Scientific Forecaster Discussion
fxus61 kokx 220234
Area forecast discussion
National Weather Service New York New York
1034 PM EDT Thu Jun 21 2018
a weak cold front will dissipate over the region this evening
with high pressure building north of the area. The high lifts
to the north and east on Friday as a frontal system approaches
from the southwest. A warm front passes late Saturday into
Saturday night and will be followed by cold fronts on Sunday and
then on Monday. High pressure returns for Tuesday and
Near term /until 6 am Friday morning/...
a cold front dissipates over the area tonight. Weak cold
advection and the upper trough passing through the northeast
will allow high pressure to build to the north of the area
tonight. This will allow a light S/southeast flow gradually to back to
Stratus/patchy fog deck along east Li/southeast CT will continue to drift
westward across much of east Li/southeast CT through midnight in easterly
flow ahead of weak cold front. Expectation is this should begin
to get suppressed offshore late tonight into Fri morning as flow
becomes NE and drier air advects south as cold front
dissipates. Fog could be locally dense along the immediate
shoreline at times.
Overnight lows will be nearly seasonable ranging from the upper
50s across the interior, to the mid and upper 60s across the
Short term /6 am Friday morning through Friday night/...
upper trough lifts out across the northeast on Friday, while
heights build ahead of an upper low lifting northeast into the
Ohio Valley. This will send a warm front northward along the
mid Atlantic coast as high pressure centered over northern New
England moves out into the western Atlantic.
Overrunning mid and upper level clouds will increase through
the day with a strengthening easterly flow between the departing
high and associated warm front to the south. Gusts up to 20 mph
will be possible, especially near the coast.
Additionally, a frontal wave along the warm front passes off to
the south and east of the area Friday night. This in turn may
strengthen the low-level ridging across the area enough to
maintain dry air. There have been multiple scenarios playing
out in the guidance the last several days with the potential for
rainfall Friday night, but latest indications are that the rain
will arrive late and should be mainly light. Also, the upper
low is weakening and opening up as it runs into the ridge over
the western Atlantic. Should the frontal wave be a little father
west than forecast, this would pose the potential for steadier
rain across eastern Long Island. There is low confidence in this
More or less this will be an easterly flow event with some
light rain and cooler temperatures. Highs on Friday will be in
the 70s, with lows in the upper 50s to lower 60s.
Long term /Saturday through Thursday/...
upper low will continue to open up and flatten through the day on
Saturday as it moves across the Great Lakes region. The flattening
shortwave will continue to traverse across New England on Sunday.
The main upper flow over the northeast this weekend into next week
Closed upper low opens as it traverses across the Great Lakes region
and into New England this weekend. Another shortwave in a broader
cyclonic flow regime aloft will pass on Monday. Upper ridging
returns for Tuesday into Wednesday with the next possible shortwave
for next Thursday.
There has not been too much change in the overall thinking for
sensible weather. There are still differences in the model guidance
with the depth of surface ridging and the exact direction of the
surface winds. The NAM on Saturday has northeast flow at the surface
and the GFS is more easterly. The NAM depicts a weak surface wave
moving off the south and east on Saturday and the GFS has less of a
reflection of a surface wave. This will make a big difference in low
level moisture and the potential advection of drier dew points from
the northeast into the region. Confidence in higher pops has lowered
and therefore have lowered them until the evening hours. Saturday
may just remain overcast with some light rain at times, with better
forcing and moisture arriving in the evening as the warm front and
shortwave axis nears the region. The shortwave axis lifts up into
northern New England after 06z, which will end any showers.
Instability is weak Saturday night, so will just mention slight
chance of thunder.
Westerly flow aloft will dry the middle and upper levels out enough
for a return to partly cloudy condition on Sunday. A trailing cold
front approaches late in the day along with some trailing shortwave
energy. A chance for showers and thunderstorms is supported by these
systems in the afternoon and evening. A much sharper upper level
trough approaches late Sunday night into Monday with a secondary
cold front ahead of it. The GFS is much stronger with the embedded
energy within the trough which agrees with the CMC. The European model (ecmwf) is
much broader and faster with the trough. Low pops will persist into
Monday for a continued chance of showers.
High pressure returns for Tuesday into Wednesday with the next cold
front approaching on Thursday. Temperatures should then average near
normal for next week.
Aviation /03z Friday through Tuesday/...
high pressure builds in from the north overnight and moves off
the northeast coast Friday.
Meanwhile another frontal boundary will remain well to the
south, through the mid Atlantic region and off the coast. A wave
of low pressure will approach from the west late in the
Stratus and fog, with IFR to LIFR conditions have been
developing across coastal CT and eastern Long Island. With a
light northeast flow overnight the stratus will likely move
into the NYC Metro terminals before sunrise Friday, with IFR
conditions for several hours. Conditions improve to VFR 12z to
15z. There is uncertainty as to how long the stratus and fog
will remain overnight as high pressure will be building in from
the north with drier air moving into the region.
Winds will be light, under 10 knots from the NE to east overnight.
Winds then increase from the east to southeast, 10-15, Friday
morning, and then remain into the afternoon. Occasional gusts to
near 20 knots are possible during Friday afternoon.
Outlook for 00z Saturday through Tuesday...
Friday night...VFR early, then becoming MVFR with a chance of
Saturday...sub-VFR. Showers likely, possibly a thunderstorm
during the evening and nighttime hours.
Sunday...chance of sub-VFR conditions in showers and
Monday...chance of showers early, becoming VFR.
dense fog advisory continues for ocean and eastern nearshore
waters tonight as stratus/fog deck advects over the waters.
This stratus deck should eventually get suppressed south mainly
over the ocean late tonight into Friday morning.
A strengthening easterly flow late tonight into Friday will
result in building seas and the potential for marginal Small Craft Advisory
conditions on the ocean waters Friday into Friday night.
Preference at this times was to hold off on any issuance.
Winds will likely stay below 25 kt Saturday through early next
week. Winds on the ocean may approach 20 kt at times this
weekend, but will otherwise stay below 25 kt through early next
Ocean seas may build to 5 ft this weekend as a warm front moves
north and SW flow increases. Ocean seas may also approach 5 ft on
Monday with seas otherwise remaining below Small Craft Advisory levels on Tuesday.
some light rain is possible Friday night into Saturday.
There could be a few locally heavy downpours on Saturday night
and Sunday, but no hydrologic impacts are anticipated this
NYC National oceanic and atmospheric administration weather radio station kwo-35 (162.55 mhz) remains off
the air for an extended period of time.
Marine...dense fog advisory until 8 am EDT Friday for anz330-340-345-