Scientific Forecaster Discussion
fxus61 kokx 290232
Area forecast discussion
National Weather Service New York New York
1032 PM EDT sun may 28 2017
a low pressure system approaches tonight and passes through during
Monday into Monday evening. A weak cold front approaches from
the west Tuesday, then crosses the area Tuesday night...followed
by another on Wednesday. High pressure then builds to the south
through Thursday night. Another cold front approaches on Friday
then slowly crosses the area Friday night.
Near term /until 6 am Monday morning/...
a few light rain showers are beginning to reach the ground
across parts of the area, and light rain will continue to
overspread the area tonight. Made minor adjustments to
temperatures, dew points, and winds to better account for
current trends, otherwise the forecast remains on track.
Otherwise...a primary low pressure center slowly shifts
eastward just north of the Great Lakes. An associated occluded
front drifts towards US, and models are in general agreement
that a secondary weak low pressure center forms along the front
to our south before emerging off the mid-Atlantic coast. Trends
have been for a more defined secondary low, but there is still
disagreement on the northern extent of its eventual track and
associated lift. Between shortwave and isentropic lift, and
synoptic lift from an approaching jet streak, thinking is that
the likelihood of rainfall is still there by late tonight for
the city and areas west of the Hudson. Patchy fog is expected as
well with this being the 2nd night in a row with a southeast flow.
Short term /6 am Monday morning through Monday night/...
the secondary low center remains to our south Monday morning as it
shifts out of the picture in the afternoon. Meanwhile, the occluded
front begins to move through the forecast area during Monday
afternoon and exits to the east during the evening. Additional lift
will still be present with jet streak dynamics and shortwave energy.
Rain is therefore expected across the entire tri-state area for the
morning at least through the morning. For at least the city and west
of the Hudson, much of the afternoon could be still be dry although
breaks of sunshine will probably be limited. The threat of rain
doesn't exit east until around sunset, but any rainfall after mid-
afternoon would probably be east of the city. Clouds and rain will
limit high temps to only around 60. West of the Hudson is forecast
to be mostly in the lower 60s, but even upper 60s can happen there
if clouds break up more quickly than currently forecast.
As for thunder, can't rule any out with a few hundred j/kg of MUCAPE
forecast, but this would be an isolated occurrence in during the
morning/midday hours. Rain amounts are expected to average around a
half of an inch.
A weak high pressure ridge axis will stretch into the region during
the nighttime hours. With low level moisture leftover from the rain
and light to calm winds, expecting stratus and at least patchy fog
during the overnight hours.
Long term /Tuesday through Sunday/...
global models remain in good agreement through Fri with an
amplified 500 mb pattern across North America. Differences then
emerge from Fri night through the weekend with the upper
pattern...specifically how quickly the upper low over eastern
Canada tracks ewd across the Maritimes and nrn New England.
Additionally...there are differences with the interaction of
energy aloft associated with the next system that may impact the
area next weekend.
Tue through Fri...a closed upper level low over Ontario will
slowly track ewd through the week due to a downstream Omega
block. A series of shortwaves and sfc fronts/troughs will move
across the area during this time...bringing the chances for
showers and tstms each day except Thu. Tue is expected to start
out with fog and stratus with a light onshore flow. Some
question on how thick and widespread the fog will be with the
cloud cover...so have only included patchy fog in the morning
for now. Soundings are indicating stratus or stratocu remains
around for much of the day which makes high temps a challenge.
Think there could be some breaks during the aftn...so leaned
towards the higher temp guidance.
A cold front approaching from the west will move across the area
Tue night. There could be a few isold shra/tstms in western
areas...especially late in the day. Chances for showers increase
overnight as a weak wave of low pres develops along the
boundary. Instability wanes with the loss of heating so have
removed tstms after midnight.
The next shortwave/weak cold front approaches on Wed and moves
through Wed aftn/eve. Less available moisture...thus low chc
pops with its passage.
High pres builds to the S Thu with no discernible shortwaves
moving around the low aloft. Thus...Thu/Thu night should be dry
with mostly clear skies.
As the low finally tracks through the Maritimes and nrn New
England on Fri another cold front will move across the area. Sct
aftn convection is a possibility...although instability appears
Front clears by Sat morning although this is where uncertainty
aloft begins. Models currently agree that an approaching
shortwave will impact the area Sat night into sun...but they
don't agree on the details on timing on precip and strength of
developing low over the Ohio Valley.
Aviation /02z Monday through Friday/...
a frontal system will approach late tonight...and cross the
area on Monday.
Rain will overspread the region over the next few hours, however
expecting MVFR conditions to arrive after midnight. Further
deteriorating conditions to IFR heading into the morning
push...with low prob for sparse thunderstorms and rain as well.
Winds turn easterly and increase for coastal terminals to
around 14 kt with gusts to 20 kt late tonight and continue
through Monday morning as a wave of low pressure tracks to the
Outlook for 00z Tuesday through Friday...
Monday night...MVFR or lower conds possible in stratus.
Tuesday...MVFR or lower to start...possibly improving to VFR in
the afternoon. Chance of aft/eve showers and possibly a tstm.
MVFR or lower possible Tue night.
Wednesday...VFR. Chance of aft/eve showers/tstms mainly northwest of
the NYC Metro terminals.
Friday...VFR. Aft/eve showers/tstms possible.
winds and seas increase during the late night hours of tonight in
response to low pressure emerging off the mid-Atlantic coast and
passing to the south of the area waters. Have gone with a Small Craft Advisory on the
ocean from midnight tonight through Monday afternoon. There could be
a gust or two to 25 kt on the other waters late tonight into Monday
night, but not Worth expanding the Small Craft Advisory to these areas. Winds and
seas then remain below advisory criteria Monday night as a high
pressure ridge axis stretches in from the northeast.
Sub-advsy conds continue through the remainder of the forecast
period. If winds on Fri end up being a little stronger than
forecast seas could build to 5 ft on the ocean waters.
no hydrologic impacts are expected with the rainfall late tonight
into Monday. There is a slight chance of a thunderstorm during
Monday morning/early afternoon, but only a low chance of minor
urbanized flooding would occur with any thunderstorms.
No significant widespread hydrologic impacts are then expected
at this time from Monday night through at least Thursday night.
while astronomical tides are a little lower for the high tide cycle
tonight, surge will increase a bit due to southeast flow.
As a result, a coastal flood advisory continues for the South
Shore bays of Brooklyn, Queens, and Nassau, where widespread
minor coastal flooding is expected. Elsewhere, brief/localized
minor flooding is possible along the shores of Westchester/Fairfield
western Long Island Sound, SW Suffolk, and along the kill Van kull
and Arthur kill around Staten Island and adjacent portions of New Jersey.
Additional minor coastal flooding may occur with the high tide cycle
Monday night...mainly for the southern bays of Nassau/NYC.
New York...coastal flood advisory until 3 am EDT Monday for nyz075-178-
Marine...Small Craft Advisory until 6 PM EDT Monday for anz350-353-355.