187
FXUS61 KPHI 050857
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
457 AM EDT Wed Jun 5 2024

.SYNOPSIS...
An area of low pressure approaches from the northwest late today
with a warm front moving through the region this evening. A
cold front follows tomorrow crossing through the region on
Thursday into Thursday night. Heading into the weekend unsettled
weather looks to persist into early next week as several
shortwaves pivot around the upper low over southern Canada.

&&

.NEAR TERM /THROUGH TONIGHT/...
Low marine stratus has begun to advect inland resulting in some
areas of fog and mist which will continue through the pre-dawn hours
this morning. Fog and low stratus should begin to lift and mix out
by mid-late morning which will give way to mostly cloudy skies.

Unfortunately, the pleasant stretch of weather we encountered early
in the week is beyond us. A warm front will be situated to our south
and west this afternoon which will eventually begin to make some
progress north across our area this evening. The warm front should
completely lift north of our area by Thursday morning. The front
will be accompanied by some shortwave energy aloft which will
increase the forcing of ascent across the region. As a result, an
initial batch of showers and thunderstorms are expected to develop
and approach from the southwest and overspread the rest of the
region this evening. For most of the overnight period, light to
moderate rain (with embedded thunder) is expected, giving way to
just some spotty showers/storms by early Thursday morning as
depicted by most of the hi-res guidance.

Although mostly cloudy to overcast skies will encompass much of the
region today, a very moist airmass will be in place. Thus, there is
a fairly high chance for some thunderstorms this afternoon into
tonight. Despite limited surface heating, a narrow corridor of
SBCAPE in excess of 1000 J/kg this afternoon will be in place across
the Delmarva which will lie in close proximity to the warm front.
However, mid-level lapse rates are weak (only near 6.5C/km) which
will likely hinder development of strong updrafts. As a result, the
Storm Prediction Center has upgraded the Eastern Shore of Maryland
into a Marginal Risk (Level 1/5) for severe weather today. The rest
of the area lies in just a general thunderstorm risk. The main
threat in the highlighted area will be damaging winds. With backed
SE surface winds near the warm front, model soundings due show some
curved hodographs in the lowest 0-3km. So while there is a non-zero
chance of a tornado, the greater potential looks to lie outside of
our area.

PWATs will also be near/in excess of 2.0 inches later this afternoon
into tonight, so heavy downpours are likely, especially in any
thunderstorm that occurs. Currently, WPC has the western half of our
forecast area highlighted within a Marginal Risk (Level 1/4) risk
for excessive rainfall. However, flash flooding does not appear to
be a threat as ground soils are relatively dry and the storm motion
is quite quick. QPF values through tonight are forecast to be around
0.5-1.0 inches, locally higher in thunderstorms.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
A deep upper trough will be accompanied by a nearly vertically
stacked low pressure system which will be meandering around
southern Canada and the northern Great Lakes during the period.
This will bring a cold front through by Thursday into Thursday
evening.

Guidance continues to highlight the likelihood of a concentrated
set of showers and thunderstorms moving through the region
Thursday afternoon into the evening. CSU-MLP guidance still
indicates a 5-14% chance of severe weather on Thursday with the
most likely threat being hazardous wind. Showers and
thunderstorms will cease on Thursday night as the cold front
moves offshore.

Highs will be in low/mid 80s on Thursday dependent on the
amount of clearing. Thursday night lows will be cooler in the
upper 50s to mid 60s.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
The long term period is forecast to be generally unsettled
through early next week. The aforementioned upper trough and low
will meander across southern Canada and the northern Great
Lakes through the weekend. As it does so, multiple shortwaves
will round through the upper trough resulting in several rounds
of showers and occasional thunderstorms through the weekend into
next week. While no singular day appears to be a washout, there
will be quite a bit of showers around, more likely north and
west with drier conditions south and east. The highest
probability of precipitation will be during the afternoon hours
as diurnal heating allows instability to be maximized.

Temperatures during this period will remain quite seasonable for
early June with a mix of 70s/80s during the day and 50s/60s at
night.

&&

.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through 12Z...VFR to continue through about 08Z before low clouds
and patchy fog arrives as the marine layer moves inland.
Still anticipate that it should primarily be low marine stratus for
most terminals dropping to IFR/MVFR. For KACY/KMIV and potentially
KILG, fog may impact these terminals, resulting in periods of
IFR/LIFR. Southeast winds around 5 kt or less becoming light and
variable at times. Low confidence overall, especially with regard to
timing of lowering CIGs/VSBYs.

Today...LIFR/IFR/MVFR CIGs should lift to VFR at all terminals by 15-
16Z. Another round of lowering CIGs down to MVFR are expected later
in the day as rain showers and isolated thunderstorms move into the
region. South-southeast winds around 5-10 kt. Moderate confidence.

Tonight...All terminals should encounter lowering CIGs and
decreasing VSBYs as heavier rain moves in this evening. Heaviest of
rain should continue through about 06-08Z, before lifting north and
east of the region. Still anticipate lower CIGs/VSBYs to persist
after rain exits. South-southwest winds around 5-10 kt. Low
confidence.

Outlook...

Thursday through Thursday night...Sub-VFR conditions probable
with showers and thunderstorms.

Friday through Saturday...Primarily VFR expected with sub-VFR
conditions possible. A chance of a shower or thunderstorm each
afternoon.

&&

.MARINE...
No marine headlines are expected through tonight. Locally dense
marine fog this morning will give way to fair weather early this
afternoon. Chances for showers and thunderstorms increase late this
afternoon into tonight. South-southeast winds around 10-15 kt today
increasing up to 15-20 kt tonight. Localize higher gusts up to 22-23
kt possible. Seas of 2-3 feet increasing to 3-4 feet.

Outlook...

Thursday and Thursday night...Sub SCA expected, however winds
may gust around 20+ kt on Wednesday night into Thursday. Seas
around 3-4 feet. Showers likely with a chance of thunderstorms.

Thursday night through Saturday...No marine headlines expected.
Winds generally around 10-15 kt with seas of 2-4 feet. Slight
chance of a shower or thunderstorm each afternoon.

Rip Currents...

A LOW risk for the development of rip currents is in place for
both New Jersey and Delaware beaches for today. Winds will be
on onshore from the SSE, but only around 10-15 mph with 1-2
foot waves and a 9 second period.

For Thursday, SSW winds around 10-15 mph will parallel the
shoreline for NJ and offshore for DE beaches. With breaking
waves of 2-3 feet, a medium period swell, and a new moon, the
risk for rip current development is MODERATE for New Jersey
beaches and LOW for Delaware beaches.

Rip currents occur often in the vicinities of jetties and
piers. Utilize any guarded beaches if venturing out into the
water. For specific beach forecasts, visit weather.gov/beach/phi

&&

.TIDES/COASTAL FLOODING...
With sustained onshore flow expected through at least Wednesday
and the approaching New Moon on Thursday, there will likely be
some tidal flooding for much of our coastal region.

For today and tomorrow, the threat for widespread minor
flooding looks to increase as winds strengthen then turn and
become shore parallel on Thursday, potentially trapping water
along the coast. Recommend to continue to monitor upcoming high
tides and make adjustments to the forecast accordingly.

Overall, the threat for tidal flooding appears to be lower
along the Chesapeake Bay than elsewhere in the region but by the
early morning high tide Thursday, water levels may also
approach spotty minor.

&&

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

&&

$$

SYNOPSIS...Deal
NEAR TERM...DeSilva
SHORT TERM...Deal/MPS
LONG TERM...Deal/MPS
AVIATION...Deal/DeSilva
MARINE...Deal/DeSilva
TIDES/COASTAL FLOODING...WFO PHI