Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 150807

Area Forecast Discussion
National Weather Service Mount Holly NJ
407 AM EDT Wed Aug 15 2018

A surface trough will remain in place across the east coast
through Friday, while a back door cold front approaches the area
Thursday into Thursday night. A cold front will move across the
east coast on Saturday and stalls to our south Sunday into
Monday as high pressure builds across New England. This front
will return north as a warm front Tuesday into Tuesday night,
before another cold front moves across the area Wednesday.


A mid level trough extended from New England to the waters off
New Jersey and Delaware early this morning. The feature will
continue to progress eastward today, allowing some ridging to
build overhead from the west.

A westerly surface flow should result in decreasing humidity
levels for today, although temperatures will become rather warm.
Highs are forecast to be around 90 degrees in much of our
region, with readings not getting above the 80s at the shore and
in the elevated terrain of the Poconos and far northern New

Most of the latest guidance has been backing down on the
minimal possibility of scattered showers and isolated
thunderstorms in our northwestern counties for this afternoon.
The NAM Nest remains a bit aggressive with the idea. However, we
have decreased the chances of precipitation in our forecast due
to the presence of the mid level ridge.


The mid level ridge should continue to influence our weather
for tonight with weak surface high pressure nudging into our
region from the west.

The wind should become light and variable for tonight with lows
ranging from the middle 60s to the lower 70s. We have included
patchy fog after midnight.


An active weather pattern will continue for the end of this
week, through the weekend and into early next week, although it
will not rain the entire time.

On Thursday, a surface trough will be in place across the east
coast, while a back door front approaches the area from the
north later Thursday into Thursday night. The back door front is
not expected to fully make it into our area. This will allow
for thicknesses and 925mb temperatures to remain elevated across
the area. Temperatures are expected to remain well above normal
across the area. Dewpoints are low enough that heat index
values are expected to remain below advisory levels. There will
be a slight chance of showers and thunderstorms during the day
and overnight Thursday as several short wave/vorticity impulses
will move across the area and create isolated to scattered
showers and thunderstorms.

The surface trough remains in place through Friday, and the
warm temperatures continue as well. Dewpoints may increase some
as the southwesterly flow increases, so heat index values on
Friday may approach advisory levels for some areas, mainly along
the I-95 urban corridor. Shower/thunderstorm chances increase
on Friday as a stronger short wave/vorticity impulse moves
across the area. There is not much in the way of shear, but
there will be a fair amount of instability with CAPE values
1,500-2,000 j/KG. Even without strong shear, if any storms build
tall enough, some small hail and locally gusty winds will be
possible in addition to heavy rainfall. PW values increase to 2+
inches, so there will be heavy rainfall, although the storms
should have a steady enough forward motion to limit a
significant flooding threats. The showers and thunderstorms
should continue into the evening, before diminishing overnight
as daytime instability wanes and the stronger short wave passes
to our east.

On Saturday, an area of low pressure will move out of the Great
Lakes region and toward New England, pulling a cold front
across the area, then the front will slowly push to our south
overnight Saturday. There will continue to be a chance of
showers and thunderstorms Saturday into Saturday night as
additional short waves/vorticity impulses move across the area.

The front will stall to our south Sunday into Monday as high
pressure builds across New England. However, a couple of short
waves/vorticity impulses are expected to pass across the area
north of the frontal boundary Sunday, which may create some
showers or thunderstorms, especially across the southern half of
the area.

Sunday night through Monday night, the high is forecast to
build a little farther south across our area, which will allow
PW values to drop below one inch and provide dry weather.

However, this dry weather will be temporary as showers and
thunderstorms return to the forecast Tuesday and Tuesday night.
The frontal boundary to our south is forecast to lift northward
as a warm front late Tuesday into Tuesday night, before a cold
front moves across the area next Wednesday. Showers and
thunderstorm return to the forecast late Tuesday into Wednesday,
and as PW values increase, the potential for heavy rainfall


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR with scattered clouds. West wind 6 to 10 knots with
gusts of 14 to 18 knots.

Tonight...Mainly VFR with scattered clouds. Local visibility
restrictions in fog after 06Z. Light and variable wind.


Thursday-Thursday night..Generally VFR. Slight chance of
showers and thunderstorms which may temporarily lead to lower

Friday-Friday night....Generally VFR. Showers and thunderstorms
likely during the afternoon and evening which may lead to lower
conditions. Southwest winds gusting to 20-25 knots, becoming
westerly overnight with less gustiness overnight.

Saturday-Saturday night...MVFR CIGS possible across the area,
along with a chance of showers and thunderstorms which may lead
to lower conditions. Westerly winds early shifting to
northwesterly during the day, then northeast overnight. Winds
gusting 15-20 knots at times.

Sunday...MVFR CIGS possible to continue into Sunday. Slight
chance of showers and thunderstorms. Winds shift from northeast
early to east during the day.


Weak high pressure is forecast to build gradually over the
coastal waters of New Jersey and Delaware from the west during
today and tonight. Wind speeds are expected to remain generally
less than 15 knots with some gust into the upper teens.

Waves on the coastal waters off New Jersey and Delaware are
anticipated to be 2 to 3 feet. Waves on Delaware Bay should be 2
feet or less.


Thursday-Thursday night..Condition expected to remain below
advisory levels.

Friday-Friday night....Winds may approach Small Craft Advisory
levels Friday afternoon and evening as southwest flow increases
across the area. Seas may approach 5 feet as well late Friday
into Friday evening.

Saturday...Conditions expected to be below advisory levels on

Saturday night-Sunday...Winds and seas increase late Saturday
and Sunday and may approach Small Craft Advisory levels.


There is a low risk for the development of dangerous rip
currents for today. The wind should blow offshore for much of
the day. Breaking waves in the surf zone will likely be 2 feet
or less with a medium period southerly swell.





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