National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 091447
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1047 AM EDT Sun Aug 9 2020

.SYNOPSIS...
High pressure will shift off shore later today. A series of weak
lows will bring chances for showers and storms starting Tuesday.
A cold front is expected to approach the region Thursday into
Friday, but may stall north of our area.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Any lingering fog is dissipating, and skies will be partly to
mostly sunny for the rest of the day.

A weak mid-level shortwave trough will cross the region this
afternoon. The lift associated with this feature is rather
weak, and moisture above the boundary layer remains lower than
what has been in place the last several days. Any showers or
storms will be isolated, so will cap PoPs at slight chance,
primarily west of the I-95 corridor.

Due to a weak low-level southwesterly flow, conditions will
begin to warm up, with highs generally in the mid to upper 80s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
The mid level short wave trough will be slow to exit the region.
However, I don`t expect showers and storms to linger much past
sunset thanks to limited instability. However, it may help to
limit the extent of fog (as compared to what we saw Sunday
morning). Although the ground remains saturated in several
locations, the lack of subsidence above the boundary layer may
help to limit widespread fog and low stratus development.
However, with low dew point depressions, patchy fog will be
possible, especially in river valleys.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Overview:

No period looks completely dry in the long term. However, it
doesn`t look like we will have widespread chances for showers
and storms until at least Thursday or Friday.

Details:

Monday...A low and mid level trough over the Ohio Valley could
bring isolated showers and storms to the western portions of our
region Monday afternoon, but most of the convection should stay
to our northwest. The warming trend continues with may locations
getting back into the lower 90s once again.

Tuesday and Wednesday...Two weak troughs ahead of the main cold
front (more on that below) could result in showers and storms
each afternoon. As mentioned by the previous shift, with
abundant low level moisture in place, even weak lift could
result in convective initiation. While highs each day should be
around highs on Monday, increasing low level moisture will
result in heat index values generally in the upper 90s.

Thursday through Saturday...There remains poor agreement among
guidance and from run to run on the details of how the pattern
will evolve at the end of the week. In the mid and upper levels,
the low over Central Canada should finally start to progress
east. However, at least one operational model shows the main
trough digging towards our region, becoming positively tilted
and stalling, which seems unlikely with the larger pattern.
Other models show that trough staying well to our north with a
weak southern stream low pressure system lifting into our region
from the mid Mississippi Valley. With so much uncertainty in how
the mid and upper level pattern will develop, other details,
including timing and how far south the cold front will get
before stalling, remain quite uncertain. However, even if the
front stalls northwest of our region, it could be close enough
to bring the next chance for a widespread rain for our region. A
this point, the most likely time period for this looks to be
Thursday into Friday. Given the uncertainty, have gone with a
blend of guidance and the previous forecast through this period.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Some BKN MVFR CIGs are sliding down the Delaware River,
so will TEMPO BKN025 until 16Z at KPHL/KPNE. Not expecting this
to persist much beyond noon. Otherwise, VFR for the remainder
of the day. Winds mostly light southwesterly, but southerly or
even southeasterly winds of 10 to 15 kt are possible behind a
sea breeze. The sea breeze is likely to affect KACY, however it
is unclear how much further inland it will reach. High
confidence on all aspects except the sea breeze.

Tonight...Starting VFR. However, another round of fog is
possible, reducing conditions to MVFR or even lower, generally
after 06Z. Light and variable winds. Moderate confidence on the
overall pattern, but low confidence on the details of the fog.

Outlook...

Monday...Mostly VFR conditions are expected. There is a slight
chance for afternoon showers and storms at KABE and KRDG.
Southwesterly winds 5 to 15 kt. High confidence.

Monday night...Mostly VFR conditions expected, but patchy fog
may result in MVFR or even IFR conditions. Light southerly
winds. Moderate confidence on most aspects of the forecast, but
low confidence on the fog potential.

Tuesday through Wednesday night...Mostly VFR conditions expected.
There is a chance for showers and thunderstorms, primarily in
the afternoon each day which could result in brief MVFR
conditions. Southerly winds up to 10 kt. Moderate confidence on
most aspects of the forecast, but low confidence on the
potential for storms at the TAF sites.

Thursday...Starting with VFR conditions. MVFR or even IFR
conditions may develop by Thursday afternoon as the chance for
showers and thunderstorms increase. Southeasterly winds 10 kt
or less. Low confidence.
-- End Changed Discussion --

&&

.MARINE...
Winds and seas should stay below Small Craft Advisory criteria
through tonight. Patchy fog is possible right along the coast
late tonight.

Outlook...

Sunday night through Thursday...Winds and seas should stay below
SCA criteria. Thunderstorms are possible, especially towards the
end of the week, which could produce locally higher winds and
waves.

Rip Currents...
There is a low risk for the development of dangerous rip
currents on Sunday and Monday. Weather conditions and waves
should be similar on both days. No precipitation is anticipated.
The wind is expected to favor the southeast and south at 5 to
10 MPH. Breaking waves are forecast to be less than 2 feet with
a medium period swell from the southeast.

&&

.EQUIPMENT...
The NOAA Weather Radio All-Hazards broadcast from Hibernia Park
Pennsylvania (Station WNG-704) remains off the air.

&&

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

&&

$$
Synopsis...Johnson
Near Term...Johnson/MPS
Short Term...Johnson
Long Term...Johnson
Aviation...Johnson/MPS
Marine...Johnson
Equipment...WFO PHI