Scientific Forecaster Discussion
fxus61 kokx 302231
Area forecast discussion
National Weather Service New York New York
631 PM EDT sun Apr 30 2017
high pressure retreats off the New England coast this evening,
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 Monday morning/...
cloud cover was increased based on satellite, otherwise the
forecast was on track this evening. A highly amplified upper
flow features a ridge moving off the East Coast and a vigorous
upper low lifting NE across the Mississippi Valley. The latter
of which will track up through the Great Lakes Monday night,
sending a frontal system across the area.
High pressure retreats off the New England coast this evening,
with a warm front over the mid Atlantic states working
northward. A combination of low-level warm advection and an east-southeast
flow will allow for low clouds, fog, drizzle to develop
overnight. This may even be preceded by a period of light rain
this evening. The fog and drizzle are more likely after
midnight with visibilities a mile or less.
Overnight lows will be near or slightly above normal in the mid
40s to lower 50s.
Short term /6 am Monday morning through Monday night/...
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. 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.
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 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 /00z Monday through Friday/...
high pressure remains centered off the New England coast,
extending into New Jersey. The high begins to drift offshore
late this afternoon and tonight. A warm front will approach
from the southwest late tonight and move through sometime
VFR, with clouds lowering through this afternoon, becoming MVFR
23z or soon after. IFR conditions are likely by late evening,
03z to 04z, with fog and drizzle developing. IFR conditions
will develop later at kswf and kgon, after 07z. Conditions
improve Monday morning into the afternoon, with MVFR ceilings.
Gusty east to southeast wind are the main issue this afternoon
and evening. Winds become more southeasterly, and gusty, as the
high built into the terminals. Winds are now expected to remain
from the southeast until late tonight, then possibly briefly
become east to northeast and light, or light and variable as
the warm front approaches. With the warm front passage Monday
morning, winds shift to the south. Timing of the frontal passage
is uncertain at this time, and will likely move through the
inland terminals before the coastal terminals, and farther
Outlook for 18z Monday through Friday...
Monday afternoon ... there is a possibility that ceilings
become VFR briefly.
Monday night...conditions lowering back to IFR to LIFR as showers
develop with a chance of thunderstorms. Low level wind shear possible.
Tuesday-Wednesday night...showers ending Tuesday morning, becoming
Thursday-Friday...MVFR or lower conditions with rain.
Small Craft Advisory up for all waters Monday into Tuesday.
A moderate pressure gradient over the waters tonight will
result in east-southeast winds of 15 to 20 knots. 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...Small Craft Advisory from 6 PM Monday to 6 PM EDT Tuesday for
Small Craft Advisory from 6 am Monday to 6 PM EDT Tuesday for