FXUS61 KPHI 141420
Area Forecast Discussion
National Weather Service Mount Holly NJ
1020 AM EDT Tue Aug 14 2018
A frontal boundary will remain along the coasts of New Jersey and
Delaware today before drifting off the coast and dissipating
tonight into Wednesday. Low pressure is anticipated to pass
across the southern and eastern Great Lakes on Thursday and
Friday. The low is forecast to move through northern New England
on Friday night at which time it should pull a cold front into
our region. The boundary may stall over the weekend before
pushing southward on Monday.
.NEAR TERM /UNTIL 9 PM THIS EVENING/...
930 AM update...Focus on updates to the forecast was to provide
more timing/location details with the showers and storms today
(edited hourly PoP and weather grids). This is no easy task as
convection will be likely be loosely organized and there will
be multiple rounds of it. There are many potential lifting
mechanisms to focus convective development today, including
(1) several weak shortwave disturbances aloft pivoting around
the backside of the upper low that is moving eastward across the
southern tier of NY state, (2) differential heating boundary
along the edge of the denser stratus deck that formed this
morning near the Delaware Valley, (3) a surface trough over the
coastal plain, and (4) a trailing cold front that should jump
eastward toward the pre-frontal surface trough.
Pondered issuing another Flash Flood Watch for the area today
given the numerous rounds of excessive rainfall over the past
month (including yesterday's) has resulted in saturated soils
and swollen streams, making our region highly prone to
additional flash flooding. Rainfall rates as little as 1" in an
hour may be enough to produce more flash flooding. Luckily,
storms will be moving much faster than today owing to the deep-
layer westerly flow on the south side of the upper low. Under
the assumption that storm organization is limited today and a
west-east band of convection doesn't develop (a setup for
training), the risk for flash flooding should be much more
limited/localized than what we saw yesterday and this past
.SHORT TERM /9 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
For tonight, the low pressure aloft and at surface continue
moving NE into New England. Their departure will allow drier air
at mid and upper levels to move in from the west overnight.
Some showers or isolated t-storms may linger into the evening
but should be gone by midnight. The air mass at the surface will
remain rather moist with little if any temperature advection.
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
The mid level low that has been impacting our weather should be
an open wave on Wednesday morning. Its axis is expected to
extend southward from Maine to the waters off the Middle
Atlantic coast at that time. The trough is forecast to continue
moving eastward and it should allow some ridging to build
overhead from the west for Wednesday and Thursday. As a result,
we may actually go two days without any precipitation in our
Surface low pressure is forecast to pass well to our northwest
and north on Thursday and Friday. It is expected to drag a
frontal boundary into our region on Friday night. We are
anticipating an increasing potential for showers and
thunderstorms on Friday and they should linger into Friday
The front may stall across our region over the weekend. The
guidance is not in very good agreement regarding the details of
any surface waves moving along the boundary. We will carry a
chance of showers and thunderstorms, mainly from Saturday night
The boundary may get a push southward early in the new week as
a mid level trough passes overhead and moves out over the ocean.
We will not forecast any precipitation for Monday.
Temperatures are expected to be seasonably warm for the period
from Wednesday through Monday. Highs should favor the middle 80s
to the lower 90s on Wednesday, Thursday and Friday, and they
are expected to be mostly in the 80s on Saturday, Sunday and
Monday. Overnight lows are anticipated to start in the middle
60s to lower 70s range during the middle and end of the week,
falling back mainly into the 60s over the weekend.
.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Late this morning through this evening...Stratus has resulted
in MVFR/IFR CIGs this morning but improvement has been observed
during the mid morning as CIGs lift. A general improvement to
VFR is expected for all TAF sites by early this afternoon.
Isolated showers already developing in vicinity of RDG and ABE
mid morning. A 2-4 hr VCTS group was including in the 12Z TAF.
The timing of VCTS (mid to late aftn for RDG/ABE and late aftn
to early eve for the other terminals) was based on when a
loosely organized convective line is most likely to develop and
move eastward later today. However, there is a potential for
isolated storms a few hours earlier and later than indicated in
the prevailing VCTS group. Brief/localized restrictions with
storms possible. Winds generally out of the W (varying from W-SW
to W-NW) 5-10 kt with gusts to 15 kt this afternoon.
Tonight...Skies should clear overnight. Winds will continue W
to NW at 5 to 10 kt.
Early Wednesday morning...Some visibility restrictions are
possible in fog and haze. West wind less than 10 knots.
Late Wednesday morning and Wednesday afternoon...Mainly VFR.
Northwest to west wind less than 10 knots.
Wednesday night and Thursday...Mainly VFR. Late night and early
morning visibility restrictions are possible. West to southwest
wind less than 10 knots.
Thursday night and early Friday morning...Mainly VFR. Late
night and early morning visibility restrictions are possible.
Light and variable wind.
Late Friday morning into Friday night...Mainly VFR with
conditions lowering in scattered showers and thunderstorms.
Southwest wind 5 to 10 knots becoming west at night.
Saturday...Mainly VFR. West to northwest wind less than 10
Sub-SCA conditions are expected to continue through today and
tonight. SW winds today will become W tonight with the passage
of a surface trof. Winds could gust up to around 20 kt this
afternoon and evening. Waves will be generally in the 2 to 3
foot range. A few t- storms this afternoon or evening may cause
locally higher winds and waves.
Wednesday through Saturday...No marine headlines are
A low risk for the development of dangerous rip currents is
expected for today.
The wind is forecast to be from the west on Wednesday morning
around 5 to 10 MPH. Local effects may impact the wind direction
in the afternoon but speeds will likely remain in the 5 to 10
MPH range. Wave heights should be 2 to 3 feet on the waters off
New Jersey and Delaware with a medium period swell. As a result,
we are anticipating a low risk for the development of dangerous
rip currents on Wednesday.
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