Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Remove Highlighting --
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FXUS61 KPHI 260155
Area Forecast Discussion
National Weather Service Mount Holly NJ
955 PM EDT THU AUG 25 2016
A weak cold front moves across the region on Friday, and then
remains nearly stationary just south of the region through the
weekend. High pressure builds to the north this weekend and then
moves off the New England Coast on Monday. Another high settles
over the area into the middle of the new week, but a series of
weak disturbances will pass through the region during this time.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
A cold front was located over the Great Lakes and Midwest regions
this evening. A line of showers and storms along the front was
moving into western PA/NY. The front and associated convective
activity will continue its progression downstream and should be on
our western doorstep shortly after midnight. This activity is
expected to weaken as it travels into an increasingly stable
environment farther east.
Convection should be disorganized and weak by the time it reaches
our far western zones in eastern PA (e.g., Berks, Carbon, Monroe
Counties) by around 2 AM but there is a brief window for an isolated
thunderstorm. Cannot rule out a few leftover showers or sprinkles to
be maintained farther downstream into the Delaware Valley and NJ
coast by early morning. Hires CAM guidance generally supportive of
Boundary layer decoupling has already taken place west of the I-95
as noted by calm winds. These areas (specifically the river valleys)
would be favored for the development of radiational fog tonight.
However, debris clouds from the upstream convection is expected to
move in overnight, limiting our fog threat in these inland areas.
Farther east toward I-95 and the coastal plain, a S-SW winds around
5-10 mph will likely continue overnight in many places. This will
also hinder the setup for fog overnight.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
Latest models trended faster with the weak cold front. GFS is the
most progressive, showing the cold front arriving at the I95
corridor by 15Z. Given the upper level ridge and strength of the
low level southwesterly flow ahead of the front, this appears to
be too fast. Still, did speed up the timing slightly (closer to
the NAM), with the front now arriving at the I-95 corridor near
18Z. Given the faster arrival of the front, expect heat index
values to fall short of heat advisory conditions (though we
may not see significant cold air advection just behind the front,
expect there will be some dry air advection through the day). The
heat index is forecast to be between 100-105F range in southern
DE and adjacent eastern MD, which is awfully close to heat
We do not expect much in the way of precipitation with an absence
of organized lift and with a convective lid being provided by a
strong mid-level subsidence inversion on the northern periphery
of the upper ridge. An isolated shower is possible near the coast
during peak heating but deeper convection needed for thunderstorm
development is not favored in this environment.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Cold front continues to push south of the region Friday night.
Behind that front, high pressure builds into the Great Lakes
region and will slowly track east through the weekend. Northerly
flow ahead of the high will usher a much dryer airmass into the
region on Saturday with surface dewpoints falling from the upper
60s to near 70 Friday evening to the upper 50s to around 60 by
Saturday afternoon. High temps will only be a few degrees cooler
compared to Friday, but conditions will feel more comfortable due
to the lower humidity levels.
The center of the high will pass over central NY/PA Saturday
night, and then moves off the New England Coast on Sunday. Return
flow sets up behind the departing high, and returns flow sets up
with surface dewpoints creeping back up into the mid and upper
60s, making it a bit more humid compared to Saturday.
Cold front then approaches on Monday and slowly passes through
the region on Tuesday. Isolated showers and thunderstorms are
possible Monday afternoon and evening, and then there is a better
chance for showers and thunderstorms on Tuesday with the passage
of the front. There currently is not much upper level support, so
will keep POPs capped at low end chance for now. Thereafter,
surface high pressure settles over the Great lakes and Ohio Valley
into the middle of the week. However, a series of weak upper level
shortwaves and vort maxes will pass through the region, touching
off isolated to scattered showers and thunderstorms during that
time. Will go no higher than low chance for POPs.
Temperatures will continue to run several degrees above normal
through the middle of next week, but should as hot as Friday.
.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Mainly VFR conditions tonight. There may be an isolated shower in
our western terminals between 06-08Z. Patchy fog is possible but
the setup does not look as favorable for as it did before with
convective debris clouds moving in late tonight.
Winds shift from SW to W and then NW during the morning behind a
cold front. There is a small chance (too small to mention in the
TAFS at this time) that MVFR ceilings could develop in wake of the
fropa Friday morning.
Friday night through Sunday night...VFR. Light N winds will
become NE on Saturday afternoon, and then will become SE on
Monday through Tuesday...Mainly VFR. Isolated to scattered
showers and thunderstorms possible.
Gusts at or above 20 kt will continue through the overnight
hours, but are expected to stay below SCA criteria at this time.
By tomorrow, winds should begin to decrease.
Friday night through Tuesday...High pressure passes well north of
the waters this weekend. A cold front approaches on Monday and
slowly passes across the waters through Tuesday. Sub-Small Craft
Advisory conditions expected to continue across the waters.
For today...The risk for the formation of dangerous rip currents
is low for the New Jersey shore and the Delaware beaches tomorrow.
However, if winds remain backed more out of the south than what we
are currently forecasting, then a moderate risk could develop at
our NJ beaches.
The probable risk for the formation of dangerous rip currents
on Saturday appears to be low at this time.
Sunday through Wednesday...model ensemble guidance on every
successive cycle continues to send 2-4 ft long period (15 to 17
second) east southeast swell into our waters from the central
Atlantic - Gaston. It could be even higher but we`re taking the
conservative approach at this time from this distant offshore
hurricane. This is all dependent on size, strength and track but
there is little doubt that swells will build here...just how much
is the question. Swimming and wading dangers will probably
increase. For now we`re anticipating a moderate or greater risk
for Monday through Wednesday and possibly starting Sunday.