Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
352 am EDT Tuesday Oct 21 2014
low pressure develops over the Delaware-Maryland-Virginia area today...and then will
meander south of Long Island through the middle-week period. That low
tracks northeastward into the Canadian maritime provinces late
this week and into the weekend. A cold front approaches
Saturday...then crosses the area Saturday night. High pressure
builds into the Middle Atlantic States early next week.
Near term /until 6 PM this evening/...
deep upper trough with several strong shortwaves deepens over the
eastern Great Lakes area. Meanwhile...surface low pressure develops over
the Delaware-Maryland-Virginia area and slowly tracks towards the western Atlantic
waters just south of Long Island late in the day.
Can expect scattered showers throughout the day today...but not
much precipitation is expected. A few isolated thunderstorms possible late this
afternoon due to steepening low level lapse rates...but would
expect a rumble of thunder or 2. Highest probability of precipitation will be over western
zones and areas closer to the base of the trough.
Highs today will be mild...topping off in the middle to upper 60s.
Temperatures could be a bit warmer if parts of the County Warning Area become dry slotted
and skies break up and the sub probability of precipitation out for a brief time.
Short term /6 PM this evening through 6 PM Wednesday/...
scattered showers continue tonight...but rain becomes likely over
western zones as the low deepens. Rain then continues through the
day Wednesday as the upper low moves towards the Delaware-Maryland-Virginia...and
becomes a nearly vertically stacked low with the aforementioned
surface low. Will bump up probability of precipitation to likely/categorical on Wednesday as
that low meanders south of Long Island.
Much cooler on Wednesday with highs only in the low to middle 50s.
Long term /Wednesday night through Monday/...
stacked low pressure just south of Long Island will slowly drift
north/northeastward late this week. Shortwave energy out of
central Canada dives southeast and moves across northern New
England this weekend. Some differences are noted with the strength
of this shortwave. Upstream Pacific northwest shortwave will kick out
eastern trough...resulting in ridging between the two troughs
early next week.
At the surface...some model placement differences noted with
regard to the surface low pressure. Generally expect surface low just
south of Long Island Wednesday night to slowly move northeastward
between eastern Long Island and the 40n/70w benchmark Thursday.
The low will track to the northeast late in the week toward the
Canadian maritime provinces this weekend. A cold front looks to
move through late Saturday or Saturday night...followed by high
pressure early next week.
As for sensible weather...will maintain moderate rain Wednesday
night...with low categorical probability of precipitation or likely probability of precipitation into Thursday as
the stacked low is slow to move out. Banded precipitation
likely...providing additional measurable quantitative precipitation forecast most locations.
Some surface based instability is noted closer to the middle/upper level
low...or eastern portion of the County Warning Area Wednesday night and Thursday per
NAM/GFS. Weak middle level instability is prognosticated by these models as
well. Cannot rule thunder...but this should be too isolated to
Dry weather eventually returns Friday through Monday as the storm
Daytime temperatures should remain cooler than normal Thursday due to
clouds and periods of rain. Thereafter...temperatures likely rebound
closer to...if not slightly above normal. Sunday could be the
coolest day behind the frontal passage...while temperatures have the
potential to warm above seasonal norms early next week in SW flow.
Aviation /08z Tuesday through Saturday/...
low pressure approaches from the northwest through tonight...then
becomes nearly stationary across New York...Pennsylvania...and into
Virginia Tuesday as another low develops off the coast.
Tricky forecast next 24 hours with a weak pressure gradient for most
of the period leading to light and vrb winds. Tried to pinpoint a
direction...but directions could be all over the place until the
low tracks to the S of the area and a NE flow between 5 and 10 knots
develops this evening.
Conds should be VFR for the majority of the period...but could see
isolated MVFR in any rain that moves directly over any of the
terminals. Speaking of rain...tough to pinpoint when and where but
do not expect a prolonged period of precipitation at any of the
terminals...except kswf. Am probably too early in steady -radz
beginning at 23z tonight...but further adjustments can be made in
Outlook for 06z Wednesday through Saturday...
Tuesday night...MVFR to locally IFR conds developing with scattered light
Wednesday through Thursday...MVFR or lower conds in rain. Northerly flow 10 to 15
Friday...improving conds. Northwest winds 15-20 knots with 20-25 knots gusts.
Sat..VFR. Northwest g20kt.
persistent southerly flow pushed seas up to 5-6 feet on the ocean
waters. Will issue Small Craft Advisory for hazardous seas this morning. Winds
lighten and shift to the southeast late this morning...and seas should
subside to 3-4 feet then.
Otherwise...mainly tranquil conds on the waters as low pressure
develops south of the waters. Gradient tightens on Wednesday...and
Small Craft Advisory conds likely by afternoon. Will hold off on issuing Small Craft Advisory due to
Small Craft Advisory that is up for this morning.
Gusty north winds Wednesday night will turn toward the north/northwest Thursday as
the area of low pressure just south of Long Island makes slow
progress northeastward. Gusty northwest winds persist Friday and
Saturday. The winds may briefly back to the west late Sat ahead of
the cold front.
Rough sea conditions are expected to slowly improve late in the
week and into Saturday. Westerly fetch though likely results in
higher seas further east.
scattered showers...and possibly a thunderstorm...will result in a
tenth of an inch of quantitative precipitation forecast or so through tonight. Rain increases late
tonight through Wednesday...with 1/2 to 3/4 inch quantitative precipitation forecast likely.
Localized nuisance urban or poor drainage flooding is possible.
Periods of rain...briefly heavy is spots...could result in
localized nuisance urban or poor drainage flooding Wednesday night and
Storm totals should average between 1 and 2 inches per analysis of
operational models...and sref members. This amount of rain should
not result in any serious life threatening or property flooding
Marine...Small Craft Advisory for hazardous seas until 11 am EDT this
morning for anz350-353-355.
long term...precipitable water