Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 280140
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
940 PM EDT Tue Jun 27 2017

.SYNOPSIS...
High pressure over the Ohio Valley will build east across the
mid-Atlantic region through Wednesday. The high pressure will
move offshore for Thursday and Friday, returning our area to
southwest flow. Another weak cold front is expected this
weekend, bringing a chance of showers through early next week,
especially if the front stalls.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Showers that developed across parts of the area this afternoon
and evening have dissipated and outside of a very isolated
shower, we should remain dry through the rest of the overnight
period.

Skies are already starting to clear out and we should see some
drying occur as a more westerly flow is in place overnight.
Some low level moisture may linger a bit in areas where rain
fell through this evening, and some light patchy fog might
develop towards daybreak.

Light winds overnight combined with the clearing skies will
allow for good radiational cooling to take place. Already
starting to see some indication of this with 9pm temperatures
already falling in Millville (65) and Somerville (63) and
Andover (61).

Overnight lows will fall into the 50s across the region with
near 60 in the urban areas around Philadelphia and along the
coast.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
Northwest flow becomes established tomorrow on the upstream
side of the shortwave trough moving through the area tonight. A
surface high will build into the eastern U.S. This sets the
stage for a very pleasant day, with skies mostly sunny and
temperatures slightly below seasonal averages. With some fairly
pronounced mixing, winds may gust to around 20 mph or so during
the afternoon. May also see a cumulus field develop during the
day, but subsidence above the boundary layer will keep these of
the "fair weather" variety.

MOS is in generally good agreement with highs tomorrow, but low-
level cold air advection will cease during the morning, with ridging
beginning to nose into the region as the day progresses. If this
happens sooner, forecast highs may be a bit on the low side. For
now, did not stray too far from a statistical MOS blend, given the
strong consensus. Highs will be around 70 in the Poconos and near 80
southeast of the Fall Line.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
The long term starts out with surface high pressure just off
the mid-Atlantic coast and associated fairly pleasant weather.
However as the high moves farther offshore and low pressure
moves into the Great Lakes, a more typical summertime SW flow
will set up over the region. This in turn will cause increasing
heat and humidity over the forecast area through the end of the
week and into the weekend. At this point it appears that
Saturday may be the most uncomfortable day with heat indices
reaching the mid 90s along the I-95 urban corridor.

Along with more heat and humidity will be gradually increasing
chances for afternoon showers and thunderstorms. For Thursday
and Friday it looks like any precip should remain well to the
northwest of PHL. By Saturday an upper-level trof and associated
cold front are forecast to approach the mid-Atlantic and also a
surface trof is forecast to develop from eastern PA south
to near the Chesapeake Bay. Enhanced low-level convergence is
expected to result in more widespread afternoon convection on
Saturday.

For Sunday and beyond the forecast becomes more cloudy, as the
models seem to disagree on whether a surface cold front can push
through our area or whether it will stall out. Given the
uncertainty, the forecast maintains at least a slight chance for
showers/t-storms through early next week. Temperatures are
expected to be near or slightly above normal at that time.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

VFR conditions are expected to continue through the TAF period.

Overnight...Skies will clear out through tonight with light
westerly winds, less than 10 knots, across the terminals.

Wednesday...VFR conditions continue. Winds will pick up out of
the west/northwest between 14-16Z, becoming southwest around 10
knots with gusts up near 20 kts by late afternoon, Winds will
lighten as we head into the evening. Skies look to be relatively
cloud free but some cumulus may develop during the afternoon.

OUTLOOK...
Thursday and Friday...VFR conditions expected. Southwest winds
gusting up to 20 kt in the afternoon both days.

Saturday and Sunday...Mostly VFR conditions but lower at times
in scattered mainly afternoon showers and thunderstorms.

&&

.MARINE...
Sub-advisory conditions are expected through the period. Winds
should switch from southwest to northwest through the nighttime
hours, with speeds generally 10 to 15 kts with gusts to 20 kts.
Winds will switch back to southwest by afternoon tomorrow,
generally remaining around 10 to 15 kts with higher gusts. May
see gusts approach 25 kts by late afternoon, but predominantly
winds should stay below advisory criteria.


OUTLOOK...
Thursday and Friday...SCA conditions may develop Thursday
afternoon and continue into Friday due to increasing SW winds
and building seas.

Saturday and Sunday...Winds and seas are expected to be somewhat
below SCA levels.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...AMC
Near Term...Meola
Short Term...CMS
Long Term...AMC
Aviation...AMC/Meola
Marine...AMC/CMS



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