Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 242320
Area Forecast Discussion
National Weather Service Mount Holly NJ
720 PM EDT SUN JUL 24 2016
A warm front will slowly push northward through the area through
Monday morning. A cold front will approach from the west, moving
into the region late Monday night and Tuesday, then stalls near or
just to the south of the area through the midweek period. Another
system may impact the area over the weekend.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
-- Changed Discussion --A warm front will edge closer to the area overnight. A convective
system ahead of the front is rolling across west-Central Pa.
while slowly weakening. It appears that enough of the system will
remain to justify higher pops across the wrn/srn areas of the fcst
area attm. We have updated the fcst products with higher chc pops
--earlier then the previous fcst. Except for 1 tstm near KUNV, the
areas coverage of tstms seems to be less than earlier. It remain a
question what will happen when the warm and more humid air-mass
across our area interacts with the MCV.
The clouds associated with the MCS will limit our fog potential.
However, if clouds clear across our far western zones during the pre
dawn, then fog could become more widespread and/or dense toward
-- End Changed Discussion --
.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
Monday is expected to be on par with this past yesterday (Saturday,
June 23) in terms of the heat and humidity. Both this past Saturday
and upcoming Monday represent the peak of excessive heat during this
extended heatwave that started Friday and continues through late in
the week. No changes were made to the heat headlines; Excessive Heat
Warning in effect for the heat-sensitive population in the urban I-
95 corridor from Wilmington to Philadelphia to Trenton with maximum
heat indices forecast to be around 105F. To the southeast of the
warned area, including the rest of our Delmarva zones and southern
NJ, a Heat Advisory is in effect tomorrow with the heat index
peaking somewhere between 105 and 110F. Advisories are also in
effect to the north of the I-95 corridor that includes northwestern
NJ and eastern PA, where heat indices are expected to fall between
The shortwave trough associated with whats left with the overnight
MCS is forecast to move off the coast during the early to mid
morning. Model RH fields indicates the potential for mid- and high-
level clouds to hang around during the day. The clouds will play an
important role in how the forecast unfolds for Monday afternoon.
Exactly how early in the day and how persistent these breaks occur
with these leftover debris clouds will determine how hot and
unstable we get during the afternoon. Based on the latest guidance.
we think subsidence in wake of this early morning shortwave will
provide an opportunity for most of the area to at least partially
clear out by late Monday morning. Strong heating will allow for
temperatures to rise quickly into the 90s during peak heating hours
and for the atmosphere to rebound/destabilize.
A pre-frontal surface trough is forecast to sharpen on the lee side
of the Appalachians during the day. Convection will likely initiate
during the first half of the afternoon to our west near the lee
trough and also to our north with deeper lift arriving in advance of
an upper shortwave disturbance moving over the Great Lakes. This
activity is then expected to progress eastward late in the day. The
greatest confidence in showers and storms (and thus highest PoPs)
arriving before the short term period ends is north and west of the
fall line. A slight chance of showers and storms are forecast for
Philadelphia between 4 and 6 PM. The latest D2 outlook from SPC
includes northeast PA and northwest NJ in a slight risk for severe
storms. The marginal risk for severe storms farther southeast into
the I-95 corridor though the bulk of thunderstorm activity may
still be upstream of Philadelphia through 6 PM. The main threats
with these storms will be locally damaging winds. Storms that form
in such a hot and very humid airmass (e.g., yesterday) tend to
produce severe thunderstorm episodes. Although the amount of
instability Saturday should be similar to yesterday (MLCAPE 1500-
2500 J/kg), DCAPE values may be slightly less tomorrow with not as
pronounced mid level drying. The other concern will be locally
heavy rainfall that could result in flash flooding as storms develop
in a moisture-rich environment (PWATS exceed 2) and a slow-moving
boundary approaching to our west.
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Showers and thunderstorms are expected Monday night into Tuesday as
the cold front makes its way into the area. The cold front stalls as
it moves south and looks to remain in the vicinity of Delmarva
through the midweek period. Areas that manage to stay behind the
stalling boundary will have some cooler and drier air moving in,
which will allow for the hot and stickiness of the past several days
to finally decrease. While it will still be fairly hot outside,
those lower dewpoints will help us to remain at a more comfortable
level and we do not anticipate any headlines will be needed at
this time. Areas closer to the stalled boundary will remain a bit
more humid and will continue to have a chance for showers and
The front will waver and start to push northward as a warm front
late Wednesday or Thursday. Showers and thunderstorms will remain
possible in areas closer to the boundary. The front will also serve
as transport for a few waves of low pressure, which will move fairly
quickly through the area. Overall, showers and thunderstorms will be
a threat from midweek through the weekend.
.AVIATION /23Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
VFR through midnight. Scattered showers and isolated thunderstorms
are expected to move in from the west during the early overnight
possibly lasting as late as the early morning. A 3-4 hour tempo
group for shra and MVFR restrictions were included at each TAF
site. Confidence in thunder and potential for lower restrictions
was too low to include with the 00Z TAFs.
South to southwest winds around 10 knots will become light and
variable winds tonight. SW winds 5-10 kt Monday morning become
more westerly toward midday and the afternoon. Showers and
thunderstorms may reach ABE-RDG during the mid to late afternoon
Monday. This activity will likely remain upstream of the I-95 TAF
sites through 23Z.
Monday night through Friday...Mainly VFR conditions expected.
Scattered showers and thunderstorms on Monday and Wednesday
through Friday, with MVFR/IFR conditions possible at times.
-- End Changed Discussion --
Sub-small craft advisory conditions will continue tonight and
Monday. There is a chance of showers and a slight chance of
thunderstorms late tonight into the first half of Monday morning.
Additional showers and storms will likely remain inland through the
afternoon on Monday.
Monday night through Friday...Sub-advisory conditions are expected
to continue on the area waters through much of the week. Expect
higher winds and waves in and near scattered showers and
thunderstorms, mainly Monday night into Tuesday and again on
Wednesday through Friday.
Rip Currents....The risk for formation of dangerous rip currents is
low today. The setup for rip currents is better on Monday with a
strengthening SW flow during the day but it will likely still be in
low risk category.
The forecast high temperature for Philadelphia tomorrow, Monday,
July 25th, is currently 98F. The last time the temperature
reached or exceeded 98F at PHL was three years ago on July 18,
2013. The last 100-degree day at PHL occurred four years ago on
July 18, 2012.
Record high temperatures for Monday through Thursday are below. We
may tie or break daily record highs tomorrow at several of our
Site 25th 26th 27th 28th
---- ---- ---- ---- ----
PHL... 96-1899 101-1892 101-1940 100-1941
ABE... 95-1999 98-1940 98-1955 97-1949
ACY... 99-2010 96-2011 99-2005 98-1999
ILG... 96-1987 99-1894 100-1894 101-1894
TTN... 97-1999 99-1892 100-1894 101-1894
GED... 99-2010 97-2012 98-2005 99-1949
RDG... 96-1999 99-1940 98-1955 99-1941
MPO... 90-1999 89-1949 91-1955 93-1949
PA...Heat Advisory from 11 AM to 6 PM EDT Monday for PAZ060>062-101-
Excessive Heat Warning until 6 PM EDT Monday for PAZ070-071-
NJ...Heat Advisory from 11 AM to 6 PM EDT Monday for NJZ001-007>010-
Excessive Heat Warning until 6 PM EDT Monday for NJZ015-
DE...Heat Advisory from 11 AM to 6 PM EDT Monday for DEZ002>004.
Excessive Heat Warning until 6 PM EDT Monday for DEZ001.
MD...Heat Advisory from 11 AM to 6 PM EDT Monday for MDZ008-012-015-