Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service New York New York
1118 PM EDT Tue Apr 25 2017
weakening low pressure will move slowly up the mid Atlantic
coast through Wednesday, pass southeast of Long Island Wednesday
evening, and then dissipate east of New England later Wednesday
night. A weakening cold front will approach from the northwest
Thursday and Thursday night, then also dissipate over the area
on Friday. Another cold front will approach from the north
Friday night and Saturday, then presses to the south Saturday
night. The front will then gradually lift north as a warm front,
pushing to the north of the area Monday. A cold front will then
move across Monday night, followed by weak high pressure
building in on Tuesday.
Near term /until 6 am Wednesday morning/...
minor adjustments were made based on the latest observations and
near term forecast trends.
Most storm total rainfall amounts ranged from 1/2 to 1 inch with
isolated higher amounts. Brief heavy downpours caused minor
flooding of low lying poor drainage areas.
Northeast wind gusts of 30 to 40 mph are now decreasing.
Widespread minor tidal flooding occurred with the evening high
tides across the south shores of New York Harbor and the back bays of
long Island's Atlantic South Shore bays.
Otherwise, the main area of hvy rain with embedded tstms has
shifted further east along with the nose of the low lvl jet. The
main focus for heavier rain will shift east, mainly across Long
Island and southern CT overnight.
Low temps tonight will be in the lower 50s.
Short term /6 am Wednesday morning through Wednesday night/...
on Wednesday, the stacked low will be slowly moving south and
east of Long Island. Expect scattered showers to continue,
mainly in the morning and especially over Long Island and
southern CT, then tapering off in the afternoon.
The close proximity of the stacked low should keep low clouds
around through the day and possibly some patchy fog, with highs
mainly in the lower 60s.
As the upper low passes just to the southeast Wed night, could see some
redevelopment of showers mainly across Long Island mainly after
midnight. Lows will again be in the 50s.
Long term /Thursday through Tuesday/...
northern stream ridging builds over the area on Thursday keeping
things dry. However, underneath the associated subsidence inversion,
the lowest 100-150 hpa will be fairly saturated, so have increased
cloud cover and decreased temperatures on Thursday. For now
generally going 60-70 across the region, though there is some
potential these could be 5 to maybe even 10 degrees to warm.
A northern stream shortwave passes to the north Thursday night
warranting chance pops over northwest 1/3 of the County Warning Area and slight chance pops
elsewhere. With showalters progged to fall to 0 to2, have added
thunder to the forecast as well. Lows Thursday night should be
around 10 degrees above normal.
A northern northern stream shortwave passes by, a little closer
this time, on Friday, warranting chance pops everywhere. Showalter
indices warrant a chance of thunder.
Note, the GFS is faster than most other solutions with the
associated cold front, so used a non-GFS blend for timing the cold
front and precipitation. As a result, could see locations away from
the coast have highs from the mid 70s to around 80. As a result,
areas mainly west of the Hudson could see convective available potential energy in the afternoon of
around 1000 j/kg along with 40-50 kt of shear so some strong to
severe storms are possible there Friday afternoon.
The region is under quasi zonal flow Friday night-Saturday as
ridging builds to our south and a northern stream trough passes to
the north. Friday night should be dry, but could see some isolated-
scattered showers and possibly a thunderstorm by Saturday
afternoon/evening ahead of a backdoor cold front. Favored the faster
European model (ecmwf) timing of the front (based on historical Superior European model (ecmwf)
handling of backdoor fronts vs. The gfs).
Deep layered ridging builds over the area Saturday night-Sunday
night, then the axis slides to the east on Monday. At the surface,
the back door front pushes well to the south by Sunday morning, then
slowly lifts to the north as a warm front, lifting to the north on
Monday. The surface warm front motion warrants a slight chance of
rain Sunday and a chance of rain Sunday night. There is then a
chance of showers Monday morning and a chance of showers and
thunderstorms Monday, once solidly in the warm sector.
A vigorous northern stream trough approaches Monday night, then
lifts to the north on Tuesday, with its associated surface cold
front pushing through Monday night. As a result, have a chance of
thunderstorms Monday night, then a slight chance of showers Tuesday.
Temperatures Friday-Tuesday were based on the superblend, with NAM 2-
meter temperatures and a mix down from 975-925 hpa per BUFKIT
soundings added in on Friday. Temperatures should remain well above
normal during this time frame, with Saturday the warmest day - with
highs around 80 in the NYC Metro.
Aviation /03z Wednesday through Sunday/...
low pressure slowly moves up along the mid-Atlantic coastline
tonight and over the region Wed afternoon into Wed night.
Heaviest rain will continue to move east of the NYC/New Jersey Metro
terminals...and is expected to slide through eastern terminals
through the overnight. Brief IFR conditions expected in heavy
rain showers. Generally expect IFR/LIFR cigs tonight...with vsby
gradually coming down to IFR overnight into early Wed morning.
IFR cigs expected to linger through the day Wednesday...with
gradual improvement to MVFR/VFR vsby.
East/northeast winds prevail. Strongest winds are shifting east
of NYC/New Jersey Metro terminals...with speeds of 15 to 20 kt and
gusts 25 to 30 kt for the eastern terminals. Winds subside and
back more to the NE after midnight late tonight. Low level wind shear possible
this evening with southeast winds 45-50 kt at 2kft, for eastern
terminals overnight. Generally NE winds less than 10 kt on Wed.
Outlook for 00z Thursday through Saturday...
Wednesday night...potential for LIFR/vlifr in fog.
Thursday...IFR/LIFR potential to start...with gradual
improvement to VFR.
Friday...chance of MVFR in showers/thunderstorms.
Small Craft Advisory conditions occurring on all waters as expected. Winds on the
western ocean waters, western Long Island Sound, and possibly New York
Harbor could briefly peak at 35 kt this evening before
Winds should diminish overnight, with advy conditions abating on
The Harbor/sound/bays by 06z. Lingering ocean swells above 5 ft
and also 1 ft above wavewatch and nwps are likely to continue
into at least Wed night.
A relatively relaxed pressure gradient Thursday-Sunday will keep
winds over the waters around Long Island to 15 kt or less.
However, gradually diminishing swells will keep seas over all or
parts of the coastal ocean waters at or above 5 ft through
Friday night. All waters should experience sub-advy conditions
Saturday and Sunday.
total rainfall of 0.75 to 1.5 inches is expected through
Wednesday. The highest amounts are most likely to occur across
northeast New Jersey, also across southern CT. Hourly rainfall
rates close to 1/2 inch per hour with the heaviest rain could
cause brief/localized poor drainage flooding.
No significant (0.5 inches or more) widespread rainfall is forecast
from Thursday through at least Monday. However, isolated strong
convection could produce locally heavy rainfall Friday and again on
Monday. In areas where this occurs, there is the potential for the
ponding of water on roadways and a very low chance of minor flooding
of known poor drainage areas.
widespread minor coastal flooding occurred across the lower
New York/New Jersey Harbor, the South Shore bays of western Long Island
including Queens and Brooklyn this evening; with locations
along the western Long Island Sound expected to experience the
same through the midnight high tides.
Minor coastal flooding thresholds may be briefly and locally be
exceeded along the southern bays of western Long Island with the
Wednesday morning high tide. Right now at most it would appear
that a statement could be needed for southern Nassau.
Minor coastal flooding is possible with Wednesday night's high
tide cycle. Best chances for minor inundation will be at the
South Shore back bays of Nassau and Queens, but a statement
could be needed for other areas as minor thresholds have a
chance to just be reached in a few spots. Only 1/3 to 3/4 of a
foot of surge is needed to reach minor flood thresholds Wed
In addition, the elevated water levels combined with a
prolonged period of 5-9 ft breaking surf tonight into Thu will
result in beach erosion issues and may cause some localized dune
toe erosion during the high tides tonight into Wed night.
CT...coastal flood advisory until 1 am EDT Wednesday for ctz009-010.
New York...coastal flood advisory until 1 am EDT Wednesday for nyz071-073-
Coastal flood advisory until 11 PM EDT this evening for nyz080-
Marine...Small Craft Advisory until 2 am EDT Wednesday for anz330-335-
Small Craft Advisory until 6 am EDT Thursday for anz350-353-