Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 212246

Area Forecast Discussion
National Weather Service Mount Holly NJ
646 PM EDT Sat Oct 21 2017

High pressure will shift offshore on Sunday and Monday. A strong
cold front is forecast to move across our region Tuesday night. Low
pressure is expected to develop along the front and it should be
located over or near New England and southeastern Canada on
Wednesday and Thursday. High pressure is anticipated to follow for
Friday and Saturday.


An upper air analysis early this evening shows a ridge axis near the
East Coast. A 250 mb jet is positioned from the Southern Plains to
the Midwest with a second segment from the Mid-Mississippi Valley to
north of the Great Lakes. At the surface, high pressure is centered
near the Delmarva coast.

High pressure at the surface will slowly move offshore through the
overnight. Satellite imagery shows quite a bit of cirrus streaming
northward all the way from the Gulf Coast states this evening, and
this is expected to continue through the overnight although it may
thin at times. The sky cover was adjusted upward a bit. The presence
of the cirrus, especially if it is thick enough, should limit fog
development late tonight despite the dew points rebounding. Given
the light to calm winds at the surface though, we did keep some
patchy fog especially for parts of northeastern Pennsylvania and
northwestern New Jersey.

The temperatures are dropping fairly quickly already this evening in
the outlying areas , however not quite as fast as last evening due
to the presence of the cirrus plus higher surface dew points. The
cirrus should temper the radiational cooling to some extent.
Overall, no major changes were made to the low temperatures. For the
latest update the hourly temperature, dew point and wind grids were
adjusted based on the latest observations, then the LAMP guidance
was blended in for a little while to assist with trends.


Winds will still be light but start to come from the southeast
on the backside of the high. This will lead to a further
increase of moisture and warm air into the region. The overall
moisture transport looks slow, so we should be able to get one
more mostly sunny day tomorrow. Temperatures will warm fairly
rapidly as well into the mid and upper 70`s, perhaps a degree or
two cooler than today based on modeled 925 mb temperatures.


The surface high will be well off the coast on Sunday night and
Monday. The return flow on the back side of the high is
expected to bring increasing moisture into our region. As a
result, we continue to anticipate low clouds and patchy fog for
late Sunday night into Monday morning.

The axis of the mid level ridge is forecast to be located along
the east coast on Sunday evening. A mid level low is expected
to be centered over Missouri at that time. As the ridge moves
out to sea, a re-enforcing long wave trough should begin to drop
over the Mississippi River Valley. The mid level low is
anticipated to fill with its remnants being drawn up and over
our region late on Monday night. The long wave trough is
forecast to influence the eastern states during the mid week
period before it lifts to the northeast.

The surface cold front is expected to extend from the Great
Lakes to the central Gulf Coast on Sunday night. The feature
should already be tapping into gulf moisture at that time. As
the remnants of the mid level low pass overhead and as the cold
front approaches, there will be an increasing chance of showers
in our region from Monday night into Tuesday. Enhanced lift from
late Monday night into Tuesday will likely result in period of
moderate to heavy rain along with a chance of thunder. It
appears as though rainfall totals will favor the 0.25 to 1.00
inch range.

The cyclonic flow aloft along with the slowly departing cold
front and surface low pressure over or near New England should
keep clouds and a low or slight chance of showers in our region
during the mid week period.

High pressure is expected to bring some clearing for Friday and

Daytime temperatures will remain about 10 degrees above normal
on Monday and Tuesday. Readings are forecast to drop back to
more typical levels for late October during the period from
Wednesday through Saturday.


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

Tonight...VFR with clouds around 25000 feet. Light and variable to
calm winds.

Sunday...VFR. Light and variable to calm winds, becoming
southeasterly less than 10 knots. Some low clouds however may start
to approach KACY and KMIV after 21z, however this is very low
confidence at this time.

Sunday night and Monday...Low clouds and fog are possible mainly
late Sunday night into Monday morning. Otherwise...mainly VFR.

Monday night through Tuesday night...Conditions lowering to
MVFR and IFR in showers. Isolated thunderstorms and moderate to
heavy rain are possible on Tuesday, along with a south wind
gusting around 25 or 30 knots.

Wednesday...Conditions improving to VFR.

Wednesday night and Thursday...Mainly VFR.


Wave heights will be in a fairly stable state of around two feet
through Sunday. East to southeast winds will be under 10 knots
through Sunday.

Sunday night through Monday night...No marine headlines are

Tuesday and Tuesday evening...A Small Craft Advisory may be
need for southerly wind gusts near 30 knots. Waves on our ocean
waters may build to 7 to 10 feet.

Late Tuesday night through Thursday...A Small Craft Advisory
may be needed on our ocean waters for wave heights of 5 to 6
feet, even as the wind becomes west to northwest around 10 to 20


44091 buoy drifted away from its mooring and has since been
recovered. Its return to service date is still unknown.




Near Term...Gorse
Short Term...Gaines
Long Term...Iovino
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