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Area forecast discussion 
National Weather Service Mount Holly New Jersey
945 am EST Wednesday Jan 28 2015

Synopsis...
deep low pressure across the Canadian maritime provinces will
continue to weaken today. High pressure will build across the area
this afternoon through Thursday before moving east. Low pressure
will move across the Great Lakes and New England Thursday night
through Friday and cause an Arctic front to cross our region. More
high pressure will return for much of the weekend. A storm will
approach the area Sunday afternoon and affect the area into early
next week.

&&

Near term /until 6 PM this evening/...
high pressure is presently centered over the Ohio Valley with low
pressure located over the Canadian Maritimes. The pressure
gradient between these two systems is producing a sustained
northwest of 10-20 miles per hour with slightly higher gusts over the middle
Atlantic. The gusty winds combined with fairly cold temperatures
today will make it feel even colder outside.

The pressure gradient and resultant wind field will gradually
relax throughout the day across our region as the coastal low
weakens to our northeast and high pressure builds in from the
west. Full sunshine and adiabatic warming associated with the
strengthening subsidence inversion and downsloping winds off the
higher terrain should all help moderate the airmass a bit.

Nonetheless, we are in store for another colder than normal day.
For the maximum temperature forecast, trended toward the warmer mav guidance
and even above guidance in some places after factoring a 2-3f
degree model cold bias yesterday.

&&

Short term /6 PM this evening through 6 am Thursday/...
height rises will occur along the eastern Seaboard tonight as an
upper ridge progresses eastward. At the surface, high pressure over
the Appalachians this evening will build directly overhead during
the overnight.

Min temperatures will depend on how quickly the boundary layer can
decouple. Once decoupling happens, airmass will radiate quite
effectively under light winds and clear skies. The official min temperature
forecast is on the cold envelope of model guidance given the
favorable radiational cooling setup and with a fresh snowpack. Min
temperatures are in the single digits north and east of I-95 and low to middle
teens in the cities and along the coast/Delaware-Maryland-Virginia where the pressure
gradient will take the longest to weaken.

&&

Long term /Thursday through Tuesday/...
Thursday through Friday...a fast moving low pressure area over the western
Great Lakes Thursday morning will pass just north of the area Thursday night
and then deepen off the New England coast Friday. An Arctic cold
front will cross the area Friday. This system will produce a
widespread snow across mostly the northern half of the forecast area.
Probability of precipitation were raised a bit with both the ec and GFS models in general
agreement. The GFS 00z is slightly faster with the system.
Temperatures in the (mostly likely) precipitation areas support snow
with amts probably in the 1 inch range in most areas. A couple 2
inch amts possible far north over northern New Jersey or the southern Poconos. We have
gone along with the totals which are supported by the latest westward.
Winds and becoming very cold later Friday with wind chills dropping
into the single digits north and teens over phl and Delaware-Maryland-Virginia by
evening.

Friday night through Sunday...high pressure builds in and remains for
the weekend. Bitter cold Sat with temperatures some 15 to 20 degrees below
normal. Some moderation in temperatures sun...but still mostly 5 to 10
degrees below normal. Flags for wind chill possible Friday night and
Sat across the far north.

Sun afternoon through Monday night...more weather action as the next
system emerges from The Rockies Sat night then tracks up the Ohio
Valley and across our area Sun night/Monday. The system is shown
scooping up plenty of moisture before it arrives. The GFS shows a
track just north of the area...the ec just south. Temperatures and probability of precipitation
mostly wpc like with a few adjustments for better isc coordination.
Chance snow Sun afternoon...then likely snow Sun night. Snow changes to
rain S/east I-95 Monday. There will be plenty of refinements...so this
is the best forecast for now. Pay attention to this system over the next
few days.

Tuesday...another dry high pressure system with another plunge of
Arctic air for Tuesday and probably into Wednesday. Temperatures possibly 10 to 20
degrees below normal.

&&

Aviation /15z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

VFR today and tonight. Northwest winds 10-15 knots will gust up to 25 knots this
morning and 20 knots this afternoon. Light winds tonight.

Outlook...
Thursday...mostly VFR. Lower conditions with snow possible west late.

Thursday night through Friday...lower conditions with precipitation Thursday night. Lingering
showers early Friday with gusty winds.

Friday night through sun...mostly VFR. Small chance for snow Sun afternoon.

&&

Marine...
Small Craft Advisory remains in effect for the area waters today. Only change was
to extend the ending time of the Small Craft Advisory for the Delaware Bay to 6 PM
(matching the ending time of the coastal waters) as the northwest
direction will channel down the Bay, enhancing wind speeds to near
25 knots. Wavewatch guidance verified 1-2 feet too low with wave
heights in the coastal zones, so increased seas a bit to 5-8 feet
for this morning.

Northwest winds and seas will subside tonight. No marine hazards are
expected other than light freezing spray.

Outlook...
Thursday...sub Small Craft Advisory conditions.
Thursday night...building winds/seas Small Craft Advisory conditions.
Friday/Friday night...gale conditions possible.
Sat...gale conditions diminishing back to Small Craft Advisory conditions.

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...Small Craft Advisory until 6 PM EST this evening for anz430-
431-450>455.

&&

$$
Synopsis...O'Hara
near term...Klein/meola
short term...Klein
long term...O'Hara
aviation...Klein/O'Hara
marine...Klein/O'Hara

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