786
FXUS61 KPHI 121403
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1003 AM EDT Fri Jul 12 2024

.SYNOPSIS...
Stationary front plagues the region into Saturday with several
waves of low pressure riding along it. Broad high pressure then
returns and persists through Tuesday before another cold front
approaches the area around the Wednesday-Thursday timeframe.

&&

.NEAR TERM /THROUGH TONIGHT/...
Showers and a few thunderstorms continue to spread into the
region. Some of the rain has been locally heavy, but given how
dry conditions have been, Flash Flood Guidance values are quite
high at 3 inches in 1 hour and 4.5 inches in 3 hours.

Otherwise, a stalled frontal boundary extends from Maine, runs
down the I-95 corridor along the East Coast, and into the
Florida-Georgia border. Broad low pressure lies over the
Southeast and will slowly track north on that stalled boundary
today until it lies over the Mid- Atlantic late tonight.
Meanwhile, a broad upper jet lies north of the region.

High pressure is centered about 1000 miles east of Atlantic
City, and return flow behind the high will usher abundant low
level moisture into the Northeast and Mid-Atlantic. Surface dew
points will rise into the 70s throughout the region, and
possibly to near 80 over Delmarva and along the I-95 corridor by
this afternoon. This will push PWATs up to 2 to 2.5 inches.
Surface-based CAPE values will be up around 1000 J/kg to as much
1500 J/kg. 0-6 km Bulk Shear will be minimal, generally less
than 10 kt for most of New Jersey and Delmarva, and around 15 kt
for southeast Pennsylvania. Generally speaking, a widespread
1-2" of rain can be expected, however isolated areas of 3-5" are
possible, leading to a threat of flash flooding.

While thunderstorms will be likely for most of the area, the
threat for severe weather will be low. The primary threat is
heavy rain and flash flooding. The threat comes from heavy rain
from potentially slow moving storms and storms redeveloping
throughout the day. Antecedent conditions are not conducive to
flooding (parts of New Jersey, southeast Pennsylvania, and
Delmarva are in a D0 drought, with some parts of the area in a
D1 drought), but the signals are there for flooding to develop
later today and tonight.

Showers and thunderstorms will continue to lift to the north
and west as the morning progresses, and then development
continues through the afternoon and evening.

As surface low pressure lifts north, there should be a break in
the precipitation late tonight. Given abundant low level
moisture over the area, fog will develop late tonight.

Highs today will top off in the low to mid 80s and lows tonight
will be in the 70s.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Surface stationary front and low pressure riding along it will
continue to plague the region Saturday. Luckily, the stationary
front should begin to dissipate some Saturday night as weak
surface high pressure builds in. Weak surface high pressure
looks to hold influence over us Saturday night through Sunday
night.

Overall, short term looks impactful for Saturday morning into
Saturday afternoon and rather benign thereafter, at least PoP
wise. The concern remains for moderate to heavy rainfall
Saturday leading to flooding concerns. Plenty of low-level
moisture, showers and storms will continue to stream northwards
from the south Saturday morning; storm motions will remain
relatively slow. Any area of rain will be more than capable of
producing heavy rainfall and localized flash flooding; grounds
cold very well be saturated from Friday night. Please see the
NEAR TERM for more details.

PoPs will begin to diminish later Saturday afternoon. The I-95
corridor and areas west should actually start to see clearing
skies in the late afternoon. Highs mainly in the mid to upper
80s can be anticipated. Other than for some areas near the coast
early on, no PoP is included in the forecast for Saturday
night. Fog formation across the region is possible Saturday
night with an overall saturated boundary layer, mostly clear
skies, and very light and/or calm winds.

Heat returns for Sunday with highs mainly in the low to mid 90s
across the region. With dewpoints in the 70s, heat indices will
once again climb back up. Right now, some areas of the I-95
corridor hit advisory criteria in the forecast for Sunday;
Sunday may be the first day advisories are needed. A stray and
isolated shower is not out of the question for Sunday and Sunday
night with the proximity of the decaying front, but the
forecast mainly remains dry.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
The high heat and humidity returns for the beginning to midweek
time frame before a cold front crosses through Wednesday-
Thursday. Afternoon highs in the mid to upper 90s with dew
points in the 70s are anticipated for at least Monday and
Tuesday, maybe continuing into Wednesday depending on the timing
and placement of the mentioned cold front. With heat indices of
100-110 across the region, widespread heat headlines are
anticipated for Monday and Tuesday. Headlines may continue into
Wednesday as well. More seasonable conditions will likely return
once the cold front has crossed through.

Diurnally-driven thunderstorms are likely to occur each
afternoon, but with the lack of any forcing nearby, the threat
does not appear to be severe. Eventually, the cold front will
approach from the northwest Wednesday into Thursday, which may
result in a more widespread chance of showers/thunderstorms
across the region.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Periods of MVFR conditions will develop later today as
SHRA develop. Scattered TSRA possible, and rain may be heavy at
times, resulting in localized IFR or lower VSBYs. VFR conditions
will likely prevail at times however. S winds 5 to 10 kt. High
confidence in SHRA developing, but low confidence on when TSRA
pass over a given terminal.

Tonight...IFR conditions developing. Lingering SHRA/TSRA taper
off, then fog and stratus will remain in place. S-SE winds 5 to
10 kt. Moderate confidence overall.

Outlook...

Saturday...Sub-VFR likely with periods of heavy rain and
occasional thunder. Locally higher winds are possible in
thunderstorms. Fog lingering during the morning hours. High
confidence.

Saturday night...Sub-VFR possible due to fog formation.
Moderate confidence.

Sunday through Tuesday...Primarily VFR. A slight chance to
chance of a shower or thunderstorm on Monday/Tuesday. Otherwise,
no significant weather expected. Moderate confidence.

&&

.MARINE...
Persistent S winds 10 to 15 kt. Seas will be around 5 feet, so
will keep the Small Craft Advisory in effect through much of
today for the ocean waters. Will add the DE ocean waters to the
SCA.

VSBY restrictions in showers and fog. Rain may be heavy at
times. Scattered thunderstorms possible as well.

Outlook...

Saturday/Saturday night...SCA flag possible due to seas around
5 feet. Some fog development possible Saturday morning and
Saturday night.

Sunday through Tuesday...No marine headlines expected. Winds up
to 20 kt and seas 2-4 feet.

Rip Currents...

South to southeast winds will range from 10 to 15 mph with
breaking waves of 2 to 4 feet. With the flow slightly onshore or
parallel to the shore in New Jersey, there is a MODERATE risk
for the development of dangerous rip currents at the Jersey
Shore. For Delaware, the flow will be more onshore if not a bit
offshore. As a result, there is a LOW risk for the development
of dangerous rip currents at Delaware Beaches.

Conditions on Saturday will be similar to conditions today,
though Jersey Shore beaches in Monmouth county will have a LOW
risk, while the rest of the Jersey Shore will have a MODERATE
risk for dangerous rip currents. Delaware Beaches will once
again have a LOW risk for the development of dangerous rip
currents.

For specific beach forecasts, visit weather.gov/beach/phi

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch through Saturday afternoon for PAZ070-071-101>106.
NJ...Flood Watch through Saturday afternoon for NJZ001-007>010-012-
     013-015>019.
DE...Flood Watch through Saturday afternoon for DEZ001-002.
MD...Flood Watch through Saturday afternoon for MDZ012-015-019-020.
MARINE...Small Craft Advisory until 4 PM EDT this afternoon for
     ANZ450>455.

&&

$$

SYNOPSIS...Wunderlin
NEAR TERM...MPS/Staarmann
SHORT TERM...DeSilva/Wunderlin
LONG TERM...DeSilva/Wunderlin
AVIATION...DeSilva/MPS/Staarmann/Wunderlin
MARINE...DeSilva/MPS/Staarmann/Wunderlin