Areal Flood Advisory 71, NWS Philadelphia/Mount Holly

Area Forecast Discussion
National Weather Service Mount Holly NJ
625 PM EDT Wed Jun 5 2019

.SYNOPSIS...
High pressure continues to drift eastward over the Atlantic as low
pressure with an associated cold front moves through the Great
Lakes. The cold front is forecast to pass through our region on
Thursday, followed by high pressure for Friday into the weekend.
Broad low pressure and another cold front are expected to approach
slowly from the west early in the new week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
6:30 Update...

The forecast is generally on track. Made some adjustments to PoPs to
account for recent trends. Bulk of activity so far has been over
southern Delmarva. From a hydro perspective, this is not too
problematic as FFG values in that area are very high. In terms of
severe weather, we have seen one area of storms become borderline
severe in southern DE and into far southern NJ. Expecting most
convection from here to generally be sub-severe, however a few
stronger storms are possible with still a chance for one or two to
approach severe limits with gusty winds. Also noting some guidance
such as the HRRR shows activity filling in further north quite a bit
later tonight, so we will have to watch for this as heavy rainfall
tolerance levels drop dramatically towards the more urban parts of
the area. It does not appear that much if any of a nocturnal
inversion will develop this evening, so with dew points remaining
high and forcing becoming a little better, it is possible we could
get new convective initiation even as temperatures cool off a little
after dark. Previous discussion follows.

High pressure remains centered over the western Atlantic, and low
pressure over the Great Lakes will slowly pass to the north tonight.
This will drag a cold front towards the region this evening, but the
cold front itself will not cross through until Thursday. Out ahead
of the front, some mid-level shortwave energy will spawn a secondary
low over the southern Appalachians, and this low will pass through
Delmarva and southern New Jersey this evening.

A hot, humid, and unstable airmass is over the region, with surface
dewpoints well in the 60s throughout, and in the upper 60s to around
70 in southern New Jersey and Delmarva.

This is resulting in upwards of 2000 J/kg of MUCAPE and SBCAPE
across Delmarva and southern New Jersey, and 500-1000 J/kg across
the northern half of New Jersey and into southeast Pennsylvania.
PWATs are generally 1.5-1.7 inches in the southern portions of the
forecast area, but should climb up to around 2 inches this evening.

This sets the stage for a round of potential severe thunderstorms,
as well as locally heavy rain. Based on latest trends, the area of
heaviest rain would affect Delmarva and southeast New Jersey, where
the highest instability and highest dewpoints are. However, latest
Flash Flood Guidance values suggests it would take 2-3" of rain in 1
hour; and 3-4 inches of rain in both 3 hours and 6 hours for Flash
Flooding to occur. Since storm total QPF is generally on the order
of 1-2" (though locally higher amounts are possible), do not think
this will lead to flash flooding, so will not issue a Flash Flood
Watch. Models are also indicating a potential swath of heavy rain
just north of Philadelphia, so it is possible for some urban
flooding this evening.

Convection is possible in northern new Jersey (north of I-195), the
Lehigh Valley, and the southern Poconos, but does not look to be as
organized as the convection down south.

With loss of diurnal heating after sunset, instability drops off
fairly quickly. Heavy rain still possible, but the severe threat
drops off.

Several waves of showers and thunderstorms will affect mainly the
southern half of the forecast area through midnight or so.

Once the precip ends, it remains warm and humid into Thursday
morning. Fog and stratus likely to develop.

Lows tonight in the 60s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Surface cold front slowly works it way across the region on
Thursday. However, there does not appear to be much upper level
support with its passage. Although it remains quite warm and humid
ahead of the front, there may not be much energy with which to work
to fire off much convection. Will keep PoPs capped at slight chance
to low end chance.

Going through the day, cooler and dryer air filters into the region
behind the front, but pretty much only for the northern half of the
CWA.

Highs once again in the mid and upper 80s south and east of I-95,
and in the lower 80s north and west.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Thursday night through Sunday...

High pressure will build in to our north through Friday leading to a
continuing drying of the airmass with a sky that will generally be
mainly clear to partly cloudy. Highs Friday will mostly be in the
low 80s however an E/NE flow around the high will keep it a bit
cooler along the coast and it will also be a bit cooler over the
southern Poconos.

Surface high pressure builds S/E from Ontario/Quebec into New
England through the course of Friday night and Saturday with an
upper level ridge setting up over Ontario. These features should
continue to dominate our weather through Saturday leading to plenty
of sunshine with seasonable temperatures and comfortable humidity
levels. However we will have to keep an eye on a large upper level
low with associated tropical moisture and rainfall over the
southeastern states but at this point forecast models continue to
indicate this should stay suppressed to our south through at least
Saturday.

Saturday night through Sunday, the upper low over the SE opens up
with the upper ridge over the Great Lakes starting to slowly weaken
and shift east...becoming centered just off the coast by late
Sunday. Expect the area should still remain largely protected by the
ridge through with mainly dry weather through the weekend. That
said, latest guidance does bring the moisture over the SE a little
farther north by late Sunday so will maintain the mention of chance
POPs over the Delmarva.

Sunday night through Wednesday...

In the big picture, the weather pattern becomes more unsettled once
again next week as a large upper level trough digs S/E from Canada
towards the northeastern US and also interacts with the upper trough
and tropical moisture over the SE. Depending on exactly how these
features interact, which is currently uncertain, will determine the
more specific details of the forecast in terms of how much rain
falls and when. However expect increasing chances for showers and
thunderstorms by Monday across the area as extensive moisture is
advected northward up the coast in a deep layer southerly flow.
Still many days out but the concern is the moisture will be of
tropical origins with PWATS potentially exceeding 2 inches so any
showers/storms could be heavy.

Showery/stormy weather has a good chance of continuing Monday night
into Tuesday as a frontal zone moving in from the west associated
with the Canadian upper level trough interacts with the extensive
moisture along the east coast. Main question will be how quickly
this moves through and again this will depend, among other things,
on the interaction of the digging Canadian / northern stream upper
trough with the SE CONUS upper trough. If a wave develops along the
front near or just south of the area a more prolonged period of
heavy rainfall will be possible around Tuesday or Wednesday of next
week as opposed to if it sweeps through faster as a more progressive
cold front.

&&

.AVIATION /22Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...SHRA/TSRA with heavy rain this evening, mainly south and
east of KPHL. Conditions down to IFR, possibly lower, in TSRA, which
could last through around 05Z. Fog/stratus developing thereafter,
with conditions falling to IFR or lower.

SW winds around 10 kt, possibly gusting to 20 kt, diminishing to 5
kt or less tonight.

Thursday...Morning fog/stratus gives way to VFR conditions.
Scattered SHRA/TSRA in the afternoon, but confidence is low. West
winds 10 kt or less, becoming NW in the afternoon.

OUTLOOK...

Thursday night...Mainly VFR. Northwest to north wind 5 to 10 knots
becoming NE late at night.

Friday...VFR. Northeast to east wind around 10 knots.

Friday night...Mainly VFR. Northeast to east wind 5 to 10 knots or
less.

Saturday...VFR. East to southeast wind around 10 knots.

Saturday night...Mainly VFR. Northeast to east wind 5 to 10 knots.

Sunday...Mainly VFR. East wind around 10 knots.

Sunday night through Monday...Increasing clouds with showers and
storms possible by Monday along with associated restrictions. SE
winds 5-10 knots.

&&

.MARINE...
SCA in effect for the coastal ocean waters for tonight and into
Thursday afternoon, as southerly winds range from 15-20 kt with 25-
30 kt gusts. Showers and thunderstorms will pass through the waters
tonight, with thunderstorm wind gusts in excess of 34 kt possible,
as well as torrential rainfall.

Winds shift to the W-SW at 10-15 kt late Thursday, and seas subside
to 3-4 feet.

OUTLOOK...

Thursday night through Monday...Wave heights could reach near 5 feet
Saturday night into Sunday as E/NE winds increase with gusts to near
or just over 20 knots. Otherwise, no marine headlines expected.

RIP CURRENTS...

There is a moderate risk for the development of dangerous and life
threatening rip currents through tonight at the New Jersey and
Delaware beaches due to the strong southerly flow.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 1 PM EDT Thursday for ANZ450>455.

&&

Synopsis...Fitzsimmons
Near Term...MPS/O'Brien
Short Term...MPS
Long Term...Fitzsimmons
Aviation...Fitzsimmons/MPS
Marine...Fitzsimmons/MPS

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
625 PM EDT WED JUN 5 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0600 PM     MARINE TSTM WIND STONE HARBOR            39.06N 74.77W
06/05/2019  M46 MPH          ANZ453             NJ   MESONET

            HADS SENSOR.

&&

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Special Weather Statement
National Weather Service Mount Holly NJ
658 PM EDT Wed Jun 5 2019

NJZ018-019-PAZ071-052330-
Northwestern Burlington-Camden-Philadelphia-
658 PM EDT Wed Jun 5 2019

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT NORTHWESTERN CAMDEN...
NORTHWESTERN BURLINGTON AND CENTRAL PHILADELPHIA COUNTIES...

At 657 PM EDT, radar indicated strong thunderstorms were located
along a line extending from near Riverside to Ramblewood. Other
storms were developing near the Walt Whitman Bridge. Movement was
northeast at 35 mph.

Wind gusts up to 40 mph are possible with these storms.

Locations impacted include...
Philadelphia, Camden, Gloucester City, Cherry Hill, Mount Laurel,
Willingboro, Lumberton, Florence, Bellmawr, Burlington, Bristol,
Mount Holly, Riverside, Palmyra, Westville, Bordentown, Beverly,
Brooklawn, Tullytown and Pemberton.

Torrential rainfall is also occurring with these storms, and may
cause localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 3996 7461 3987 7512 3989 7514 3988 7517
      3995 7516 4007 7493 4008 7487 4013 7482
      4012 7478 4014 7474 4016 7471 4019 7470
      4017 7466
TIME...MOT...LOC 2257Z 242DEG 32KT 4002 7499 3994 7497

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Special Weather Statement
National Weather Service Mount Holly NJ
718 PM EDT Wed Jun 5 2019

NJZ013-019-020-052345-
Northwestern Burlington-Ocean-Western Monmouth-
718 PM EDT Wed Jun 5 2019

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN OCEAN...
NORTHEASTERN BURLINGTON AND SOUTHWESTERN MONMOUTH COUNTIES...

At 717 PM EDT, a strong thunderstorm was located over Jobstown, or 14
miles south of Trenton, moving northeast at 15 mph.

Wind gusts up to 50 mph are possible with this storm.

Locations impacted include...
Allentown, Pemberton, Wrightstown, Jobstown, Columbus, Woodruff,
Georgetown, Browns Mills, New Egypt, Fort Dix, McGuire AFB and
Pemberton Heights.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 4001 7441 3996 7471 4004 7476 4015 7463
      4014 7462 4014 7459 4017 7461 4018 7460
      4018 7458
TIME...MOT...LOC 2317Z 225DEG 12KT 4002 7470

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