Area Forecast Discussion
Issued by NWS Upton, NY-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KOKX 202249
Area Forecast Discussion
National Weather Service New York NY
649 PM EDT Thu Apr 20 2017
A stationary front remains south of the region through Friday. A
low pressure wave slowly approaches the region tonight into
Friday, not moving across until Friday night. High pressure
builds from the north Saturday. Weak low pressure will pass to
the south Saturday night into Sunday night. Another wave of low
pressure will move off the Southeast coast on Monday, and track
slowly north through early Wednesday. High pressure builds back
across the area on Thursday.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
-- Changed Discussion --Mid/upper level trough passes across the Great Lakes region
tonight. Surface low does the same, with occluded front
tracking across PA, and Warm front approaching from the SW
Some clearing occurred earlier, but clouds will increase ahead
of the next wave of low pressure. In addition, stratus should
encroach from the SE. Upstream shower progression will need to
be watched, as they likely approach late this evening and
through the overnight. With winds turning southeast and
increasing, plus the shower coverage increasing, grounds will
become moisture laden, leading to the development of low clouds
and fog. Lows were a blend of MET and NAM12, upper 40s to lower
50s. Went a little on the cooler side with low temperatures
because of advection of the relatively cooler air over the
waters across the region.
Also, models are indicating some elevated instability moving in
with slightly negative Showalter indices. Most forcing and jet
dynamics are north of the region so not much of a forcing
mechanism to give extra strength to any showers or
thunderstorms. Will maintain slight chance. Showers and possible
thunderstorms become likely to categorical late tonight into
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.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Rain showers continue along with the fog early Friday. Fog could
be dense early along the coast. Could still have some
thunderstorms with probabilities of those being slight chance.
Rain shower chances eventually decrease Friday afternoon from
west to east as instability lowers but the forecast trend
compared to previous forecast shows a lingering of the showers
into the day and likewise a lingering of the fog across coastal
sections. That low to the west is slow to move in. The SE flow
and inversion just above the surface will keep more moisture
trapped in the low levels. The temperatures during the day
reflect this theme; a blend of the MET (2/3) and NAM12 (1/3)
with some minor adjustments yields a range of lower 50s to lower
60s for highs.
Friday night is when the low along with its occlusion will be
moving southeast of Long Island. Mainly dry weather is expected.
The winds switch to a more north to northwest flow while
remaining light. Out east towards Southeast Connecticut and
Eastern Long Island, some fog could redevelop Friday night with
residual leftover ground moisture and more onshore flow over
there. The lows were a blend of MET/MAV/ECS with minor
adjustments conveying a range of mid 40s to lower 50s.
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Unsettled weather likely for much of the weekend and into next week
as a cold front stalls south of the region on Saturday and a low
pressure system moves near the area. Latest guidance trends continue
to push the greatest precipitation further south over the weekend.
The low may meander off the coast for a couple days with high
pressure building to the north. This would result in an unsettled
weather pattern with below normal temperatures into the middle of
the week. High pressure builds back across the area on Thursday. A
southwesterly flow on Thursday will allow temperatures to bounce
back to above normal levels for this time of year.
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
A stationary front will remain to the south through Friday. Weak
low pressure and associated front will pass late tonight into
Friday morning. Showers expected overnight into early Friday
morning with patchy fog.
VFR to continue into tonight. Easterly winds becoming more SE,
generally under 10KT.
Rain arrives between 04-06Z, however it could arrive a few hours
earlier than currently forecast. Cannot rule out thunder but
confidence is too low to currently include in TAFs.
IFR ceilings return tonight with passing front and the
development of fog. Expecting fog to remain through Friday
morning which could fluctuate at times.
NY Metro Enhanced Aviation Weather Support...
Detailed information, including hourly TAF wind component forecasts,
can be found at: http:/www.weather.gov/zny/n90
KJFK TAF Comments: Timing of rain could be a few hours earlier
KLGA TAF Comments: Timing of rain could be a few hours earlier
KEWR TAF Comments: Timing of rain could be a few hours earlier
KTEB TAF Comments: Timing of rain could be a few hours earlier
KHPN TAF Comments: Timing of rain could be a few hours earlier than
KISP TAF Comments: Timing of rain could be a few hours earlier
than forecast. Vsby could be lower than forecast Friday
.OUTLOOK FOR 18Z FRIDAY THROUGH TUESDAY...
.Friday...IFR and ISO TSTM early, then improvement to MVFR in aftn.
.Friday night...MVFR in the evening, then VFR by late.
.Monday...CHC MVFR/rain in the morning, VFR in the afternoon.
-- Changed Discussion --Overall, the pressure gradient remains weak through Friday
night. Current ocean seas are between 3 to 4 feet. With winds
staying near 10 kt or less and being primarily onshore much of
the time period, these seas are expected to remain nearly
constant. Overall, sub SCA conditions are expected through
Friday night. Also with the weakness in the pressure gradient,
and more onshore flow, areas of fog develop tonight into Friday
on the water, which potentially could become dense. Eventually
expecting fog to dissipate Friday afternoon but fog could
return for at least some of the waters, mainly eastern, Friday
night. Will monitor for possible dense fog advisory overnight
into early Friday morning.
Tranquil conditions across the area waters are expected Saturday
through Monday. As high pressure remains to our north, the pressure
gradient will increase resulting in a strengthening easterly flow.
Small craft wind gusts will become likely on the ocean waters toward
Tuesday morning and continue into Tuesday evening. Wind gusts may
also approach small craft levels across the eastern Long Island
Sound and the eastern Long Island bays. With the prolonged east
flow, by late Tuesday afternoon ocean seas will likely build to
small craft levels and remain into early Wednesday morning. As high
pressure builds across the area waters later on Wednesday and into
Thursday seas and winds will drop below small craft levels.
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Rain amounts through Friday will amount to under a half inch.
However, with any thunderstorms, locally heavier rainfall
amounts will be possible. Minor flooding will be possible in
these thunderstorms especially in poor drainage and low lying
Precipitation amounts for the extended period will have no
hydrologic impacts across the hydrologic service area.