Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 270143
Area Forecast Discussion
National Weather Service Mount Holly NJ
943 PM EDT TUE JUL 26 2016
A weak cold front will continue to slowly drift south across the
region overnight before stalling nearby to our south Wednesday
into Thursday. Several waves of low pressure developing along this
boundary will result in periods of showers and thunderstorms late
in the week and this weekend.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
The weak cold front is more tough to find now that the winds are
light to locally calm. Now that the mixing has waned, the dew
points have increased some for much of the area. The exception is
portions of the Poconos. The leftover boundary looks to remain in
our vicinity overnight.
All the convection remains to our southwest so far where
instability is greatest and some short wave energy is moving
eastward. Prior to losing the visible satellite imagery for the
day, there appeared to be a convectively induced short wave
cresting the Appalachians of West Virginia to western Maryland.
This feature moved out of southern Ohio earlier. The forecast
challenge is does this feature develop some convection across our
southern areas well after Midnight. The HRRR and RAP show some
development after about 06z in the Philadelphia metro. The model
guidance generally show dew points and elevated instability
increasing overnight across mainly the southern zones. This is low
confidence and therefore we maintained mostly slight chance pops
from about northern Delaware southward overnight.
Otherwise, some increase in high to eventually some mid level
clouds across at least the southern half of the area. Across the
northern areas especially for awhile, radiational cooling and some
lower dew points and very light winds has allowed the temperatures
to drop a bit faster. Patchy fog may develop before sunrise across
northeastern PA and northwestern NJ.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
Some of the model guidance shows the cold front moving south of
Delaware Wednesday morning while others keep the front stalled over
our southern zones. Given it`s the middle of the summer and zonal
steering flow aloft, we favor a more northern solution with the
front stalling in the Delmarva. Expect additional showers and storms
to develop along the lingering boundary during peak heating hours
Clouds near the front will likely keep temperatures down a few
degrees in DE and eastern MD (upper 80s) while stronger heating
under mostly sunny skies in eastern PA and NJ will allow for
temperatures to climb back into the 90s. However, we are looking at
low 90s for highs and humidity levels will be comfortable with
dewpoints in the 60s.
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
The front will remain fairly stationary over the Delmarva
Wednesday night into Thursday before starting to push back north
as a warm front Thursday night into Friday. This boundary will
act as a focus for weak low pressure development. These waves will
then ride along the boundary and will result in a flare-up of
showers and thunderstorms. Specific timing for this can be tricky
and subject to change, but current thinking is for Thursday night
into early Friday and then again on Saturday. Outside of these
times, expect generally diurnal driven climatological threat of
showers and thunderstorms.
After a bit of a reprieve with lower humidity levels mid-week, dew
points will increase back to 70-75 over the Philadelphia metro
area, southern New jersey and the Delmarva by Thursday and
Thursday night. This will push the heat index values into the
upper 90s, almost 100 on Thursday. After that, expect lower heat
indices for Friday and the weekend as high temperatures will be
suppressed by increased cloud cover.
It appears that the weather will remain warm, muggy and unsettled
through the start of the next week, before the frontal boundary
finally sinks far enough south to allow a marginally cooler, but
drier airmass the infiltrate the entire region.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Mainly VFR through Wednesday. Patchy fog may develop late tonight
in the fog-prone terminals (e.g., RDG, MIV). There could be a
shower or thunderstorm well after Midnight near ILG and perhaps
to PHL, however this is of low confidence. Showers and storms
Wednesday afternoon are expected to stay south of the terminals
(but it will could be very close by to ILG- MIV- ACY).
Light and variable winds tonight, however locally southwest for
awhile especially at PHL and ILG. The winds generally west-
northwest 5-10 knots on Wednesday but the sea breeze will likely
result in a wind shift out of the south- southeast at ACY and MIV.
The sea breeze front could make it to the I-95 terminals toward
Wednesday night through Sunday...Mainly VFR conditions expected.
Scattered showers and thunderstorms Thursday, Friday and Saturday,
with MVFR/IFR conditions possible with any shower and thunderstorm
The winds are expected to turn around toward the north late
tonight especially across the northern and central zones as a
weak front moves southward. The winds should then turn southerly
Wednesday afternoon as a sea breeze develops. Speeds should
remain under 20 knots. Wave heights on our ocean waters are
expected be 2-3 feet through the period. Waves on Delaware Bay
should be 2 feet or less.
Wednesday night through Sunday...Sub-advisory conditions are
expected to continue on the area waters through the forecast
period. Expect higher winds and waves in and near scattered
showers and thunderstorms that will be more likely at the end of
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 Wednesday and Thursday are below.
Site 27th 28th
---- ---- ----
PHL... 101-1940 100-1941
ABE... 98-1955 97-1949
ACY... 99-2005 98-1999
ILG... 100-1894 101-1894
TTN... 100-1894 101-1894
GED... 98-2005 99-1949
RDG... 98-1955 99-1941
MPO... 91-1955 93-1949