Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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618
FXUS61 KPHI 240738
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
338 AM EDT Thu May 24 2018

.SYNOPSIS...
High pressure builds across our region through today before shifting
offshore Friday. A cold front moves southward across our area late
Saturday night through Sunday, then stalls in our vicinity through
Monday. Weak high pressure then moves in Tuesday before moving
offshore Wednesday.
&&


.NEAR TERM /UNTIL 6 PM THIS EVENING/...
High pressure was centered to our west across the Midwest-Great Lakes
region early this morning. The high will build into the Mid-
Atlantic states today. Farther downstream, a weak area of low
pressure was moving southward and farther away from Cape Cod.

The forecast essentially calls for a repeat of yesterday`s weather
except we`ll start the day sunny unlike yesterday`s morning
clouds. Forecast highs are generally in the low 80s. Temperatures
will be cooler but comfortable across the higher terrain in
northeast PA/northwest NJ and at the beaches with highs in the
low to mid 70s.

The winds (albeit light) across the forecast area have begun to veer
out of the northwest in response to a subtle surface trough
(extending to the west-southwest of the offshore) advancing
southward through the region. Expect the winds to veer slightly
after sunrise and remain northerly through early afternoon. A sea
breeze is expected to develop early to mid afternoon. Offshore
synoptic flow may delay formation of the sea breeze front or slow
down its movement but the flow doesn`t look to be quite strong
enough to prevent this boundary from moving inland across the NJ and
DE coastal plain by late day.
&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
High pressure will gradually build southward but continue to
influence our weather. A favorable radiational cooling setup is in
store for tonight under clear skies and light winds. Accordingly,
temperatures will drop fairly quickly this evening. Forecast lows
are in the 50s area wide. Patchy radiational fog is possible,
especially in the sheltered rural valleys.
&&


.LONG TERM /FRIDAY THROUGH WEDNESDAY/...

Friday through Saturday...

Increasingly warm and humid during this period as a SW flow
takes hold around a ridge setting up over the western Atlantic.

For Friday, high pressure continues to move off the coast but will
still maintain sunny skies over the area. Increasing SW flow will
bring in warmer air so expect highs generally reaching the low to
mid 80s. The exception will be along the coast and over the southern
Poconos where temperatures will be several degrees cooler. Dew
points will also be increasing as they rise to the 55 to 60 degree
range but this still won`t feel too oppressive. Friday night, SW flow
persists with dew points continuing to nudge upward so this will
also keep temperatures up as well with lows in the 60s.

Heading into Saturday, deep layer moisture from the surface through
the mid levels continues to increase as tropical moisture from a low
over the Gulf of Mexico is drawn north around the ridge in the
western Atlantic. There will also be some lift provided by shortwave
energy moving in from the west. These factors combined with daytime
heating will lead to some scattered showers and thunderstorms
developing by the afternoon..especially near and west of the I-95
corridor. Highs will be quite warm, generally in the middle to upper
80s, with dew points in the mid to upper 60s making it feel quite
oppressive. Once again though, coastal areas and the southern
Poconos will be cooler...generally in the low 80s.


Saturday night through Wednesday....

The forecast becomes a little more complex for the middle to latter
part of the holiday weekend into next week. At the surface, a
backdoor cold front looks to move south into the area Saturday night
into Sunday then stall. Meanwhile, tropical moisture will continue
to stream northward from the Gulf of Mexico into the Mid Atlantic
region intersecting this boundary. Lift will also be provided by PVA
as an upper level trough moves through from the Great Lakes across
the northeast Sunday into Monday. The upshot of all this is that
Sunday currently looks to be unsettled with fairly widespread
showers and thunderstorms. PWAT values will be very high...near to
even above 2 inches. So any showers and storms will be capable of
producing very heavy downpours. Will need to monitor this closely
over the next couple days as there could be hydro concerns
especially if showers/storms were to train over the same area. Still
too early though to be confident on how this will evolve though as
there may be a dry layer advecting in with the backdoor front that
could mitigate the heavy rain at least somewhat. Highs Sunday will
range from the low to mid 70s across the north (north of the front)
to the low to mid 80s across SE PA, southern NJ, and the Delmarva.
Dew points will also be in the 60s to near 70, highest south, so it
will continue to feel quite oppressive.

Showers, storms look to continue across the area Sunday night but
may tend to diminish in coverage through Monday as the
aformentioned upper level trough passes off to the east. That said,
there will still be plenty of moisture around with the front stalled
across the area so no confidence in any real drying. It will remain
humid with highs generally in the 70s to near 80, coolest north and
warmest south.

Heading toward the middle of next week, forecast confidence
decreases due to the muddled nature of the pattern. In the upper
levels, the passage of the trough off to the east looks to result in
a weak surface high trying to build in for Tuesday. However there
will still be tropical moisture trying to advance north around the
stalled low over the Gulf so this could still result in some showers
occuring across the area as the high may be quite weak, if it builds
in at all. For this reason, we keep slight chance POPs in the
forecast. The set up looks to be similar for Wednesday with plenty
of tropical moisture still streaming up through the eastern CONUS
keeping at least the slight chance of showers in the forecast for
most of the region. Highs both days look to be generally in the 70s
to around 80 with continuing fairly high humidity values.
&&


.AVIATION /08Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. NW winds 3-6 kt overnight will become more N 5-10 kt
after sunrise this morning. Winds could become light and variable
this afternoon. However, a sea-breeze front is expected to form and
move inland, passing through ACY 20-22Z and MIV 1-2 hours later. A
wind shift out of the SE will occur with sea-breeze fropa with
speeds at or below 10 kt. High forecast confidence except moderate
confidence with timing of sea-breeze front.

Tonight...VFR. The sea-breeze front may make it into the I-95
terminals, including PHL, around or shortly after 00Z. S winds 5-9
kt can be expected with fropa. Otherwise, a light S-SW wind 5 kt or
less. High forecast confidence except moderate confidence with
timing of sea-breeze front.

Outlook...

Friday...VFR. Southwest winds increase to 10-15 knots with possible
gusts up to 20 knots.

Saturday and Sunday...Mainly VFR Saturday and Saturday night with a
few showers and thunderstorms possible. Sub-VFR conditions should
occur at times Sunday with developing showers and thunderstorms
especially in the afternoon.

Monday...Sub-VFR conditions possible due to a chance of some showers
and thunderstorms.
&&


.MARINE...
Winds and seas below SCA criteria today and tonight. NW winds 8-12
kt early this morning should shift slightly out of the N later in
the morning. Light and variable winds in the coastal waters toward
midday and early afternoon when sea-breeze front starts to form. S-
SE winds 7-13 kt develops after the front moves inland late in the
afternoon and tonight.

Outlook...

Friday and Saturday...Southwesterly flow increases allowing the seas
to build some. A much warmer airmass will be moving over the cooler
waters, therefore strongest gusts may be along the coast. It is
possible that winds may gust near 25 knots at times, especially late
Friday.

Sunday and Monday...The conditions should be below Small Craft
Advisory criteria.


Rip Currents... The risk of rip currents for today is low.
Despite an onshore component to the flow with speeds 8-12 kt
this afternoon, wave heights and swells are forecast to be
around or below 2 ft.

A rip current is a small-scale surf zone current moving away from
the beach. With the upcoming Memorial Day Weekend, please keep the
following in mind:

It`s quite a bit different swimming in the ocean versus a pool. If
you`re a weak swimmer, swim with a strong swimmer and/or flotation
device nearby. Remember, a low risk of rip currents does not mean no
risk! Life threatening rip currents often still occur near jetties,
reefs, and piers. There were 8 rip-current fatalities last year
alone in New Jersey. The vast majority of Delaware/New Jersey rip
current victims swam at unguarded beaches. ALWAYS SWIM IN THE
PRESENCE OF A LIFEGUARD.

More info on identifying and surviving a rip current is available
via a post on the NWS-Mount Holly Facebook and Twitter accounts.

The latest rip current forecast is also available at
www.weather.gov/beach/phi/

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...Fitzsimmons
Near Term...Klein
Short Term...Klein
Long Term...Fitzsimmons
Aviation...Fitzsimmons/Klein
Marine...Fitzsimmons/Klein



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