Scientific Forecaster Discussion
fxus61 kokx 281629
Area forecast discussion
National Weather Service New York New York
1229 PM EDT sun may 28 2017
high pressure gradually retreats to the northeast as a series of
weak lows track to the south of Long Island through Tuesday. A
weak cold front approaches from the west Tuesday night, then
crosses the area Wednesday. High pressure then builds in to the
south and southwest through Thursday night. A cold front
approaches on Friday then slowly crosses the area Friday night
Near term /until 6 PM this evening/...
an upper ridge axis moves through the region today with weak
high pressure at the surface.
The forecast is mostly on track. Only minor adjustments to
temps/dewpoints/sky cover based on the latest trends. Still
partly sunny with sun filtered through cirrus for most spots,
but thicker cumulus and mostly cloudy for interior sections.
Short term /6 PM this evening through 6 PM Monday/...
the northern stream ridging slides offshore tonight, delaying
the onset of light rain (in response to increasing isentropic
lift) until mainly after midnight.
A northern stream shortwave pushes through the area Monday.
Along with it are some fairly steep mid level lapse rates,
reflected with showalters progged down to around -2 and possibly
as low as -4. This should be sufficient to turn the character of
the precipitation to more convective driven, so have gone with
showers with embedded thunderstorms. Noting showalters of -2 to
-4, cannot rule out some locally strong storms. With wetbulb
zero heights of 8000-9000 ft, small hail is a possibility.
There is also a very small chance of an isolated sever storm,
with the main threat hail of 1+" in diameter.
Precipitation should taper off from SW to NE this
afternoon/early this evening as the shortwave trough lifts to
Lows tonight should be near normal and highs Monday around 10
degrees below normal.
Long term /Monday night through Saturday/...
a closed low will slowly track from SW Ontario/north Great Lakes
Monday night to pres over southern Ontario will slowly track to
near the Quebec Ontario boarder by Thursday morning. There will
be shortwaves rotating around this rather broad closed low, that
could trigger some isolated to scattered showers from time to
time through Wednesday night, with the best chance over
The models then differ on how fast/far the closed low works to
the east Thursday-Saturday, in part because they differ on how
it is re-enforced from the west. As a result, the forecast from
Thursday on is of at best low-moderate confidence in the
For now it appears that Thursday and Thursday night should be
dry, with the region potentially in between main spokes of the
closed low. The next spoke then influences our weather Friday
or Saturday, so have just slight chance pops for now until the
timing of the system can be better refined.
Temperatures start out near normal Monday night and Tuesday,
should be above normal Wednesday, then near normal again
Aviation /18z Sunday through Friday/...
high pressure will remain fairly stationary to the east through
tonight. A frontal system will begin to approach late
tonight and cross the region on Tuesday.
Southeast winds of 8-12 kt this afternoon...with gusts 15 to 20
possible. Gusts diminish this evening...but then east/southeast winds
increase for coastal terminals to 10 to 15 kt late tonight into
Monday morning as a wave of low pressure tracks to the south.
Gusts to 20 kt possible.
Will have to watch along the coast for development of low clouds
in the onshore flow tonight. Meanwhile deteriorating conds late
tonight...with MVFR conds developing for the NYC Metro terminals
towards 06z, with IFR conditions possible by daybreak Mon in
developing rain. Potential for sparse tsra heading into morning
Outlook for 12z Monday through Thursday...
Monday...IFR conds likely. Rain likely and chance of tstms in
the morning into early aft. -Dz possible in aft. East gusts to 20
kt along the coast in the morning...lighter NE winds in the
Monday night...MVFR or lower conds possible
Tuesday...chance of showers and possibly a tstm with brief with
MVFR or lower conds in the afternoon/evening.
Wednesday...mainly VFR. Chance of showers/tstms mainly northwest of
the NYC Metro terminals.
the forecast appears to be on track.
In the near term, will be watching the ocean waters and eastern
Long Island Sound for development of any fog later today into
this evening. Given a second night moist onshore low level
flow, cannot rule out the possibility of fog later today into
An Small Craft Advisory may be needed for the ocean waters late tonight into the
daytime hours on Monday. Increasing southeast flow looks to peak at
20g25kt Monday morning, with Max seas per wavewatch and buoy
wind/wave climatology 5, maybe 6 ft, with the higher conditions
and longer duration more likely to be out east during the
daytime hours on Monday.
Otherwise, sub-advy conditions expected through Thu night.
total rainfall amounts tonight and Monday could range from
around 1/3 to 1/2 of an inch, with locally higher amounts
possible in areas experiencing strong convection Monday. In
areas that do experience strong convection, there is the
potential for at least localized ponding of water on roadways.
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 likely increase a bit with
strengthening 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, and along the
kill Van kull and Arthur kill around Staten Island and adjacent
portions of New Jersey.
Additional minor flooding may occur with the high tide cycle
Monday night in the areas that have been affected over the last
New York...coastal flood advisory from 10 PM this evening to 3 am EDT
Monday for nyz075-178-179.