Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 291934
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
334 PM EDT Sat Apr 29 2017

.SYNOPSIS...
A weak cold front will cross the area tonight before dissipating
south of the region Sunday. A ridge of high pressure will be across
the area Sunday before low pressure and its associated fronts move
towards the Middle Atlantic later Monday and Monday night. High
pressure will build in for the middle of next week. Another low will
affect our area towards the end of next week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Near record to record warmth occurring in some places this afternoon.

An upper-level ridge, centered just off the coast of the Carolinas,
is forecast to build slightly to the north over our area tonight.
This is in response to a potent closed low across the Central and
Southern Plains. Meanwhile, a surface cold front (located just to
our northwest at mid-afternoon) will settle south-southeastward
across our area tonight with high pressure building across portions
of eastern Canada. A notable airmass change will occur through
tonight behind the cold front and courtesy of the aforementioned
high pressure system.

For the rest of this afternoon and going through this evening, a
very warm to hot airmass is in place ahead of the cold front. The
dew points have mixed out some for several spots this afternoon,
which has eased up the humid feel a bit. An analysis shows
instability has been gradually increasing northward as the
convective debris cloudiness has thinned quite a bit allowing for
more heating of the boundary layer. There is not much in the way of
forcing though, with one notable short wave tracking across western
and central Pennsylvania northeastward. The associated convection
with this continues to weaken, although some showers may clip the
southern Poconos. There is some isolated renewed development to its
south/southwest however.

The best chance, and even this looks to be on the lower side,
appears to be across portions of Delmarva and southern New Jersey
where some high-res model guidance wants to move some convection
across early this evening. It appears that Philadelphia is on the
northern edge of this potential convection. This is less certain as
there does not appear to be much forcing for convective organization
plus the mid level ridge is building some. We will continue to place
the highest (chance) PoPs across these areas for awhile this evening
then gradually lower and shift them southward with the cold front.
Given the amount of instability across the southern zones along with
some drying aloft could result in a few storms that are able to
develop produce locally gusty winds this evening.

Otherwise, a wind shift to the north and northeast will occur
through the night as the cold front works southward. This will drive
some drier air southward as a result and the forecast soundings are
not really robust with low clouds/fog developing as a result. There
should at least be some stratocumulus development especially as the
northeast low-level flow gets going. Low temperatures are mostly a
MOS/continuity blend.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
The weather will be rather different Sunday compared to today
(Saturday) in the wake of a cold front. This front is expected to
clear our entire area before stalling in a west to east orientation.
An upper-level ridge axis should be moving across our area, allowing
surface high pressure to build to our north and east. This will
allow for a northeast low-level flow which should become east and
then southeast with time. This will allow for a much cooler airmass
to be over our area, enhanced by the flow off the colder ocean
waters.

While there may be areas of stratocumulus, the cloud bases may lower
especially in the afternoon as the flow turns more east and
southeast resulting in some increase in the moisture. Overall
though, there should be a fair amount of cloudiness across the
region during the day. As of now other than some slight chance PoPs
early across parts of Delaware and Maryland, opted to go with a dry
forecast as there is no real clear forcing with the
southward/stalling front. Any remaining instability in the southern
areas should be more elevated given the onshore low-level flow.

High temperatures were a MOS/continuity blend, then some tweaks were
made mostly along the coast.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
A weak ridge of high pressure will be across the area during the
start of the long range. It will remain in place through Monday
before moving to the east. Dry weather is expected Sunday night,
then clouds will increase Monday along with the chances for a few
showers across the N/W areas Monday afternoon. Temperatures will be
above normal with highs Monday in the low 80s over srn NJ and
Delmarva while highs will be in the mid/upper 70s across the N/W
areas.

A low pressure system across the upper Great Lakes Monday morning
will move NE across southern Canada through Wednesday. A strong cold
front will move across the Middle Atlantic Mon night and into early
Tue. There appears to be a decent chc for showers and tstms with
this front, so only small changes to the already high pops were made
today. We have categorical pops N/W and high Likely S/E. It could be
a 1/4 to 1/2 inch rain producer, higher in tstms. On Tuesday, the
front will be east of the area, but the lingering upper low aloft
will lead us to keep the chc for some showers into the early
afternoon. High temps Tue will still be a little above normal S/E
but by Wed, readings will be close to normal for early May.

A short period for far weather Wed/Wed night with an area of high
pressure across the area. Another low will approach Thu and will
again bring decent chc for showers and sct tstms (Delmarva) for the
end of next week. We have some likely pops for many areas Thu/Thu
night and chc pops for Fri/Sat. Temperatures will be near or
below normal towards the end of the week.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Rest of this afternoon...VFR with clouds at or above 5000 feet.
There is a chance for a few showers and thunderstorms to develop
after 21z mostly southwest of PHL. The coverage and timing of
showers/thunderstorms is low. A VCTS is carried for PHL, ILG, MIV
and ACY toward early evening. Winds varying between west-southwest
and west-northwest around 10 knots with local gusts to around 20
knots at times.

Tonight...A few showers or thunderstorms possible mainly in the
evening especially near and southwest through east of PHL with
locally reduced ceilings/visibilities, otherwise any ceilings should
remain VFR. Northwest winds mostly 10 knots or less, becoming north
and then northeast.

Sunday...VFR ceilings may lower to MVFR through the day, however
confidence is on the lower side. Northeast winds around 10 knots,
becoming east and southeast in the afternoon.

OUTLOOK...
Sun night thru Mon Afternoon...Mostly VFR expected.
Mon night thru Tue...Restrictions with showers especially Mon night.
Tue night thru Wed night...Mostly VFR. Patchy morning fog psbl.
Thu...Restrictions possible with showers.

&&

.MARINE...
The conditions are expected to remain below Small Craft Advisory
criteria through Sunday. A few thunderstorms this evening may
produce locally gusty winds, however coverage and timing is
uncertain. A cold front will cross the area this evening, resulting
in a wind shift to the northwest and north then to the northeast
through the night. There could be a northeast to east wind surge
Sunday especially across the northern coastal waters zones, however
held gusts below 25 knots. The duration of this does not look long
enough and therefore kept seas 4 feet or less.

OUTLOOK...
Sun night thru Mon morning...Sub-SCA conditions with Fair weather.
Mon afternoon thru Tue night...SCA expected. Showers with sct tstms.
Tue night...SCA on the ocean and sub-SCA across Del Bay. Fair.
Wed thru Thu...Sub-SCA. Fair thru Wed night then sct showers
Thu.

&&

.CLIMATE...
We have already issued a RER product for a new record high
temperature at Georgetown, DE. Atlantic City is close as of last
hour. Other products are possible this afternoon.

&&

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

&&

$$
Synopsis...O`Hara
Near Term...Gorse
Short Term...Gorse
Long Term...O`Hara
Aviation...Gorse/O`Hara
Marine...Gorse/O`Hara
Climate...O`Hara


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