Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service New York New York
732 am EDT Monday Apr 21 2014

Synopsis...
high pressure retreats to the east through tonight. A cold front
approaches from the west Tuesday morning...then crosses the tri-
state Tuesday afternoon and evening. High pressure then builds
into the region for the middle to the end of the work week. Low
pressure and a frontal system then impacts the region at the end
of the week and into the weekend.

&&

Near term /until 6 PM this evening/...
some patchy stratus developed over southeast CT and into the North Fork
of Long Island. That should dissipate over the next couple of
hours as temperatures continue to warm into the 40s.

Otherwise...will adjust hourly grids based on latest surface observation and
infrared Sat img.

Northern stream ridge over SW Ontario/upper Midwest builds over
the area today. Associated subsidence will keep things dry with
minimal cloud cover...other than a few passing high clouds from
time to time.

For highs today used a blend of mixing down from 950-925 hpa per
BUFKIT soundings...with NAM 2-meter temperatures and a blend of
mav/met guidance. Limited mixing due to subsidence...plus onshore
flow will keep temperatures cooler than 850 temperatures around
10c would usually imply...with middle-upper 50s at the immediate
coast...and generally low-middle 60s elsewhere. However...should see
some scattered readings in the upper 60s across portions of NE New Jersey
and the lower Hudson Valley.

&&

Short term /6 PM this evening through 6 PM Tuesday/...
ridge axis slides to the east tonight...allowing for high then middle
clouds to build in overnight from west to east. For lows used a blend of
mav and met guidance with values forecast a few degrees above
normal.

700-500 hpa longwave trough approaches Tuesday...along with
surface-850 hpa cold front. GFS appears to be progressive outlier
with how fast front and precipitation moves through...so used a
non-GFS blend for the forecast on Tuesday.

Tuesday morning should be dry through out...with mainly a scattered-broken
middle deck across the region.

Showers should begin to work into western zones early-middle
afternoon...then across the remainder of the area late in the
afternoon. Appears there could be enough instability over most of
NE New Jersey and mainly west portions of the lower Hudson Valley - NAM has a
few hundred j/kg of cape by late afternoon...and both NAM and GFS
BUFKIT soundings have total totals at kswf get to 51 - so have
slight chance of thunder in those areas in the afternoon as well.
Marine influence farther east should preclude any thunder from
forming farther east...and should promote the rapid weakening of
any stronger convection which were to move in from the west.

Noting wet bulb zero heights around 7000 feet...level of free
convection below 1000 M...and 500 hpa temperatures around -16 to
-18c would not be surprised at some small to possibly marginally
severe hail with the strongest convection.

For highs Tuesday used a blend of mav/met guidance...NAM 2-meter
temperatures and mixing down from 975-925 hpa per BUFKIT
soundings. Highs in coastal areas should be near to slightly above
normal...and inland should run around 5 degrees above
normal...with a few spots reaching or getting just above the 70
degree mark.

&&

Long term /Tuesday night through Sunday/...
some discrepancies with the models Tuesday night with the passage
of the frontal system. Cold front slides through the region in the
evening and will be clear of eastern zones by daybreak Wednesday.
GFS is the fastest of the models and has precipitation ending pretty much
from 00-06z...but the European model (ecmwf)/NAM/sref/CMC are a bit slower and ends
precipitation a but later. Either way...will carry the highest probability of precipitation
early...and will taper down to chance by midnight. With upper
trough and strong shortwave following behind the front...will keep
slight chance probability of precipitation in the forecast through Wednesday morning.

High pressure builds in behind the departing front. Skies clear out
during the day...and the pressure gradient tightens...resulting in a
strong northwest flow of 20-30 miles per hour with the potential for gusts up to 40
miles per hour.

Winds diminish Wednesday evening as the gradient relaxes as the high
builds east...and then will be nearly overhead on Thursday. Gusty
conditions could develop again across eastern zones during the day.

The high departs Thursday night as a frontal system approaches from
the west. That system will impact the region for the end of the week
and into the weekend. For now...will carry chance probability of precipitation from mainly
Friday afternoon through Saturday night.

Strong northwest flow will usher cold air advection into the region for Wednesday and
Thursday...and highs will be in the upper 50s to around 60 both
days. For the end of the week...temperatures warm back up into the low to
middle 60s. Lows will be in the 30s/40s Wednesday night and Thursday
night...and then in the 40s at night for the end of the week and
into the weekend.

&&

Aviation /11z Monday through Friday/...
high pressure over the area this morning weakens and gradually
shifts east through Tuesday as a cold front approaches from the
west.

A combination of shallow low-level moisture and radiational
cooling has allowed for the development of a small area of IFR
ceilings across southeast CT and Rhode Island. Kgon reporting a ceiling of 400 feet at 11z.
Daytime heating should dissipate this area fairly quickly.

Otherwise VFR through the taf period. Moderate confidence in
wind forecast. Sea breeze will be likely this after...timing could
be +/- 1-2 hours at coastal terminals.

Winds veer from the NE this morning at less than 10 knots...to S/southeast
by this after...with local seabreeze enhancement. The NE flow will
hold on across klga into middle afternoon as is typical in a weak
flow during the Spring.

There is also low confidence in the development of IFR stratus
tonight in the onshore flow. There is limited guidance pointing
to this scenario. Typically...the first night of weak onshore
flow does not support the development of low clouds/fog.

... Metropolitan enhanced aviation weather support...

Detailed information...including hourly taf wind component forecasts
can be found at: http://www.Erh.NOAA.Gov/zny/n90 (lower case)

Kewr fcster comments: no unscheduled amendments expected.

The afternoon kewr haze potential forecast is green...which
implies slant range visibility 7sm or greater outside of cloud.

Kjfk fcster comments: no unscheduled amendments expected.

Klga fcster comments: no unscheduled amendments expected.

Kteb fcster comments: no unscheduled amendments expected.

Khpn fcster comments: no unscheduled amendments expected.

Kisp fcster comments: patchy MVFR/IFR ceilings possible to 13z.

Outlook for 12z Tuesday through Friday...
Tuesday morning...VFR...patchy IFR/MVFR possible.
Tuesday after-Tuesday night...rain showers becoming likely...with MVFR or lower
possible. Northwest-north winds g20-25kt at night.
Wednesday-Thursday night...VFR. Northwest-north wind g20-25 knots.
Friday...MVFR or lower possible in after with a chance of showers.

&&

Marine...
a light pressure gradient will keep winds 10 knots or less over all
waters through Tuesday morning...and over the non-ocean waters
through Tuesday afternoon. Southerly flow should increase to 10-15
knots over the coastal ocean waters Tuesday afternoon...however this
should not be enough to bring seas to 5 feet.

Cold front moves across the waters Tuesday night...and then high
pressure builds east for the middle to the end of the week. The
pressure gradient tightens on the waters for Wednesday/Thursday.
Winds ramp up to Small Craft Advisory levels late Tuesday night/Wednesday...and there
is the potential for gales on eastern waters Wednesday night and
Thursday. Winds/seas subside to sub-Small Craft Advisory levels Thursday night...and
then sub-Small Craft Advisory conditions currently expected for the end of the
week and into the weekend.

&&

Hydrology...
the potential for significant precipitation - widespread 1/2 inch
or more - is low through the week.

Note...minor flooding continues along the Connecticut River. For
additional information...please refer to the latest flood warnings
from National Weather Service Taunton Massachusetts.

&&

Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...none.

&&

$$

Synopsis...maloit/mps
near term...maloit/mps
short term...maloit
long term...mps
aviation...dw
marine...maloit/mps
hydrology...maloit/mps