Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 211952
Area Forecast Discussion
National Weather Service Mount Holly NJ
352 PM EDT THU JUL 21 2016
High pressure remains south and east of the area tonight. A weak
cold front is expected to move across the region Friday night
into early Saturday. Strong high pressure will then build in
before another cold front moves through early next week. High
pressure should then briefly build back into the area Wednesday.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Its been an excellent summer day...a few cumulus and winds generally
under 15 mph with a few southwest gusts 15-20 mph on the interior
near and west of I-95 while a strengthening southerly sea breeze
is now developing along the coasts with gusts 20-25 mph possible
by 5 PM. Relatively low humidity.
By 5 PM we should have Day 1 of what will probably be quite an
extended and notable heat wave beginning this afternoon at
Tonight...Fair skies and a bit milder, in part due to a south to
southwest breeze, a rising dewpoint and maybe some southeastward
moving cirrus debris from the sewd moving Great Lakes
Forecast basis is generally a 50 50 blend of the 12z/21 GFS/NAM
.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
Mostly sunny, hot and humid with a southwest wind gusting 15-20
mph during the afternoon. Should reach 95-96F in Philadelphia
Friday afternoon (4C warmer at 850 mb) and dewpoints around 5F
warmer during the afternoon as compared to the upcoming upper 50s
values of this afternoon. The result will be a max HI around 98-99F,
possibly 100F for an hour. We may eventually need to issue an
advisory for Friday afternoon, prior to the higher impact anticipated
need for a Excessive Heat Warning this weekend.
Thunderstorm risk?: It appears a 700mb Temperatures cap of 10C
develops during the afternoon so while we cant rule out tstms...
it appears if any occur...they should be confined near or N of
I-78...roughly KPTW- KMJX northward and late afternoon, if then.
It may be that they develop and move rapidly sewd near 00z/23?
Will add gusty winds to the thunder fcst for late Fri. PWAT 1.7"
so if it thunders, rain will be briefly heavy with usual poor
drainage street flooding. Its conditional on tstms developing
which is the uncertainty.
Forecast basis was generally a 50 50 blend of the 12z/21 GFS/NAM
mos guidance, favoring the warmer GFS with support from the 2m
temps of the 12z/21 NAM and ECMWF.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Hot wx is expected for the extendd pd. A wk cdfnt will be working
its way thru the area Fri night and will bring some shwrs/tstms
with it. The best chcs are up north and gusty wind and hail look
to be the main threats. Precip chcs shud be mainly erly.
Once this front crosses the area, high pres will build in. Sat
looks to be very hot and humid, with heat index values between 100
and 105 degrees.
Sunday and Monday, there looks to be some disagreement in the
mdls. It still looks hot, but the GFS has backed off a bit now on
Sun. The ECMWF is a bit warmer with temps on Sun, but dew points
are still lower. Mon dew points differ by 4 to 5 degrees and temps
do as well and that can make a big difference. Based on the
uncertainty, have opted to leave the excessive heat watch up for
Another cdfnt will cross the area later Mon bringing shwrs and
tstms. Then it will be slightly cooler and less humid behind the
front for the remainder of the week. However, it is very likely
that from tomorrow thru at least Wednesday of next week we will
have temperatures above 90 degrees and we could have several days
with temps in the mid and even upper 90s.
.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Rest of today...VFR sct cu aoa 6000 ft. A sw wind generally under
10 kt except south southeast bay and sea breezes from vcnty KACY
to KMIV and KILG this afternoon.
Tonight...VFR. Possible MVFR haze fog at a few taf sites near
09z/22 but confidence below average on any vsby restriction.
Friday...VFR sct clouds aoa 5000 ft. A sw wind gusty 15-18kt during
the afternoon. Small chc of a sewd moving gusty tstm (35kt) vcnty
krdg/KABE/KTTN near or after 21z. Confidence: below avg on
Fri night...Generally VFR. A chance of shra/tsra which may
briefly lead to MVFR/IFR. Gusty southwest winds 15-20 knots.
Moderate to high confidence, below average on mvfr/ifr.
Saturday-Sunday...VFR. High Confidence.
Monday-Monday night...Generally VFR. A chance of showers and
thunderstorms which may briefly lead to lower conditions.
Gusty southwest winds 15-20 knots.
Southerly winds will gust just above 20 kt late this afternoon
and evening along the northern NJ coastal waters, but are expected
to remain below SCA criteria at this time. Seas should generally
be 3 ft or less. Caped any gusts at 24 kt.
Friday...a south-southwest wind gusty to 20 to possibly kt during
the afternoon. No SCA attm since confidence on wind above 22 kt
is below average at this time (attm). capped late Fri gusts at 24
kt for the time being.
Fri night...SCA conditions psbl with increasing winds ahead of an
approaching cdfnt. However, confidence is low due to very warm air
over cooler waters, so nothing issued attm.
Sat-Tue...Sub-Small Craft Advisory conditions expected.
RIP CURRENTS...There should be a developing moderate risk for the
formation of dangerous rip currents along the central and northern
NJ shore this afternoon, due to increasing southerly sea breezes
and heading into low tide. Elsewhere, only a low risk.
The probable risk for the formation of dangerous rip currents
Friday is moderate along the NJ shore from Atlantic County
northward and low for the Delaware Beaches and Cape May county.
Confidence on how much southerly component is a little below
average so the moderate risk may end up low enhanced.
Looking further ahead, with the Atlantic Basin still devoid of
tropical storms, the risk for the formation of dangerous rip
currents should be Low.
Next Monday the 25th, we might have enough wave height to around 4
feet and water buildup due to southerly winds, to have a more
widespread low enhanced or even moderate risk but confidence on
seas building that high is below average.
Water temperatures have rebounded after the massive upwelling
event associated with the squall line passage late Monday. Water
temps today were in the low to mid 70s, above normal for this
time of year and quite a rebound from the lower 60s of Tuesday.
Colder upwelling might develop again late Friday or Saturday.
Near record (within 2f) or record warmth is anticipated for many
sites on 1 or 2 days of the following listed.
23rd 24th 25th 26th
PHL 101-2011 98-2011 96-1899 101-1892
ABE 99-1955 95-1999 95-1999 98-1940
ACY 105-2011 100-2011 99-2010 96-2011, 1963
ILG 100-2011 98-2011 96-1987 99-1894
TTN 104-2011 98-1910 97-1999 99-1892
GED 104-2011 99-2011 99-2010 97-2012
RDG 100-2011 96-2010 96-1999 99-1940
MPO 91-1955 91-1914 90-1999 89-1949
PA...Excessive Heat Watch from Saturday morning through Sunday
afternoon for PAZ060>062-070-071-101>106.
NJ...Excessive Heat Watch from Saturday morning through Sunday
afternoon for NJZ007>010-012>027.
DE...Excessive Heat Watch from Saturday morning through Sunday
afternoon for DEZ001>004.
MD...Excessive Heat Watch from Saturday morning through Sunday
afternoon for MDZ008-012-015-019-020.