Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 220128
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
928 PM EDT WED SEP 21 2016

.SYNOPSIS...
High pressure will continue to build southeastward over the region
tonight and become established over our area through Friday with
the remnants of Julia well offshore. A backdoor cold front will then
move through the region on Saturday and be followed by another high
pressure system building in from the northwest early next week. By
the middle of next week, a cold frontal boundary will move toward
the region from the west.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Persistent high level cirrus clouds will continue through the
overnight hours, but generally be thinning out. Aside from the
clouds, tonight looks to be a fairly nice night. Dry air advection
is expected overnight, but so far dew points have not shown much
evidence of that. Winds have decoupled across the region, so not
sure how much more we will see. Thus, expanded the mention of
patchy fog for much of the region but still think any fog will be
be patchy and will not be dense as dew point depressions remain
generally near or above 10 F as of 9 PM EDT (would normally expect
lower dew point depressions this late to have widespread fog).

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Thursday will be similar to today but with an easterly flow, it
might end up a degree or two cooler but areas along the coast will
be closer to 5 degrees cooler today. Temperatures across the region
will generally be around 80 to 85 with mid to upper 70s along the
coast.

The remnants of Julia may keep the clouds around our southern areas
for a bit longer into Thursday but it looks like the bulk of the
showers will remain to the south and east of the area.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Thursday night through Friday night:

High pressure will continue to build into the region Thursday
night and become established across the region on Friday.
Favorable conditions for radiational cooling are expected Thursday
night with lows in the 50`s and low 60`s. Some cloudcover ahead of
an approaching frontal boundary may keep low temperatures slightly
higher Friday night. Friday looks like the last of the anomalous
early fall heat for at least a little while with temperatures well
into the 80`s. Modeled boundary layer temperatures indicators of
surface temperatures match well with MET/MAV and ECMWF statistical
guidance.

Saturday through Monday night:

A cold front will move from northeast to southwest across our
region. Our coolest airmass of the season will advect in as
another high pressure system dives southeast from Canada. Enough
lift and moisture may be present for a temporary increase in cloud
cover and isolated showers on Saturday otherwise continued dry
conditions. temperatures will be much cooler for the weekend.
Some indications in ensemble guidance have a slightly delayed
frontal passage which may allow for Saturday to get into the 80`s.
However, we will stick with the mean timing of early Saturday with
the operational and ensemble guidance for the frontal passage.

Much cooler air, a first real taste of fall with lows in the 40`s
and 50`s with highs in the 60`s and 70`s. Less spread with
temperatures Sunday and Monday with the ensemble guidance.

Tuesday through Wednesday:

The backdoor frontal boundary coupled with a mid-level ridge to our
west look to setup an omega block which will likely slow the
approach of the next cold frontal boundary or weaken as it moves
east. As is usually the case in the 5-7 day time period uncertainty
is present on the exact timing of this feature.

The UKMET, CMC and some ensemble data weaken the front before it
approaches our area. On the other spectrum, the GFS and GEFS are
much faster bringing it through around Tuesday. Given this spread
and questions if the front makes it to our area, will keep a dry
forecast. Low and high temperatures should slightly warm each day
unless the high pressure system sets-up just to our north. In that
case an easterly flow could slow the approach of a warmer airmass
expected ahead of the next front.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR conditions expected. Patchy MVFR fog is possible
after 06Z but with a drying airmass it seems unlikely to occur.
Winds will be light and variable for most of tonight, but should
eventually settle out of the ENE by sunrise.

Thursday...VFR conditions expected. Any early morning fog should
dissipate fairly quickly. Northeast to east winds around 10 knots or
less are expected with a slight shift towards the southeast late.

OUTLOOK...

Thursday night through Friday night: VFR.Varibale winds becoming
west-southwest but staying under 10 knots.

Saturday through Monday: VFR. An isolated shower possibile on
Saturday. Northerly winds around 10 knots Saturday afternoon with
gusts up to 20 knots then staying under 10 knots Sunday and Monday.

&&

.MARINE...
A Small Craft Advisory is in effect from 14z Thursday through
18Z Friday.

Tonight...Sub-advisory conditions are expected to continue on the
area waters tonight. Seas may near 4 feet by late tonight.
Winds will remain around 15 to 20 knot through early evening
before starting to subside a bit overnight.

Thursday...An east to northeast wind will increase through Thursday
afternoon with gusts around 20 knots. However, seas will build
in the easterly flow and are expected to exceed 5 feet along the
Delaware and southern New Jersey coast around late morning and
continue into Thursday night. As a result, we have issued a Small
Craft Advisory.

OUTLOOK...

Waveheights will start in the four to five feet range and should
slowly decrease on Friday. GWES guidance indicates a fairly high
confidence for seas to reach five feet Thursday night and early
Friday. So have issued an SCA which goes through 18z Friday. This
ending time may be slightly long but allows for wiggle room if
waveheights respond slower, typical of easterly flow. For the
weekend into early next week seas and winds are expected to remain
below SCA criteria.

RIP CURRENTS...

There is a moderate risk for the formation of dangerous rip
currents along the NJ shore and Delaware Beaches on Thursday.
Onshore flow will continue, wave heights of 3 to 5 feet are
expected, and the dominant period will either be 7-8 seconds if
the wind wave becomes more dominant (in which case wave heights
should be on the higher end of the 3-5` range) or 11-12 seconds if
the swell remains dominant (as it is Wednesday evening).

Friday...A generally low or low enhanced risk is forecast.

Weekend...There is a pretty good chance of a moderate risk for the
formation of dangerous rip currents on at least one of the weekend
days as a 4 to 5 foot ESE swell from Tropical Cyclone Karl arrives
along with a gusty northeast wind.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 10 AM Thursday to 2 PM EDT Friday
     for ANZ452>455.

&&

$$
Synopsis...Gorse
Near Term...Johnson/Meola
Short Term...Meola
Long Term...Gaines
Aviation...Gaines/Johnson/Meola
Marine...Gaines/Johnson/Meola



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