Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Remove Highlighting --
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FXUS61 KPHI 210936
Area Forecast Discussion
National Weather Service Mount Holly NJ
536 AM EDT SUN AUG 21 2016
A cold front extended from eastern Ontario across Ohio to the
lower Mississippi River Valley early this morning. The front will
progress eastward and it is forecast to pass through our region
this evening. High pressure is expected to follow for much of the
new week. A cold front is anticipated to approach from the
northwest on Friday and it should arrive on Friday night. Another
area of high pressure is expected for next weekend.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Any fog early this morning should burn off around sunrise.
A cold frontal boundary located from the eastern Great Lakes into
the southeast states will continue moving eastward and into our
region today. Also, a warm front across Virgina will lift
northward through the region this afternoon. The winds and flow
ahead of this front will continue to be from the southeast
allowing even more moisture to advect in.
Both fronts will likely serve as lifting mechanisms for the
development of showers and thunderstorms to our west that then
move through our region in the afternoon hours. The abundance of
moisture is shown in the modeled PW values of over 2 inches along
with a deep moist layer in modeled soundings. Both of the aspects
support the likelihood for heavy rainfall with thunderstorms that
move through, maintaining hvy rain wording in the products.
In terms of any thunderstorms becoming severe, both the
instability and shear reflect a more marginal possibility. Modeled
CAPE values are around 1,000 J/KG in the afternoon with modestly
steep low level lapse rates. However, a lack of dry air in the
sounding is present as well. While a few thunderstorms with strong
or damaging wind gusts can not be ruled out it is a more limited
threat than that of heavy rainfall at this time. Northern parts of
our region will be near the triple point (intersection of fronts),
modeled helicity values particularly on the NAM 00z run increase
in the lowest 1KM of the sounding (over 100 m2/s2). Some turning
of winds near the surface and looping in the hodographs are
present as well. These aspects of the sounding data suggest a
tornado can not be ruled out from the Lehigh Valley into northern
NJ. This possibility wains quickly further south away from the
expected position of the triple point.
Showers and thunderstorms will start to end from west to east as
the cold front enters the picture. Many spots could pick up a
quick inch or even more of rainfall leading to ponding of water on
roads and other localized flooding issues. Outdoor plans have the
highest chance of being rain free in the morning with chances
going downhill by early afternoon west of Philly and mid afternoon
Temperatures yesterday ended up a few degrees warmer than
MAV/MET, so we have gone in this direction again for areas that
will see some sunshine throughout most of the day. These spots are
from Philadelphia and points to the southeast where highs will be
near 90 with 80`s further NW. Momentum transfer in the sounding
also shows the potential for some wind gusts near 20 mph in the
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
The cold front will quickly plow eastward through the region
during the evening. A gradual clearing trend from west to east
will come in behind the front. Lows should drop into the 60`s for
most locations. Any lingering showers/storms near the shore will
end in the early evening.
.LONG TERM /MONDAY THROUGH SATURDAY/...
High pressure is forecast to be located over the Ohio River
Valley on Monday. The air mass will build eastward with its center
expected to settle over or near our region for Tuesday and Tuesday
night. As a result, we are anticipating a mostly clear sky and low
humidity for the period from Monday through Tuesday night. Maximum
temperatures should favor the 70s up north and the lower and
middle 80s elsewhere. Overnight low are expected to be mainly in
the 50s except in urban areas and along the coast where minimum
readings will likely be in the 60s. A clear sky and light wind may
allow for the development of late night river valley fog across
parts of eastern Pennsylvania and northern New Jersey, an early
sign of the coming autumn.
The center of the high is forecast to pass off the coast on
Wednesday before moving out to sea. Our region should be in the
southerly return flow on the back side of the high late in the
week with a gradual increase in both heat and humidity
anticipated. Maximum temperatures may again approach 90 in our
central on southern counties on Friday.
No precipitation is expected for Wednesday and Thursday. However,
the model guidance continues to bring a cold front from the
northwest toward our region on Friday with the boundary arriving
on Friday night. We will continue to mention a chance of showers
and thunderstorms with the front.
.AVIATION /10Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
An occasional scattered to broken deck around 2,500 feet has been
present over the last several hours. This will likely persist for
a few more hours before lifting around sunrise. With light winds,
some patchy fog has formed impacting KMIV now. This may spread to
a few other terminals toward sunrise but would burn off fairly
VFR conditions are expected throughout the morning after any fog
burns off. However, Showers and thunderstorms in the afternoon
will lead to ceiling and visibility restrictions moving in from to
west across the region. Start times at KRDG and KABE will be
closer to 18z, while at PHL 20z looks to be a more reasonable
start time and a couple of hours later at KACY. Showers and
thunderstorms should last a few hours at any given location with
clearing starting to take place by evening. Some wind gusts of
15-20 knots from the southeast are possibile in the afternoon
hours as well. VFR conditions tonight with winds shifting to the
west and northwest around or just under 10 knots.
Monday through Thursday...Mainly VFR.
Wave heights are expected to increase gradually throughout the
day reaching three feet in the afternoon and evening hours.
Southeast wind gusts from 15-20 knots are likely in the afternoon
ahead of a cold front. Both the seas and winds are expected to
continue a slight ramp up toward sunrise Monday with the passage
of a cold frontal boundary. An SCA starts at 5am Monday for the
increased seas and winds.
Monday...Northwest wind gusts around 25 knots are expected. A
Small Craft Advisory is in effect until 11:00 AM Monday for our
coastal waters from around Atlantic City southward and for
Delaware Bay. The Small Craft Advisory is in effect until 5:00 PM
Monday for our coastal waters north of Atlantic City.
Monday night through Thursday...No marine headlines are
Wind gusts from the southeast in the afternoon coupled with wave
heights around three feet will allow conditions to be more
representative of a moderate risk day across the New Jersey
beaches. These conditions yield a lower risk for the Delaware
The probable risk for the development of dangerous rip currents
on Monday is low. A northwest wind is expected.
MARINE...Small Craft Advisory from 5 AM to 11 AM EDT Monday for ANZ430-
Small Craft Advisory from 5 AM to 6 PM EDT Monday for ANZ450-