Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 230936
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
536 AM EDT Thu Mar 23 2017

.SYNOPSIS...
High pressure will build across the east coast today, then
shift offshore tonight. A warm front will lift to our northwest
Friday, then a backdoor cold front pushes through the area
Saturday. This front is forecast to stall near the southern
portions of the area through Sunday, but may return northward as
a warm front Sunday night into Monday. A couple of low pressure
systems are forecast move across the east coast through early
next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Sprawling 1036 MB high centered over the eastern Great Lakes
will slowly build to the south and east today. By late
afternoon, the center of the high will be just off the Eastern
Seaboard.

This high will continue to bring a continental Polar airmass
into the region with high temperatures 10-15 degrees below
normal. Highs will top off in the 30s in the Poconos, and in the
low to mid 40s for the rest of the CWA.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
High pressure off the Eastern Seaboard will continue to drift
offshore tonight, and a warm front lifts towards the Mid-
Atlantic and Northeast late in the overnight.

The main question will be how cold temperatures drop this
evening, as skies will be clear, and with the center of the high
near the region, winds will be light. This results in strong
radiational cooling conditions prior to midnight.

Temperatures should drop into the low-mid 20s for most of
NJ/PA, especially for the Poconos, Lehigh Valley, northern NJ,
and the Pine Barrens of NJ. It is possible that temperatures
could be even colder.

After midnight tonight, clouds will build into the region, and
temperatures will then hold steady and slowly rise.

Think precip will hold off until after the end of the tonight
period, so will keep precip out of the forecast. If precip does
develop, it will start out as a wintry mix of sleet/freezing
rain, mainly over the Lehigh Valley/Poconos.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
A warm front will lift to our northwest during the morning
hours on Friday, while a couple of short wave/vorticity impulses
slide across the area as well. This is expected to help create
an area of precipitation that is forecast to move across the
area during the morning into the very early afternoon hours.
Timing of the precipitation will be critical, because depending
on how early this precipitation begins, there could be a period
of a wintry mix of freezing rain/sleet/snow across portions of
eastern Pennsylvania and northern New Jersey. With the
uncertainty of the timing, and the fact it is expected in the
3rd period, we will hold off on an advisory at this time. The
rest of the area should remain all rain with warmer
temperatures.

Friday night is expected to remain dry as the precipitation
associated with the warm front moves away from the area. A
backdoor frontal boundary is forecast to approach the area from
the north overnight, but will likely not reach the area until
the daytime Saturday.

Saturday begins an extended period of possible unsettled
weather across the area. A backdoor cold front will sink through
the area during the day Saturday, then likely stall just to our
south through Sunday. There will be a chance of showers across
the area Saturday through Sunday, but areas across the northern
half of the area have the best chance.

The frontal boundary is then forecast to lift back northward as
a warm front overnight Sunday into Monday as an area of low
pressure may develop along the boundary and move across the
area. Another couple of short wave/vorticity impulses are
forecast to move across the area as well, and will enhance
precipitation potential across the area. Sunday night into early
Monday morning has the greatest chance of seeing more
widespread and heaviest precipitation potential.

Unsettled weather continues into early next week as a couple of
low pressures affect the east coast, which may eventually bring
a cold frontal passage across the east coast by mid week. There
will continue to be a chance of showers through Wednesday as
several short waves/vorticity impulses slide across the area,
before the possible frontal passage Tuesday night.

&&

.AVIATION /10Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

VFR through 06Z Friday with unlimited CIGs/VSBYs.

NW winds 5-10 KT, backing to the W after 18Z. Winds become
LGT/VRB after 00Z Friday.

High clouds will move in from the west after 09Z Friday. Precip
should hold off until after 12Z Friday, but it is possible for
some sleet/freezing rain at KABE/KRDG between 10Z-12Z Friday.

OUTLOOK...

Friday...A period of MVFR or slightly lower conditions possible
with a period of light rain; mostly during the morning into
early afternoon. If precipitation begins early enough, a wintry
mix is possible, especially for northern areas. Southwest winds
may gust 20- 25 knots.

Friday night...Conditions improving to VFR.

Saturday-Monday...MVFR or IFR conditions with periods of rain
possible.

&&

.MARINE...
Small Craft Advisory conditions on the ocean waters will
gradually subside early this morning. Tranquil conditions then
in place for the rest of the day and tonight as high pressure
builds in from the west.

OUTLOOK...

Friday-Friday night...Small Craft Advisory conditions likely to
return to the waters.

Saturday-Saturday night...Conditions expected to fall below
advisory levels.

Sunday-Monday...A return to Small Craft Advisory levels
expected. Winds may fall below advisory level Sunday night into
Monday, but seas are expected to remain above advisory levels.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 8 AM EDT this morning for
     ANZ450>455.

&&

$$
Synopsis...Robertson
Near Term...MPS
Short Term...MPS
Long Term...Robertson
Aviation...Drag/Robertson/MPS
Marine...Robertson/MPS


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