772
FXUS61 KPHI 191911
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
311 PM EDT Sat Oct 19 2024

.SYNOPSIS...
High pressure remains across our area before weakening and shifting
offshore Tuesday into Wednesday. A cold front crosses our area
Wednesday night into early Thursday morning, then sprawling high
pressure builds back in for Friday and Saturday adding to our
current dry spell.

&&

.NEAR TERM /THROUGH SUNDAY/...
A gradual warming trend persists through the near term with a very
dry airmass remaining in place under sunny/clear skies.

The strong subsidence from the upper-level ridging, sunny skies, and
very light to calm winds should promote efficient boundary layer
mixing into the afternoon. Afternoon high temperatures are forecast
to be mainly in the low 70s area wide, although the immediate coast
and higher terrain will stay in the mid to upper 60s.

BUFKIT and raw model dewpoints indicate we should see dewpoints
mixing out into the mid 30s today. Fortunately we will not have the
downsloping component at play as we did on Friday, and dewpoints are
a bit higher due to the airmass modification. So dewpoints in the
30s combined with temperatures in the low 70s should get us relative
humidity values around 25% area wide, perhaps as low as about 20%
locally in some isolated spots. See the Fire Weather section below
for more details.

For tonight, low temperatures will range from the upper 30s to low
40s in most areas with winds becoming calm. Again, cannot rule out
some patchy frost in the usual colder spots, but the dry air and
marginal temperatures should preclude a need for any frost headlines
anywhere where the growing season continues.

On Sunday, the story will largely be the same with clear skies and
dry conditions. However, with the upper-level ridge weakening, more
west-southwesterly flow returns aloft with winds at the surface out
of the west, though remaining relatively light around 5-10 mph. The
result will be continued slow air mass modification with slightly
warmer temperatures and slightly higher dew points. Highs on Sunday
are forecast in the mid-upper 70s with dew points in the upper 30s
to low 40s.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
The dry conditions continue with even some near record warmth
possible early next week.

An upper-level ridge remains in place into Tuesday before it starts
to shift east and also flattens some on the north side during
Tuesday. An expansive area of surface high pressure that has been
over our area will weaken and also shift eastward and more offshore.
As this all occurs, an upper-level trough sliding across the Midwest
to the mid-Mississippi Valley will shift eastward through Tuesday.
Low-level warm air advection will get boosted some through Tuesday
as the flow turns more southerly beneath the gradually departing
ridge aloft and surface high pressure.

Given that the air mass continues to modify, Sunday night will be
chilly but not as cold as several recent nights. This is banking on
the dew points rebounding some more at night to keep temperatures
from dropping as low. Daytime temperatures then warm quite a bit
(well above average) Monday and Tuesday, especially with the
continued very dry ground, with many areas potentially getting into
the low 80s especially Tuesday. Record high temperatures are lower
Tuesday for several sites compared to Monday and therefore some
places could near record high temperatures Tuesday afternoon. The
surface wind however should be more south or southeast Tuesday and
that should keep it cooler closer to the coast. Otherwise, the dry
stretch of weather continues given the upper air pattern with
sinking air.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Summary...Overall the dry conditions continue; Temperatures start
above average then drop closer to average.

Synoptic Overview...An upper-level trough is forecast to slide
across the Northeast and northern Mid-Atlantic regions Wednesday
into Thursday, then the flow turns more zonal aloft into the
weekend. At the surface, a cold front moves through Wednesday night
into early Thursday morning followed by sprawling high pressure
building in Friday and Saturday.

For Wednesday and Thursday...An upper-level trough is forecast to
quickly slide across the Northeast and northern Mid-Atlantic regions
during this time frame. The bulk of the forcing moves across New
England with it much weaker into our area. In addition, the moisture
return is forecast to be more limited ahead of and with a cold
front. The cold front itself is currently forecast to cross our area
Wednesday night and be offshore early Thursday morning. A few
showers or some sprinkles are possible with the cold front across
mainly the northern areas, and while we really need rain
unfortunately this looks to be a dry frontal passage for most if not
all of our area. Maintained some slight PoPs, for now, across the I-
80 corridor later Wednesday night given that some weak forcing may
glance this area. Otherwise, sprawling surface high pressure starts
to build closer to our area during Thursday. Some mild air holds on
ahead of the cold front Wednesday, then turning much cooler Thursday
in the wake of the front. A pressure gradient is also forecast to
tighten Thursday in the wake of the cold front and ahead of high
pressure, and this will result in a gusty northwesterly wind on
Thursday before it diminishes at night.

For Friday and Saturday...A more zonal flow aloft is currently
forecast for this time frame with sprawling surface high pressure
becoming nearly parked right over our region. This results in
continued rather dry conditions and little to no clouds.
Temperatures are forecast to be much closer to average for this time
of year.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Remainder of Today...VFR/SKC. For most sites, variable to locally
calm winds. For PHL, a river breeze looks to have developed, so
maintained TEMPO ground for a southerly wind direction this
afternoon. At ACY, easterly winds near 5-7 kts. High confidence in
prevailing conditions.

Tonight...VFR/SKC. Winds mostly calm. High confidence.

Sunday...VFR/SKC. Winds becoming westerly around 5 knots. High
confidence.

Outlook...

Sunday night through Wednesday...VFR.

Thursday...VFR. Northwesterly winds could gust up to 25 knots
during the day before significantly diminishing at night.

&&

.MARINE...
Small Craft Advisory remains in effect for all Atlantic coastal
waters through tonight. Northeast winds gradually lessening and
becoming variable around 5 kts tonight. Seas across the Atlantic
waters ranging from 4-6 feet, lessening into tonight. Seas will
eventually fall below 5 feet by around daybreak Sunday. No further
marine headlines for Sunday are expected once seas fall below 5
feet. Aside from the elevated seas, fair weather is expected.

Outlook...

Sunday through Wednesday...The conditions are anticipated to be
below Small Craft Advisory criteria.

Thursday...Small Craft Advisory conditions possible in the wake of a
strong cold front.

&&

.FIRE WEATHER...
Very dry conditions are expected again this afternoon with forecast
minimum relative humidity values near 20-30% across much of the
area. Fortunately for today, variable winds will be around 5 mph
at most and even locally calm for much of the day. High temperatures
will be in the low 70s in most areas under sunny skies. Given
the very light winds, a Special Weather Statement for fire spread
danger is not expected.

Dry conditions are forecast to persist through Sunday with minimum
relative humidity values around 25-35%, and winds will remain light
around 5 mph for much of the area. This should help limit fire
spread potential despite the persistently dry air. Minimum relative
humidity is forecast to recover into the 35-45% range into early
next week, although with increasing temperatures into the upper 70s
to low 80 degrees through Wednesday.

&&

.CLIMATE...
Some near record warmth possible Tuesday. Here are the current
record high temperatures for October 22...

Site        Record High Temperature/Year
----        ----------------------------
PHL          83 in 1920
ABE          84 in 1979
RDG          83 in 1979
MPO          81 in 1979
ILG          81 in 1979
GED          83 in 2020
TTN          83 in 1979
ACY airport  83 in 1979

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 AM EDT Sunday for ANZ450>455.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...AKL
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...AKL/Gorse
MARINE...AKL/Gorse
FIRE WEATHER...PHI
CLIMATE...PHI