Flash Flooding in Pennsylvania, June 23, 2023

Area Forecast Discussion
National Weather Service Mount Holly NJ
332 PM EDT Fri Jun 23 2023

.SYNOPSIS...
An overall unsettled weather pattern will persist through next week.
The upper level trough centered near the southeastern states will
gradually lift northward through the mid Atlantic region this
weekend. Another area of low pressure slowly moves in from the
northwest on Monday, slowly dropping a cold front through our region
Tuesday. This front may stall near the area through much of next
week.

&&

.NEAR TERM /THROUGH SATURDAY/...
Showers and thunderstorms have started to move into the area this
afternoon. Looking at 12z observed soundings, ACARS soundings from
KPHL, and model guidance, we have become a bit more concerned about
the severe potential for today. Soundings show a good amount of
veering with height, especially in the low-levels. Combined with
1000-1500 J/kg of MLCAPE, and moderate forcing, there certainly is a
threat for a few strong to severe thunderstorms. The main hazard
will be gusty winds, but cannot rule out the possibility of a
tornado, especially with slightly rightward hooking hodographs
showing up in the soundings. SPC has added a Marginal Risk basically
from Philadelphia on south.

In addition to the severe threat, there will be the potential for
flash flooding. PWAT values are around 1.9-2.0 inches across most of
the area. Incoming downpours will certainly pack a punch and have
the capability to produce rates anywhere from 1 to 3 inches per
hour. Main concerns are within the urban corridor, and the primary
area we are watching based on radar trends and short range guidance
is from Wilmington to West Philadelphia into Bucks County up until
the NJ/PA border.

Showers and thunderstorms will gradually wane into the overnight
hours with the severe and hydro threats diminishing. It won't clear
out completely with scattered showers and isolated thunderstorms
remaining in the area through the night. When it is not raining, it
will be overcast and muggy. This will keep low temperatures
elevated, mainly in the upper 60s, with some spots staying at/above
70.

The trough continues to push east towards our region, with another
round of showers and thunderstorms expected for Saturday afternoon.
Main concerns remain to be poor drainage flooding as storm motion
vectors still look on the slow side. Severe threat also looks less
compared to today with less instability and shear overall.
Temperatures will climb into the upper 70s/low 80s.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
Shower and thunderstorm activity wanes into Saturday evening with
the loss of daytime heating, and the latter part of the night looks
dry for most. Lows get down generally into the mid 60s.

Sunday should be the relatively drier day of the weekend, though
still expecting some pop-up showers and thunderstorms in the
afternoon. Best chance to see any convection will be north and west
of Philadelphia, but generally expecting more scattered activity
compared to Saturday. Temperatures will climb into the mid 80s.
Sunday night looks more on the quiet side now as the trough that
brought active weather for the weekend finally moves out. The
reprieve looks to be brief though as the region will be in middle of
two systems during that timeframe. Still cannot rule out a lingering
shower. It will be an otherwise warm and muggy night with lows
generally in the 65 to 70 range.

In the wake of our departing weekend trough, a more amplified trough
will be digging through the Great Lakes, potentially taking on a
negative tilt as it gets to our region. An area of low pressure will
slide by to the northwest, dropping a cold front through our region.
Monday more than any day in the extended looks to have some severe
weather potential due to strong forcing and sufficient instability.
Flooding with localized flash flooding will be a threat as well but
this will also depend on how much rain falls over the weekend and
where the heaviest is. Also, still a way out with differences
remaining among guidance. Monday also looks to be the warmest day
with temperatures getting into the mid to upper 80s with the
potential for some spots to hit the 90 mark. It will also continue
to be quite humid with Max Apparent Temps making it feel more like
the low to mid 90s across the urban corridor southward into
Delmarva.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
The overall pattern does not look to change much through most of
next week as an upper level trough lingers in the east with a
continuing deep layer southerly flow. This will keep things
unsettled through at least midweek with Tuesday and Wednesday
featuring additional rounds of showers/storms that could once again
be fairly widespread. Beyond this time the trough may finally try to
lift out by the end of next week but forecast confidence by this
time is fairly low. So at this time we will keep at least low
chances (around 30 percent) for showers/storms in the forecast right
through next Thursday and Friday.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
The following discussion+-n is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Rest of Today...A warm front lifting north will gradually increase
conditions briefly before scattered showers and thunderstorms move
in. As of 20z, the warm front is right around KPHL/KPNE and we have
seen conditions turn VFR at KMIV/KACY where the front has passed.
Confidence remains low on how quickly the front moves north.
Otherwise, for this afternoon, periods of showers and thunderstorms
will move through for the afternoon and evening, reducing visibility
down to as low as 1SM. Periods of showers and thunderstorms will
continue through about 02z. Winds will gradually veer as the
afternoon goes on, going from easterly to a more south/southeast
direction, still around 5-10 kt with the exception of KACY/KMIV,
where some gusts in the mid to upper teens are possible.

Tonight...A mix of IFR/LIFR conditions are expected in the wake of
the front with some scattered light showers for most of the night.
Confidence remains low on timing and extent of restrictions though.
Winds will generally be out of the south around 5 kt or less, though
some spots will likely go light and variable. Low confidence.

Saturday...Conditions lift to MVFR by the mid to late morning and
should improve to VFR for the afternoon prior to the arrival of
showers and thunderstorms. Brief IFR restrictions possible with any
afternoon thunderstorms. South/Southwest winds around 5-10 kt. Low
confidence in timing, moderate confidence in occurrence.

Outlook...

Saturday Night...Showers/storms diminishing through the evening
but there could still be sub VFR restrictions lingering
overnight due to areas of low stratus and mist/fog. Winds light
and variable but generally favoring a W/SW direction. Low
confidence.

Sunday through Sunday Night...It should be VFR the majority of
the time though brief restrictions possible with any
showers/thunderstorms in the afternoon. Storms expected to
subside at night. SW winds around 5-10 kt during the day turn S
to SSE at night. Moderate confidence.

Monday through Monday Night...Likely VFR to start, but afternoon and
evening showers and thunderstorms will potentially result in
restrictions. Southerly winds around 10-15 kt during the day will
decrease to around 5-10 kt overnight. Moderate confidence.

Tuesday through Tuesday Night...Sub-VFR conditions likely with
periods of showers/thunderstorms, mainly in the afternoon into
the early evening. Southerly winds around 10-15 kt, turning SW
at night. Low confidence.

Wednesday...Sub VFR possible at times due to scattered
showers/storms, mainly during the afternoon into the early
evening. Southwest winds around 10 knots. Low confidence.

&&

.MARINE...
No marine headlines anticipated through Saturday. Periods of showers
and thunderstorms likely however which could result in brief periods
of gusty winds and frequent lightning. South/Southeasterly winds
around 10-15 kt and seas 2 to 4 feet.

Outlook....

Saturday night through Sunday Night..No marine headlines
anticipated. Southerly winds around 10-15 kt with seas 3 to 4
feet. Periods of showers and thunderstorms likely on the waters.

Monday through Tuesday...SCA conditions possible beginning by
Monday afternoon. Southerly winds around 15-20 kt with gusts
nearing 25 kt. Seas 4 to 6 feet. Periods of showers and
thunderstorms likely on the waters.

Wednesday...Winds should be diminishing below SCA levels but
seas are forecast to still be around 5 to 7 feet.

&&

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

&&

SYNOPSIS...Fitzsimmons/MJL
NEAR TERM...Hoeflich
SHORT TERM...Fitzsimmons/MJL
LONG TERM...Fitzsimmons/MJL
AVIATION...Fitzsimmons/Hoeflich
MARINE...Fitzsimmons/Hoeflich

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Special Weather Statement
National Weather Service Mount Holly NJ
208 PM EDT Fri Jun 23 2023

DEZ002-003-231845-
Inland Sussex DE-Kent DE-
208 PM EDT Fri Jun 23 2023

...Strong thunderstorms will impact portions of northwestern Sussex
and southeastern Kent Counties through 245 PM EDT...

At 208 PM EDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Andrewsville to near Ellendale to near
Milton. Movement was northeast at 35 mph.

HAZARD...Wind gusts up to 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Milford, Harrington, Ellendale, Bowers, Viola, Big Stone Beach,
Andrewsville, Felton, Greenwood, Frederica, Houston, Farmington and
Riverview.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3904 7559 3906 7538 3900 7523 3874 7535
      3875 7553 3876 7572
TIME...MOT...LOC 1808Z 212DEG 28KT 3883 7564 3883 7548 3882 7535

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

MLB

Special Weather Statement
National Weather Service Mount Holly NJ
239 PM EDT Fri Jun 23 2023

DEZ002-231915-
Kent DE-
239 PM EDT Fri Jun 23 2023

...Strong thunderstorms will impact portions of Kent County through
315 PM EDT...

At 239 PM EDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Sandtown to near Rising Sun-Lebanon to
near Big Stone Beach. Movement was northeast at 35 mph.

HAZARD...Wind gusts up to 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Dover, Smyrna, Camden, Clayton, Cheswold, Bowers, Woodside, Viola,
Hartly, Rising Sun-Lebanon, Hazlettville, Dover Base Housing, Dover
Speedway, Sandtown, Rising Sun, Big Stone Beach, Wyoming, Felton,
Frederica and Kenton.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 3900 7549 3898 7573 3929 7574 3930 7569
      3929 7568 3929 7565 3931 7562 3931 7558
      3934 7542 3926 7525 3895 7528
TIME...MOT...LOC 1839Z 212DEG 32KT 3898 7570 3906 7550 3903 7530

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

MLB

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