Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 231154
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
654 AM EST Fri Feb 23 2018

.SYNOPSIS...
High pressure builds offshore of New England today as an area
of low pressure moves out of the Great Lakes region and across
southeast Canada tonight. A warm front to our south is forecast
to lift across the area tonight, followed by a cold front early
Saturday morning. The cold front will likely get hung up across
our southern areas Saturday, or just to our south, before
lifting back northward slightly Saturday night into Sunday as an
occluded frontal boundary moves across the area during the day
Sunday. High pressure begins to build into the region Monday
night and Tuesday, before moving offshore Tuesday night. A
backdoor cold front may approach the area from the north
Wednesday, before a warm front and occluding low pressure system
is forecast to approach the area from the south Thursday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Forecast was updated with higher PoPs to reflect band of showers
moving east along the Mason-Dixon line and into south Jersey.
Another area of rain is back over Ohio and may reach areas north
of PHL this afternoon. Some light precip could still affect the
Poconos this morning.

Previous discussion...
The surface analysis early this morning shows high pressure
centered over ME with a ridge axis extending southwest across
the mid- Atlantic region. This high has pushed the cold front
southward into NC. A cool northeast flow around the high
continues but with cloud cover temps overnight have dropped only
a few degrees. Just above the cool layer at around 5K ft the
winds reverse direction resulting in warm advection and
development of some showers across northern MD and southeast PA.
This precip is expected to spread or develop northeast across
the forecast area today.

We will keep the winter weather advisory going for Carbon,
Monroe and Sussex counties in our far north, as morning temps
seem to be below freezing at higher elevations and MPO is
reporting freezing fog. It is not clear how much precip and ice
accumulation can occur this morning before temps rise above
freezing, but there is enough of a threat to keep the advisory
in place for now. Rain should become fairly widespread across
the region this afternoon, but with higher PoPs generally north
of PHL. Later today the high pressure is forecast to weaken and
move offshore, with winds veering more to the southeast as the
front begins to return north as a warm front. Afternoon high
temps should be mostly in the 40s but may reach low 50s in
southern DE.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
For tonight, rain should taper off by early evening but some
drizzle and fog may persist overnight. Winds will become light
SW and temps will hold steady or even climb a few degrees,
especially south of PHL. A weak cold front is forecast to
approach from the NW overnight, but this should have no effect
other than a possible wind shift towards morning.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
An unsettled weekend is expected coming up, then dry weather
returns again for the early to middle of next week, then more
rainfall possible later in the week.

By Saturday morning, a frontal boundary is expected to be
moving into the area from the west and slowly move across the
area during the day. The front is eventually expected to become
nearly stationary across our southern areas, or just to our
south later on Saturday into Saturday night. Several short
wave/vorticity impulses are forecast to move across the area
Saturday into Saturday night, which will lead to enhanced lift
across the area and a couple of rounds of precipitation.

Then on Sunday, the front to our south will begin lifting
northward, but likely not make it very far across the area as an
occluded frontal boundary and possible triple point low move
across the area. As a stronger short wave/vorticity impulses
moves across the area, there will be enhanced lift and moisture
moving across the area, especially across potions of eastern
Pennsylvania and northern New Jersey. This will lead to a period
of potentially moderate to heavy rainfall Sunday morning. The
rainfall will taper off through the day Sunday once the occluded
front passes to our east, then conditions dry out Sunday night.

Precipitation amounts across portions of eastern Pennsylvania
and northern New Jersey could top 1-2 inches over the weekend,
with areas farther south 0.5-1 inch. Local rivers and creeks
will see some rises through the weekend into early next week,
and there could be the potential for poor drainage and low lying
flooding Sunday with the heavier rainfall.

After this period of rainfall over the weekend, dry weather is
forecast to return to the area for early next week. High
pressure is forecast to begin approaching the area from the west
on Monday, then fully build across the east coast Tuesday,
before moving offshore Tuesday night. This will bring dry
conditions Monday through Tuesday, expect possibly some light
rain across the southern areas Monday if the front to the south
remains close enough to push some moisture across the area.

On Wednesday, a back door cold front may move into the area
from the north. We expect this front to be dry, although the GFS
is trying to show some possible showers across the area. There
is a better chance of precipitation Wednesday night into
Thursday as a warm front approaches the area from the south
Wednesday night, before the occluding low pressure system moves
into the area Thursday. This will likely bring another period of
enhanced rainfall chances to the area.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...As of early morning our TAF sites are showing MVFR or
marginal IFR cigs with the continued NE surface winds.
Conditions are expected to worsen somewhat again today as
another batch of rain develops over the area. Winds should
diminish and veer to the SE later today as high pressure weakens
and moves offshore.

Tonight...Rain should move out with improving visibility in the
evening, but cigs will remain IFR or low MVFR. Winds will
become SW but generally less than 10 kt.

OUTLOOK...

Saturday-Saturday night...Conditions may improve to VFR briefly
by midday, before diminishing again to IFR by the afternoon and
evening as rainfall moves back into the area. Winds shift back
to the northeast then east during the day and continue into the
night. Moderate confidence.

Sunday...IFR conditions for the first half of the day as a cold
front moves across the area with a period of rainfall. East to
southeast winds become southwest and west behind the front.
Moderate confidence.

Sunday night...VFR conditions return. High confidence.

Monday-Tuesday...VFR. Gusty west to northwest winds 15-20 knots
during the daytime. High confidence.

&&

.MARINE...
Northeast winds have been decreasing overnight but seas remain
elevated and will be slower to subside. The SCA remains in
effect until mid/late afternoon when seas should fall below 5
ft. As high pressure moves offshore and weakens today, wind
will veer to the S by late this afternoon. Winds become SW
tonight and increase a bit, but should remain well below SCA
level.

OUTLOOK...

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

Sunday-Sunday night...Small Craft Advisory conditions likely return
to the waters by Sunday morning and conditnue through the day,
before lowering overnight Sunday night.

Monday-Tuesday...Conditions expected to remain below advisory
levels.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory until 1 PM EST this afternoon for
     PAZ054-055.
NJ...Winter Weather Advisory until 1 PM EST this afternoon for
     NJZ001.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 4 PM EST this afternoon for
     ANZ450>455.

&&

$$
Synopsis...Robertson
Near Term...AMC
Short Term...AMC
Long Term...Robertson
Aviation...AMC/Robertson
Marine...AMC/Robertson



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