Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 232011
Area Forecast Discussion
National Weather Service Mount Holly NJ
411 PM EDT SAT JUL 23 2016
A very weak front will cross Delmarva this evening. High pressure
will build over the area later tonight and through the day Sunday. A
weak cold front will cross the region Monday. High pressure will
return for the middle part of the week. Another front may affect the
area Thursday and Thursday night.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Surface low pressure was over the Canadian Maritimes this afternoon.
A cold front extends southwestward from the low into downeast Maine
and then westward along the I-90 corridor of the Northeast states.
Meanwhile, a pre-frontal trough was analyzed over the mid-Atlantic
region. The surface trough was positioned over the coastal plain in
southern NJ, stretching to the west into far southern PA. Dewpoints
were in the low 70s with a west-southwest wind south of the
boundary. Meanwhile north of the boundary, gusty northwest winds
have resulted in much drier air mixing down to the surface with
dewpoints in the 50s and lower 60s north of Philadelphia. The
surface trough will sharpen over the next few hours, but it is not
expected to move much through sunset. The cold front to our north
will eventually catch up with the pre-frontal trough later this
evening. The front should then dissipate as it moves south of the
Made only minor edits to the hourly PoP and Wx grids for the rest of
the afternoon and tonight. Isolated to widely scattered showers and
thunderstorms are anticipated along and south of the surface trough.
There could be an uptick in coverage late this afternoon as
additional lift from an upper shortwave trough passes nearby to our
north. As mentioned in the previous discussion, added enhanced
thunderstorm wording (gusty winds and hail) for far southern PA and
NJ as well as eastern MD and DE through mid evening. The latest
mesoanalysis shows a moderately unstable airmass along and southeast
of the surface trough with MLCAPE values already 2000-2500 J/kg
across the southern third of the CWA. High values of DCAPE off SPC
mesoanalysis indicate a favorable thermodynamic environment for
locally strong convective wind gusts via wet microbursts given how
moist the boundary layer is and dry the column is above it. The
threat of severe weather should start to wane after sunset. There
could be an isolated storm or two lingering after midnight toward
the lower Delmarva.
The Excessive Heat Warning continues for the urban I-95 centers of
the greater Philadelphia metro where heat indices are currently in
the 97-103F range this afternoon. Same goes for the Heat Advisory
farther east into central/ southern NJ where heat indices are
currently in the 97-103F range and farther south into eastern MD and
DE where it is the 100-109F range.
Low temperatures range from the mid 60s in northeast PA and
northwest NJ to mid 70s in the urban areas and the coastal plain.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
The cold front will move south of the area by morning. The airmass
will be only slightly cooler behind the front. In northeast PA and
northwest NJ, where CAA is a bit more robust high temperatures will
be about 3-5 degrees lower than today. Farther south, expect only a
1-3 degree difference between tomorrow and today. However, drier air
will works its way into the region behind the cold front, so it
shouldn`t be too humid outside of the southern DE and adjacent
eastern MD (where dewpoints will still be around 70F).
Forecast soundings show a subsidence inversion that should cap
convection with us located underneath the ridge. The forecast was
kept dry accordingly. Winds will be light and variable through the
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
No huge changes foreseen in the summer-like pattern with upper
heights remaining high across much of the U.S. The storm track will
be across southern Canada with short waves and weak low pressure
systems moving across the area. The weakening cold fronts associated
with these features will cross the area thru the week. The best chc
for showers and tstms will center around both Mon and Thu. We have
kept pops in the chc range for these periods with mostly dry or slgt
chc pops for other periods. The exact timing will depend on the
individual waves which the models have difficult resolving by the
end of the extended period. Pretty much all of the major models have
precip somewhere across the area Monday. SPC has a marginal risk for
SVR storms across much of area then.
The above normal temperatures will continue thru much of the week.
Monday will likely be the hottest day with readings in the mid/upper
90s and heat index values in the 100s. The temperatures and dew
points will be lower for Tue and Wed, but still in the
uncomfortable/marginally unsafe range with heat index values 95-100
over the urban areas.
.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Predominately VFR thru Sunday. However, isolated showers and
storms from PHL southward could result in brief/localized
restrictions to MVFR or IFR between about 20 and 00Z.
Some patchy fog may develop across mainly the southern portions of
the area later tonight, especially if any precipitation falls at any
of the terminals.
W-NW winds will continue to gust to 20 kt this afternoon before
becoming light and variable tonight. Winds AOB 10 kt on Sunday.
VFR much of the time. Scattered (mostly) late afternoon and
evening showers and thunderstorms may limit cigs/vsbys at times
through the period.
Winds have backed out of the SW and even S in spots this afternoon.
S-SWly winds will be strongest late this afternoon and early evening
in our coastal waters off S NJ and DE. Winds could be sustained near
20 kt but the potential to mix down higher gusts is minimal with a
hot airmass residing over the relatively cooler waters. While there
could be a few gusts near 25 kt late in the day nearshore, do not
expect conditions will warrant a SCA.
Winds will be light tonight and Sunday with high pressure building
Medium-period sly swells will persist today and tomorrow. Wave
heights should subside in the 2-3 ft range through the remainder of
Mostly a period of sub-sca conditions expected. scattered showers
and thunderstorms will create locally higher winds and seas
through the period.
Record high temperatures today through Thursday are below.
Site 23rd 24th 25th 26th 27th 28th
---- ---- ---- ---- ---- ---- ----
PHL... 101-2011 98-2011 96-1899 101-1892 101-1940 100-1941
ABE... 99-1955 95-1999 95-1999 98-1940 98-1955 97-1949
ACY... 105-2011 100-2011 99-2010 96-2011 99-2005 98-1999
ILG... 100-2011 98-2011 96-1987 99-1894 100-1894 101-1894
TTN... 104-2011 98-1910 97-1999 99-1892 100-1894 101-1894
GED... 104-2011 99-2011 99-2010 97-2012 98-2005 99-1949
RDG... 100-2011 96-2010 96-1999 99-1940 98-1955 99-1941
MPO... 91-1955 91-1914 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 NJZ007>010-
Heat Advisory until 8 PM EDT this evening for NJZ012>014-016-
Excessive Heat Warning until 6 PM EDT Monday for NJZ015-
DE...Heat Advisory from 11 AM to 6 PM EDT Monday for DEZ002>004.
Heat Advisory until 8 PM EDT this evening 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-
Heat Advisory until 8 PM EDT this evening for MDZ008-012-015-