Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 211603
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1203 PM EDT Sun May 21 2017

.SYNOPSIS...
High pressure from eastern Canada to New England will move offshore
this afternoon. A cold front will move east into Mid-Atlantic states
later Monday then stall just off the New Jersey and Delaware
coasts Tuesday while weak high pressure spreads to our north.
Low pressure will pass east of New Jersey early Wednesday. A
cold front will cross our area Thursday, followed by a secondary
cold frontal passage on Friday. High pressure will build across
the southeastern United States, and ridge up into our area over
the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
1201PM ZFP AFM PFM GRIDS update: Have slowed down the rain
onset and this is the probable 330 PM fcst for rainfall tonight
and Monday.


1040AM ESTF AFM/PFM/FWF updates for lower RH this afternoon and
adjust skycover.

930 AM ESTF: raised temps inland a few degrees and lowered dewpoints
with some adjusted wind speeds skycover due to reality and 12z hrrr
blended with prior guidance.

Lots of cloudiness today DE/MD e shore northward into e PA
while NJ appears to enjoy the nicest weather. East to southeast
wind gusting 15-20 mph this afternoon.

Tonight...models have been differing on the timing of rain onset
tonight with the NSSL WRF and NAM significantly slower than the
GEFS/NCAR ensembles. Thinking we will slow down the onset but
go 100 PCT rain E PA around 09z/22. 09z/21 SREF modeled PWAT
increases to 1.7" by morning Delmarva.

Rain is expected to begin to move into the area close to midnight
as the mid level vorticity max and the warm front get closer to
the region. Localized flooding in poor drainage areas is
possible toward dawn across the DELMARVA.

As for thunderstorms, some model soundings show very meager elevated
instability through the later half of the night, primarily across
Delmarva. Therefore, stayed close to the previous forecast with a
slight chance of thunderstorms across Delmarva 08Z and later.
Otherwise, expect showers across the region through the overnight
hours.

&&

.SHORT TERM /MONDAY/...
Monday...A wet day is in store for the region as a cold front
approaches and moves through our area. Elevated instability
looks good enough to maintain thunderstorms and we continue to
mention this in the forecast throughout the day. Rain will be
heavy at times, especially in convection se of I95. as PWAT
values remain near 1.7 inches through Monday with this possibly
leading to some poor drainage flooding. The 12z/21 NAM is
correctly in my opinion focusing heaviest rain near a weak warm
frontal sfc low across s NJ and the DELMARVA which can more
easily accommodate 2 inches of rain in 6 hours Monday morning.
Am expecting that nuisance poor drainage flood statements that
impact travel will need to be issued between 10z and 20z se of
I95. Isolated thunder may occur?

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Monday night...Rain will end from west to east. The air doesn`t
really get the chance to dry out behind the cold front and as a
result there may some fog that forms late Monday night.

Tuesday...This should be a fairly quiet day this week as we are
somewhat in between systems. Expect much of the area to remain
dry but there will remain a chance for some showers over
Delmarva and southern New Jersey.

Tuesday night through Thursday...There remains uncertainty with
the respect to a potential coastal low developing during this
week and the state of the deepening mid-level trough. The GFS is
much more robust with these features developing and
strengthening as it moves eastward and into the Mid-Atlantic.
The ECMWF has a hint of a surface low developing but does not
have the same organization as seen in the GFS and the mid-level
trough appears to progress to the east slower. Impacts across
our area, will vary based on just how strong this potential
system becomes. One thing both of the aforementioned models
agree on is that we will see more rain on Wednesday with some
thunderstorms possible later Wednesday into Thursday.

Friday through Saturday...Some showers possible Friday but a
general clearing trend is expected as we head into the weekend.
Warming is noted at 850mb and we should rise to near normal
temps on Friday and then to above normal temps by Saturday.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Today...VFR with CIGS aoa 4000 ft developing enewd. e-se wind
may gust 15-20 kt this afternoon. Pls see TAFS for details.

Tonight...VFR CIGS to start. By 06Z, expect rain showers to be
moving into much of the region. With these rain showers, expect
conditions to first lower to MVFR, and then IFR by 10z Monday.
There is a slight chance of thunderstorms very late tonight, but
it is too unlikely to include in the TAFs at this time.
southeast wind.

Monday...MVFR/IFR conditions expected in rain, heavy at times.
Slight chance of thunderstorms vcnty KMIV. southeast to south
wind.

OUTLOOK...

Monday night...MVFR/IFR conditions. Rain will end from west to
east late Monday night. Fog possible Monday night. South to
southwest will become north to northwest late.

Tuesday and Tuesday night...mainly VFR conditions expected.
North wind early will become more easterly through the day.

Wednesday...VFR conditions expected early. MVFR/IFR conditions
possible in showers. Thunder possible late. Light east to
southeast winds.

Thursday...VFR conditions expected with periods of MVFR/IFR in
showers/thunderstorms. South to southwest winds.

&&

.MARINE...
No change in the hazard grid at this time. SE wind may gust near
25 kt late this afternoon off DE.

Monday...Winds may near 25 knots on the ocean with seas nearing
5 feet later in the day. A SCA may be needed.

OUTLOOK...

Tuesday through Thursday...Both winds and waves are expected to
stay below SCA criteria.


Rip Currents:

Onshore wind and continuing easterly swell argues for a moderate
risk for the formation of dangerous rip currents.

Water temps this Sunday morning were highly variable along the
coast...upper 50s to mid 60s.

Todays safety message: during this pre Memorial Day weekend...
if you`re a weak swimmer, swim with a strong swimmer and a
flotation device nearby. Do not swim near piers and jetties
where any rip currents tend to be stronger. Respect the power of
water, and do not overestimate your swimming ability. Ocean
surf swimming is quite different than swimming in the pool or
lake. When departing the surf zone...be aware of incoming waves.
Sometimes a much larger than expected wave can knock down a
surf zone swimmer/walker, especially if your back is turned
away from the ocean. The wave knock down-face plant can cause
disabling upper extremity injury.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ454-
     455.

&&

$$
Synopsis...Meola
Near Term...Drag/Johnson 1202
Short Term...Drag/Johnson
Long Term...Meola
Aviation...Drag/Johnson/Meola
Marine...Drag/Johnson/Meola


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