Scientific Forecaster Discussion
fxus61 kokx 010426
Area forecast discussion
National Weather Service New York New York
1226 am EDT Mon may 1 2017
high pressure retreats off the New England coast tonight,
giving way to an approaching warm front over the mid Atlantic
states. The warm front passes to the north Monday morning. A
cold front then slowly crosses the tri-state Monday night into
Tuesday morning. Deepening low pressure over northern New
England will produce windy conditions on Tuesday. High pressure
builds in from the west on Wednesday, then low pressure will
bring rain for the end of the week.
Near term /until 6 am this morning/...
only change this update was to remove showers from forecast -
latest radar trends indicate should remain over far reaches of
upstate New York into far north New England. The remainder of the forecast
appears on track.
A highly amplified upper flow features a ridge moving off the
East Coast and a vigorous upper low lifting NE across the
A combination of low-level warm advection and an east-southeast flow will
allow for low clouds, fog, drizzle. The fog and drizzle are
more likely after midnight with potential for dense fog towards
Overnight lows will be near or slightly above normal in the mid
40s to lower 50s.
Short term /6 am this morning through 6 PM Tuesday/...
a vigorous upper low will track up through the Great Lakes
Monday night, sending a frontal system across the area.
There is some uncertainty with the timing of the warm frontal
passage in the morning. Preference is toward the slightly slower
high res models which are late in the morning/early afternoon
from S to north. Any fog/drizzle will lift out with some clearing
behind the warm front. Highs are forecast to get into the 60s at
the coast and the mid 70s inland. There is some uncertainty
with the influence of the marine layer at the coast, which may
take longer to scour out. This could keep temperatures cooler
than forecast along with slower dissipation of the fog/stratus.
Instability across the interior in the afternoon could result
in a few showers or an isolated thunderstorm, mainly north and
west of NYC. In addition...wind gusts into the 30s possible
across the interior with deeper mixing if breaks of sun develop.
Cold front and pre-frontal trough will likely produce a band of
showers and scattered thunderstorms overnight Monday. Loss of
daytime heating will likely limit these storm from becoming
severe. The environment is strongly sheared, but with Low Cape.
Rainfall amounts are forecast to be around a quarter inch with
localized higher amounts in any stronger convection.
Long term /Tuesday night through Sunday/...
the models were in good agreement through the extended, so the
superblend was generally used. Lapse rates steepen on Tuesday as
cooler temperatures aloft move in. The best chance for a stray
shower will be on the northern fringe of the forecast area with the
low level downslope flow a limiting factor. Deep mixing on southwest
flow all the way up through jet level will produce windy conditions.
This is a situation where the models may slightly underperform,
bringing winds close to advisory criteria from northeastern New
Jersey into New York City and surrounding areas. A dry day is
progged at this time for Wednesday based on the model consensus.
Temperatures will hit convective, but the subsidence will attempt to
offset the tendency for convective rainfall. Chances for overrunning
light rain then increase Wednesday night ahead of developing low
pressure over the Ohio Valley. The low then tracks through the area
Friday, bringing moderate rain to the tri-state region. Scattered
showers are possible over the weekend with cyclonic flow aloft
and increasing lapse rates.
Temperatures will be uniformly mild on Tuesday due to the deep
mixing. It is possible that highs end up a few degrees above the
model consensus. Readings will then cool on Wednesday with a colder
airmass in place. Cooler on Thursday and Friday due to the clouds
and rain, although nighttime temperatures will likely be above
normal due to these same elements. Temperatures close to or slightly
below normal are expected Saturday and Sunday due to deep
Aviation /06z Monday through Friday/...
high pressure drift offshore overnight. A warm front will
approach from the southwest late tonight and move through Monday
morning into afternoon.
IFR/LIFR conditions expected to develop from SW to NE in fog
and drizzle overnight. IFR/LIFR could be stubborn to improve
through the morning into early afternoon...particularly across
the northern and eastern terminals. A period of VFR conditions
possible for NYC/New Jersey Metro terminals in the late afternoon/early
East/NE winds tonight...eventually veering to the south with warm
frontal passage in the late morning/aft. Timing of the frontal
passage is tricky, likely to move through the NYC/New Jersey Metro
terminals before the northern and eastern terminals. South-southwest wind
gusts to 30-35 kt possible for kewr/kteb/kswf Mon afternoon if
breaks of sun develop. S winds 20 to 25 kt with gusts to 30 kt
possible for klga/kjfk/kisp with late aft/eve sea breeze.
Outlook for 00z Tuesday through Friday...
Monday night...conditions lowering back to MVFR/IFR for western
terminals...and likely LIFR for coastal terminals as showers
develop with a chance of thunderstorms. S winds 15 to 25 kt
likely for coastal terminals. Low level wind shear possible for kjfk/kisp/kgon
with SW winds 25-55kt at 2 kft.
Tuesday...showers ending Tuesday morning, becoming VFR. West-southwest
winds 20 to 30 kt with gusts 35 to 40 kt possible in the
Tuesday night-Wednesday night...VFR.
Thursday-Friday...MVFR or lower conditions with rain.
made minor changes this update to reflect the latest trends in
observations and guidance. The forecast appears on track.
Small Craft Advisory up for ocean waters through Tuesday, and nearshore waters
Monday afternoon through Tuesday. Primary hazard overnight into
Monday morning will be dense fog development...with vsby less
than 1 nm at times. The fog may be tough to scour out across
ocean waters and eastern sound and bays during the day.
Marginal E/se sca gusts and 4 to 6 ft seas on the ocean should
subside a bit towards daybreak...but then the pressure gradient
increases Monday afternoon with gusts up to 25 knots. A persistent
onshore flow will build seas to 5-6 ft over southern portions
of the coastal ocean zones on Monday as well.
The winds increase on Monday night, with solid small craft
conditions on all waters.
Small Craft Advisory conditions can be expected on Tuesday. There is
a chance for gale force wind gusts, particularly nearshore. Small
Craft Advisory level winds and seas can then be expected on the
ocean Wednesday, with marginal winds elsewhere. Winds and seas are
progged to remain below Small Craft Advisory levels on Thursday,
then low pressure will produce at least Small Craft Advisory
conditions on Friday and Saturday.
no hydrologic impacts are expected through Wednesday.
1-2 inches of rain is possible late Thursday through Friday
Marine...dense fog advisory until noon EDT today for anz330-335-338-340-
Small Craft Advisory from 2 PM this afternoon to 6 PM EDT
Tuesday for anz330-335-338-340-345.
Small Craft Advisory until 6 PM EDT Tuesday for anz350-353-355.