only a few hundred j/kg
so expecting these to materialize as a few embedded
thunderstorms within the heavy showers.
The cold front moves across Wednesday morning, with a
substantial decrease in precipitable water thereafter to much
below 1 inch. The front slows down and is slow to depart away
from the region. The numerical forecast models show weak low
pressure development along it approaching the region Wednesday
into Thursday, with rain shower chances continuing, highest for
southeast CT and eastern Long Island.
Chances for rain showers lower Thursday into Friday as the front
pushes farther east of the region. Did not trend down too fast
in case subsequent model runs are stronger with the low along
the front and trend closer to the region with the front. Weak
high pressure moves in Thursday into Friday next week.
Temperatures are expected to be well above normal Sunday through
Tuesday with a little decline thereafter to values closer to
normal. Highs Sunday through Tuesday are forecast to be well
into the 70s with lows trending to be well into the 50s to
lower 60s for some locations along the coast and NYC. The highs
are forecast to be more in the 60s for Wednesday through Friday
Aviation /18z Friday through Wednesday/...
VFR through the taf period as high pressure builds in from the
west through tonight, then begins to move offshore Saturday.
Good confidence in the wind forecast with the typical 20
degrees of variability either side of forecast through the day.
Gusts continue up to around 20 kt, with the gusts becoming more
occasional after 20z with the gusts expected to end around 22z.
Winds become light and variable to near calm tonight. Saturday
morning a S to SW light flow develops.
New York Metro enhanced aviation weather support...
Detailed information, including hourly taf wind component fcsts,
can be found at:
Kjfk taf comments: no unscheduled amendments expected.
Klga taf comments: no unscheduled amendments expected.
Kteb taf comments: no unscheduled amendments expected.
Khpn taf comments: no unscheduled amendments expected.
Kisp taf comments: no unscheduled amendments expected.
Outlook for 18z Saturday through Wednesday...
Tuesday...MVFR possible in showers. S wind g20-25 knots at coast.
Low level wind shear possible.
Wednesday...VFR. A chance of showers with areas of MVFR,
a few gusts to near 20 kt will be possible on the waters through
this evening in northwest flow. Otherwise, high pressure builds
across the area then slowly shifts offshore by late weekend,
maintaining tranquil conditions across the waters. Conditions
stay below Small Craft Advisory Monday into Monday night. Then southerly flow and
fetch increase ahead of the cold front Tuesday. Small Craft Advisory conditions
more probable for all waters Tuesday into Tuesday night,
lingering for the ocean Wednesday into Wednesday night with non-
ocean waters trending below Small Craft Advisory as cold front lingers offshore.
a Special Weather Statement remains in effect through 6 PM
tonight for the entire region due to enhanced fire danger.
Minimum relative humidity values have fallen to mid 20 to near 30 percent,
except in the New York/New Jersey Metro areas where values have fallen into
the upper teens to lower 20s. Occasional gusts to near 20 mph
are expected through the early evening before gradually
no hydrologic problems are expected through Monday night. For
Tuesday through early Wednesday, heavy rain will be possible at
times with potential areas of 1 inch or higher. There is much
uncertainty with exact rainfall amounts. Urban and poor drainage
flooding will be possible.