Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Remove Highlighting --
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FXUS61 KPHI 191813
Area Forecast Discussion
National Weather Service Mount Holly NJ
213 PM EDT FRI AUG 19 2016
High pressure over the Appalachians will continue to build
eastward into the region today and tonight with a trough of low
pressure to our south. The high Pressure system will then move
offshore on Saturday giving way to an approaching cold front on
Sunday. This front will move through the region Sunday night with
high pressure building southeast into the region for the early and
middle parts of next week.
.NEAR TERM /UNTIL 9 PM THIS EVENING/...
-- Changed Discussion --2 PM...Sent a quick update within the past hour to put isolated
showers in the forecast thru mid afternoon across the higher
terrain of northeastern PA and northern NJ. The equipment section
of the AFD was also updated with additional radar outages to
A surface trough is forecast to develop in New England and the mid-
Atlantic this afternoon. The trough axis will likely reside
somewhere between I-95 and the coastal plain. Boundary-layer
convergence near the boundary will become better defined this
afternoon as the sea-breeze circulation advances inland and the flow
turns southeasterly to the east of the trough axis while remaining
northwesterly farther inland.
Model guidance, including the latest hires CAM models, show
convection initiating over coastal NJ and DE within the
abovementioned convergence zone during peak heating between 1 and 3
PM this afternoon. The mesoscale focus for convection will propagate
westward through the coastal plain late this afternoon and I-95
corridor this evening as the sea-breeze front moves inland. Updated
hourly PoP/Weather grids reflect this thinking. Without deeper, more
organized lift over the area today, convection should be isolated in
coverage. 12Z IAD/OKX RAOBs and model forecast soundings at
locations in our area show a mid-level subsidence inversion present
that could hinder convective growth, especially with a limited
degree of instability (MLCAPE generally less than 1250 J/kg) to tap
into. Therefore, expect the bulk of the activity this afternoon to
be showers with only a rogue thunderstorm or two.
Otherwise, we are anticipating a mostly sunny day for most of the
area. High temperatures will generally be in the mid to upper 80s
with our warmest spots in the city and Delmarva to reach 90F.
The exception to the above will be along the coast and Poconos where
highs will be in the lower 80s.
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.SHORT TERM /9 PM THIS EVENING THROUGH 6 AM SATURDAY/...
Some of the guidance is signaling the potential for isolated rain
showers continuing after dark late this evening in the Delaware
Valley. They may develop in advance of a weak impulse traveling
in the mid level flow. As a result, we will mention a slight
chance for showers at that time. Otherwise, we are expecting
scattered clouds for tonight along with a light wind. Minimum
temperatures should be in the 60s in the north and in the upper
60s and lower 70s elsewhere.
.LONG TERM /SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --Saturday and Saturday night...Weak high pressure will be in
place across the region with a trough of low pressure to our south
on Saturday. As the high pressure moves east, winds will shift to
the southeast with moisture advecting into the region from the
atlantic and gulf. Enough moisture will be in place with peak
heating to produce a few widely scattered showers and
thunderstorms during the afternoon and evening hours. It will also
be another hot day with highs pushing 90 across most of the
region. Used a blend of MET/MAV and ECMWF guidance as the overall
spread in terms on most weather elements is small.
Sunday and Sunday night...A cold front is expected to approach
the area late in the day Sunday and move into the area Sunday
night, and progress east of the region by Monday morning. Overall,
ensemble agreement is pretty good on the timing of the front.
Moisture will continue to stream northward into the region ahead
of the front allowing PW values to climb to over 2 inches. Enough
lift will be present along the front to develop showers and
thunderstorms in the afternoon and nighttime hours to our west
that then move eastward through the region. Given the good model
agreement on timing, kept pops in the likely range.
With high PW values, heavy rainfall will be a threat with most
thunderstorms. Some of the ensemble guidance is indicating a
higher likelihood for the heaviest rainfall to occur across
eastern PA into the Delmarva, as these locations are closer to the
front during peak heating hours. Some locations could see a quick
inch or even more of rainfall which could lead to some localized
flooding concerns. Used a blend of WPC/SREF and the 00z ECMWF for
qpf totals, with the overall impression the ECMWF has a better
handle on the heavy rainfall idea than the GFS and GEFS. In terms
of any severe weather, instability looks limited with 1,000 J/KG
of CAPE or less. However, modeling shows somewhat steep low level
lapse rates which could contribute to storms having some locally
strong wind gusts. For now have added heavy rain wording to the
grids and will continue mentions of heavy rain and gusty winds in
In terms of temperatures, highs have a chance to warm a few
degrees more than what MET/MAV guidance indicates given the
boundary layer temperatures still around 20C. Where sunshine comes
out highs will likely push 90 again in the Delmarva and Southern
New Jersey. highs will be cooler further northwest where the rain
arrives sooner. Temperatures will start off muggy in the 60`s to
Monday through Thursday...The front will be offshore by Monday
allowing high pressure to build southeast into the region early
next week then moves over the region for the middle part of next
week. The airmass with this high pressure system will be much
drier and cooler. High temperatures will be closer to normal with
70`s and 80`s for most of next week. Little spread in modeling and
ensemble guidance, so stuck close to WPC guidance.
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.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Conditions are forecast to be VFR through the TAF period with one
exception. Expect mainly scattered cu field with cigs between
1.5-3 kft this afternoon, increasing to 3-5 kft this afternoon.
There may be some isolated rain showers this evening, especially
in New Jersey. However, their potential is not high enough to
include in the TAFs.
A light north to northwest wind is anticipated for today. The
flow should provide limited resistance for the sea and bay breeze
fronts. The boundaries are expected to progress inland reaching
KACY, KMIV and KILG during the afternoon and early evening hours.
A light and variable wind is forecast for tonight.
Saturday and Saturday night: VFR. Can`t rule out a brief
reduction due to a stray shower or thunderstorm in the afternoon
and nighttime hours.
Sunday and Sunday night: lower than VFR conditions likely by late
Sunday afternoon with showers and thunderstorms that last into
Sunday night. Southeast winds around 15 knots, gusts around 20
Monday...VFR. Northwest winds around 15 knots with gusts around
Tuesday: VFR. Winds 10 knots or less from the northwest.
Weak surface features are expected to influence the coastal
waters of New Jersey and Delaware for today and tonight. Wind
speeds are forecast to remain generally less than 15 knots and the
direction will vary due to local influences.
Wave heights on our ocean waters will be around 2 feet and waves
on Delaware Bay should be 1 foot or less.
Friday-Tuesday... Seas will start off rather light through
Saturday night before increasing gradually from two to three feet
on Sunday. Seas may reach four feet for a time on Monday before
decreasing to around three feet on Tuesday. The highest winds will
be in association with a cold frontal boundary passing through
Sunday night. Wind gusts could push 25 knots from the southeast
late sunday before becoming northwesterly on Monday. Winds are
likely to decrease Monday night.
There is a low risk for the development of dangerous rip currents
today. The wind along the coasts of New Jersey and Delaware should
be variable this morning, then onshore in the afternoon at 10 mph
or less. A 2 foot southerly swell is anticipated.
The probable risk for the development of dangerous rip currents
is low for Saturday. However, it may approach moderate in the
afternoon with the establishment of a synoptic scale southeasterly
wind around 10 MPH.
The heat wave of the past 7 to 8 days at many locations has
This lists the number of 90 degree or warmer days (as of August
18) and the mean number of 90 degree days for each climate site
(computed from when the period of record began). We are above
normal for 90 degree days at all climate sites.
Site 90 deg days beginning of climate record
2016 mean POR
ABE 28 17 1922
ACY 26 10 1874
GED 30 27 1998
PHL 33 21 1873
RDG 30 21 1999
TTN 27 20 1998
ILG 28 20 1894
-- Changed Discussion --Due to equipment failure (A/C unit and computer), the KDIX WSR-
88D radar remains out of service. Return to service is still
unknown at this time.
Surrounding WSR-88D radars, including KDOX (Dover), KCCX (State
College) and KAKQ (Wakefield), are down with either equipment
issues or maintenance. We will use TEWR and TPHL terminal doppler
radars as well as KLWX (Sterling), KBGM (Binghamton), and KOKX
(Upton) WSR-88D radars to help fill in the radar coverage gaps as
much as possible.
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