Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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199
FXUS61 KPHI 261703
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
103 PM EDT Wed Apr 26 2017

.SYNOPSIS...
The coastal low that has affected the East Coast the past
several days will begin pulling away from the region today, but
will be slow to exit. A cold front will move across the area
Thursday night, with a second Saturday night. A warm front is
expected to lift across the area Sunday night, followed by
another cold front on Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
1230 PM ESTF: cloudy with areas of drizzle and isolated showers
spinning west and southward through the forecast area into this
afternoon due to the close proximity of the vertically stacked
low pressure system off the mid Atlantic coast.

VERY few changes to the 330 am fcst temps/dews.

From the 330 AM fcst discussion for temps today.

Model guidance continues to show considerable spread regarding
temperatures today. MOS guidance from the MAV (highs in the 70s)
is 5-10F warmer than the MET (highs in the 60s) due to
differences in how much sunshine develops this afternoon. There
does not appear to be a notable mechanism to mix out the marine
stratus today with a strong low-level inversion remaining in
place, light N-NEly winds and no notable source of dry/cold air
advection. Accordingly, forecast weighted more toward the cooler
and cloudier NAM-based guidance though not quite as extreme. If
breaks in the clouds were to develop this afternoon, forecast
temperatures would need to be adjusted upward by several degrees
(which would be more likely to occur farther inland toward the
eastern shore of MD and our far western zones in eastern PA).

Tonight...The coastal low will continue to weaken tonight as it
moves out to sea, passing south of Long Island/southern New
England. Marine moisture will remain trapped underneath the
subsidence inversion. Any stratus that mixes out this afternoon
should redevelop quickly after dark tonight. At least patchy fog
is anticipated late this evening and overnight, but the extent
of the fog should be limited by the presence of stratus
beforehand. It should be noted that some of the guidance shows
dense fog forming late tonight but we have not quite bit on that
due to the previously mentioned reasons. Cloud cover should
curb how much cooling takes place tonight. Forecast lows are in
the 50s. Nearly calm wind.

&&

.SHORT TERM /THURSDAY/...
On Thursday, our area will be under the influence of return flow
ahead of an approaching cold front. Brighter...especially south
of I78 during the afternoon. Still a lot clouds. warmer. Wind
becomes southeast to south.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
It is possible that an isolated shower may develop across
northeast Pennsylvania and northern New Jersey as a weak short
wave/vorticity impulse approaches the area. However, the best
chances for rain are expected to be during the overnight hours
as the front moves across the area and a stronger short
wave/vorticity impulse moves across the area. Although much of
the guidance dissipates the more widespread showers as they
approach, they do keep some scattered showers across our area.

The front moves offshore Friday morning and any showers will
dissipate and/or move offshore through the morning as well. The
remainder of Friday will remain dry as weak high pressure
briefly affects the area.

By Friday night, another frontal boundary is forecast to begin
approaching the area from the north as it crosses Pennsylvania
and New York. The front will cross through the area during the
day Saturday, then stall to our south Saturday night into
Sunday. There is some slight timing differences in the model
guidance on when the front moves through. But as a couple of
short wave/vorticity impulses move across the area Friday night
through Saturday night, there will be a chance for
isolated/scattered showers.

The front will stall to our south during the day Sunday, which
should allow Sunday to be dry. Being the front is a back- door
front coming from the north, it will bring cooler conditions on
Sunday. But the front will not stay to our south very long as it
is expected to lift back northward as a warm front Sunday
night/Monday morning. While there is a chance of showers Sunday
night into Monday morning, the more likely time period for any
precipitation would be later Monday into Monday night as a cold
front approaches from the west. Being we should enter into the
warm sector during the day, we should warm quite nicely, and in
turn some instability should build ahead of the front. Therefore
there will be a chance of thunderstorms Monday afternoon and
Monday night.

The front will move offshore by Tuesday morning, but a
secondary surface trough may move across the area during the day
Tuesday. With a short wave/vorticity moving across the area
during the day, there could be some isolated showers across
northeastern Pennsylvania and northern New Jersey.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Rest of this afternoon...Cigs 800 to 1800 feet continue to improve-
rise with a few remaining patches of IFR drizzle, mainly NNJ.
Probably goes MVFR to possibly VFR cigs by 22z most everywhere.
Light northeast wind.

Tonight...IFR conditions in st/fog should redevelop in nearly calm
wind though it may take until near 06z for IFR to redevelop at
the inland sites, dependent on how warm it gets there late this
afternoon.

Thursday...Ifr or MVFR conds in st/fog to start the day, probably
improves to VFR sct-bkn clouds aoa 3500 feet during the
afternoon. Wind becoming southeast to south.


OUTLOOK...

Thursday night...Generally VFR. A chance of showers overnight
which could temporarily reduce conditions to MVFR.

Friday...VFR conditions expected.

Friday night...VFR early. Patchy fog and low CIGS may develop
overnight.

Saturday...Becoming VFR during the morning, then a chance of
showers during the afternoon. Conditions may temporarily be
reduced with any showers.

Saturday night-Sunday...Low clouds and fog may develop
overnight Saturday and continue into Sunday leading to reduced
conditions. There will also be a chance of showers.

&&

.MARINE...
The Small Craft Advisory hazardous seas continues through
Thursday. Waves are currently around 7-9 ft and will gradually
subside to 4-7 ft late this afternoon and tonight.

OUTLOOK...

Thursday night...Small Craft Advisory for hazardous seas
through Thursday night.

Friday...Winds expected to remain below advisory levels, but
seas may remain elevated to advisory levels.

Friday night-Sunday...Winds are expected to remain below
advisory levels. Seas may approach 5 feet at times, but mostly
remain around 4 feet.

&&

.TIDES/COASTAL FLOODING...
We will continue to monitor the high tide this evening since it
will be the higher one that occurs with a new moon. If the water
does not drain away from the coast fast enough, we could see
some localized minor flooding at that time. ETSS and a few of
the higher NYHOPS ensemble members predict levels reaching minor
threshold (but below local advisory criteria) at Lewes, Cape
May and Reedy Point while the majority of the remaining guidance
(including ESTOFS) keeps it short of minor.

&&

.CLIMATE...
Presuming our forecast temps these last 5 days of April are accurate,
we are assured of a top 3 warmest April on record in much of our
forecast area. Sunday is the critical day for determining record
or not.

Below: April projected within the top April avg temps, the
normal for April and the period of record (POR).

PHL normal 54.0 POR 1874

59.4 1994
59.2 2017?
58.5 1921
58.4 2010
57.9 1941

ABE normal 49.9 POR 1922

56.6 projecting record
56.4 1941
54.7 1994

ACY normal 51.7 POR 1874

57.2 projecting record
56.3 2010
56.1 2011

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory for hazardous seas until 6 AM EDT Friday
     for ANZ450>455.

&&

$$
Synopsis...Robertson
Near Term...Drag/Klein 103
Short Term...Drag/Klein
Long Term...Robertson/Miketta
Aviation...Drag/Robertson 103
Marine...Drag/Klein/Robertson 103
Tides/Coastal Flooding...
Climate...



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