Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 280136
Area Forecast Discussion
National Weather Service Mount Holly NJ
936 PM EDT Tue Sep 27 2016
A frontal boundary will stall offshore through Wednesday. Low
pressure systems over the Great Lakes and Southeast United States are
expected to drift toward the region for the later half of the
week, before finally lifting into New England for the weekend.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
An upper air analysis showed a strong closed low centered in the
Upper Great Lakes region. There are numerous short waves rotating
around this closed low, however they are west of our area.
Meanwhile, a frontal zone is stalling to our south and east.
For tonight, our region remains generally between the above systems.
There has been decent drying across much of the area today in the
wake of the aforementioned front. The main push of the drying has
slowed though toward the coast as dew points are higher compared to
farther inland. In addition some clouds lingering closer to the
coast, although satellite trends are showing more breaks occurring.
We will maintain some clouds for these areas, although at least some
clearing should occur for a time overnight. The bulk of the showers
have moved farther offshore, and the rest of the night may not
feature much of any showers from near the coast and across the
marine area. As a result, we generally went with a dry forecast.
A mainly clear sky for many areas combined with light winds will
allow temperatures to radiate decently, especially across the
northern and western areas where dew points have been much lower. It
is these locations where patchy fog may develop toward morning, and
therefore we included a mention for low-lying areas (river valley`s)
for now. Not anticipating dense fog, but there may be a few spots
where the fog reduces the visibility to less than a mile.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
The closed upper low will become entrenched over the southern Great
Lakes on Wednesday. As it does, surface low pressure will develop
along that stalled frontal boundary over the TN/OH Valleys during
the day Wednesday, and will begin to slide along the boundary to the
north and east.
Both the GFS and the NAM are in decent agreement in holding off
precip for the area until late in the day. Most of the day Wednesday
should be mainly dry for most areas, but with a developing onshore
flow, and increasing low level moisture, can expect lower clouds to
develop starting in the late morning. Cannot rule out some patchy
drizzle during the day, but areas most impacted by any showers will
be southern areas, and then the showers slowly work their way up to
the north late in the day. As of now, PoPs were kept on the low
side, however did raise them to likely late in the afternoon across
the far south.
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
An unsettled period is in store for the first part of the extendd
High pres will remain over ern Canada and New Eng, with a large
upr low spinning around to our sw. One area of low pres, moves by
to the w Wed night into erly Thu. THis feature has the potential
to bring the heaviest, steadiest rain to the area durg this pd.
However, guid continues to suggest that the highest qpf will be to
As is often the case with upr lows, there will be an abundance of
clouds and periods of rain, but determining when and where it will
rain is difficult and the mdls are disagreeing.
Durg the day Thu, there cud be a break, especially over nrn areas.
Mdls diverge considerably Thu night into erly Fri with the GFS
remaining drier and the ECMWF and NAM wetter.
Later Fri into Fri night could see another lull.
Over the weekend, the upr low begins to fill and lift out and
precip chcs will gradually decrease. However, there will at least
be some chc on Sat, especially n and psbly into Sun before all
rain chcs come to an end erly next week.
Temps look to be around nrml. QPF values could reach 2 to psbly 3
inches on the lwr Delmarva and less elsewhere.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Overnight...VFR overall, although a ceiling will linger for
awhile longer at or near MIV and ACY. Local fog toward morning may
result in MVFR/IFR visibility for a time, however confidence is
not all that high for most areas therefore just included light fog
at MIV for now. Light south-southwest winds, becoming light and
variable to calm at most terminals.
Wednesday...VFR ceilings developing in the morning, then lowering to
MVFR from southeast to northwest during the course of the day. An
onshore flow is expected to increase, therefore lowering ceilings
may occur fairly quickly. A few showers are possible especially in
the afternoon, with even some drizzle possibly developing for some
areas. East-northeast winds 3-6 knots to start, then increasing to
10-15 knots in the afternoon.
Wed night thru Thu...MVFR/IFR conds likely with SHRA, some psbly
hvy. Mdt confidence. ENE wind around 20 to 25 kts on Thu for KACY
and psbly KMIV.
Thu night thru Fri...Some improvement is psbl, but MVFR is likely
with lower conds in any SHRA. ENE wind 20 to 25 kts for KACY. Low
to mdt confidence.
Sat thru Sun...Mainly VFR, but some lower conds psbl in sct
shwrs. Mdt Confidence.
Light winds this evening, becoming NE 5-15 KT after midnight. Seas
will remain mostly 2-4 FT.
On Wednesday, winds and seas will begin to ramp up as low pressure
approaches from the south and west. Small Craft Advisory conditions
with winds gusting to 25 KT and seas building to 5 FT will develop
over northern ocean waters Wednesday afternoon, so a SCA has been
issued for those waters for Wednesday afternoon.
A gale watch for the northern coastal waters and SCA elsewhere
has been issued for Wed night thru Thu for increasing ENE wind and
seas. Confidence was not high enough to extend gale watch further
s. A prolonged sca will likely be needed into at least Saturday.
Seas will build into Fri and could reach 9 to 10 feet before
There is a moderate risk for the formation of dangerous rip
currents Wednesday. This is due to the combination of an
increasing onshore wind and building seas.
Spotty minor tidal flooding on the oceanfront is possibile with
the Thursday and Friday high tidal cycles.
MARINE...Small Craft Advisory from 6 PM Wednesday to 8 PM EDT Thursday
Gale Watch from Wednesday evening through Thursday evening for
Small Craft Advisory from 1 PM to 6 PM EDT Wednesday for