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000
FXUS61 KPHI 230658
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
258 AM EDT Tue Apr 23 2024

.SYNOPSIS...
The center of high pressure generally builds to our south today,
then a cold front will cross our region during mostly Wednesday
morning. High pressure then arrives from the Great Lakes Thursday
before shifting to our northeast and east during Friday. A warm
front should lift north of our area late Saturday, then a cold front
gradually approaches later Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Latest analysis depicts an elongated ridge of surface high
pressure extending from the Southeast northeastward into
Atlantic Canada. Dry air, mostly clear skies and light winds
have promoted strong radiational cooling and we should have
fairly widespread frost early this morning, with frost and
freeze headlines remaining in effect until 9 AM. Otherwise, the
day should dawn sunny and calm.

Incoming system still over the central Plains and upper Midwest
will begin to spread some high clouds overhead today, but
otherwise, should be fairly sunny. With warm advection
developing ahead of the system on strengthening southerly flow,
expect highs to rise 5-10 degrees above yesterday`s readings,
which will feel quite nice after the chilly morning. Winds will
be a little gusty, perhaps up to 20 mph, but not much different
from yesterday.

The approaching system will further increase clouds with a
steady southerly flow tonight. This will help keep temps much
milder, with lows likely 10-15 degrees higher than this morning,
mostly 40s and low 50s. As the system gets closer late at night,
a few shower may move into the region, but overall not expecting
much, so kept overnight POPs in the slight chance to low-end
chance range.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
An upper-level trough is forecast to swing across our region during
the day Wednesday. This will drive a cold front across our area
during mostly Wednesday morning. This system looks to have limited
moisture with it, without a tap to Gulf of Mexico moisture, and
therefore rainfall amounts are forecast to be very light. While the
main cold front shifts offshore by early afternoon, a secondary cold
front or trough (dew point front) may arrive by late afternoon.
Since the cold front continues to look faster, more drying is
forecast to be working into the area through the afternoon. This
would tend to decrease the instability, however the model forecast
soundings show some weak instability present in the afternoon. The
overall forcing though may be on the weaker side, however the model
forecast soundings also show lowering freezing levels and steepening
low level lapse rates. If a heavy shower or thunderstorm were able
to develop in the afternoon, then locally gusty winds and small hail
will be possible. Overall though with the extent of the drying
forecast from about late morning through the afternoon, the thunder
potential looks to be on the low side. Mild temperatures Wednesday
for most of the area, however a strengthening/gusty west to
northwest wind will be in place in the afternoon and evening. The
sky will clear especially later in the day as high pressure quickly
builds southeastward from the Great Lakes Wednesday night, across
the Northeast and Mid-Atlantic Thursday morning. If the lower levels
can decouple and winds become calm, a frosty early Thursday morning
would be quite possible especially the more favorable locations like
interior New Jersey and eastern Pennsylvania north and west of the
Fall Line.

A notable colder and dry air mass will be in place Thursday despite
a mainly sunny sky with high temperatures mostly in the 50s. An
onshore wind will also keep it even cooler along the coastal areas.
Thursday night may feature more areas of frost with temperatures
dropping into the 30s for much of the area.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Summary...Cool to start then a significant warm-up probable over the
weekend and early next week. Some shower chances later in the
weekend and/or early next week.

Synoptic Overview...As an upper-level trough shifts to our east to
start Friday, a building ridge arrives from the west as an upper-
level trough lifts across the Plains and into the Midwest through
Sunday. As the influence of the upper-level trough gets closer
Sunday night and Monday, the ridge shifts to our east. The timing of
this however is less certain as the upper-level trough in the Plains
may become a closed low which tend to be slower moving (may be two
separate systems). This will also have an impact on our
precipitation chances Sunday and Monday. The overall pattern though
suggests that a much warmer air mass will overspread our region
mostly during the second half of the weekend and early next week.

For Friday and Saturday...Surface high pressure is currently
forecast to be centered across coastal New England to start Friday,
then it shifts eastward as a building ridge starts to arrive from
the west. This will initially keep a cool air mass across our
region, however better warm air advection kicks in Saturday as more
of a southerly return flow starts to set up. In addition, a warm
front should lift to our north later Saturday. While a few showers
cannot be ruled out with this warm front, the probability looks to
be on the low side at this point. After a mainly sunny Friday,
clouds should be on the increase some during Saturday within the
increasing warm air advection regime plus ahead of and with the warm
front. The timing of this warm front looks to be driven by a lead
upper-level trough or closed low that lifts across the Midwest
which also has a surface low with it.

For Sunday and Monday...As an upper-level trough continues to lift
up across the Plains and Midwest, the downstream ridge axis slides
across our region. The influence of the trough however may start to
weaken the ridge or shift it to our east into Monday. Surface low
pressure tracks across the Great Lakes Monday, and its associated
cold front may not approach our area until Monday night. The details
however will depend on the timing and amplification of the trough.
In addition, high pressure sliding east of Hudson Bay Canada later
Sunday into Monday may send a cold front down across New England and
closer to our area. As of now, that front should remain north of our
area given continued southerly flow ahead of the aforementioned
trough from the west. Plenty of warm air is therefore currently
forecast across the area, with high temperature for much of the area
in the 70s to even locally some low 80 degrees. There is some chance
for some showers and thunderstorms, especially Monday however the
probabilities look to be on the lower side as of now.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Through today...VFR. Light and variable winds early become
southerly 5-10 kts after daybreak. Gusts of 15-20 kts possible
later in the morning into the afternoon. High confidence.

Tonight...VFR. A few showers are possible late, but no
reductions in cigs or vsby expected before dawn Wednesday. Winds
southerly 5-10 kts. High confidence.

Outlook...

Wednesday...Mainly brief period of MVFR conditions possible with
also some showers.

Thursday and Friday...VFR.

Saturday...VFR overall.

&&

.MARINE...
Today, winds start below advisory levels, but will increase
through the day and likely reach Small Craft Advisory levels on
the northern half of the New Jersey coastal waters, as well as
Delaware Bay. Therefore we have issued a Small Craft Advisory
for these areas. Tonight, the gusts on the bay diminish, but on
the oceans they should increase, so SCA`s expand to all ocean
zones after midnight. Seas will also build, reaching low-end
criteria by early Wednesday morning.

Outlook...

Wednesday...Small Craft Advisory conditions.

Thursday...Small Craft Advisory conditions possible mainly in the
morning.

Friday and Saturday...The conditions are anticipated to be below
Small Craft Advisory criteria.

&&

.FIRE WEATHER...
Though there will be some moisture advection with an approaching
system, the region will remain fairly dry today. Min RH values
across the region will be in the 25-35% range, with southerly
wind gusts in 15-25 mph range. As was done for Monday, a Special
Weather Statement for increased fire danger has been issued for
today.

&&

.TIDES/COASTAL FLOODING...
A period of southerly flow will occur into Wednesday morning ahead
of a cold front. This is forecast to result in surge values rising
to 1-2 feet above normal along Delaware Bay, the tidal Delaware
River, and Chesapeake Bay. With the full moon occurring today,
astronomical tides will be maximized around this time as well. This
should result in some areas of minor coastal flooding with the
Wednesday night high tide, although the extent and exact areas that
may experience the most impact remains unclear at this time.

Coastal flooding is not currently anticipated along the Atlantic
coast, except for potentially Barnegat Bay.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Frost Advisory until 9 AM EDT this morning for PAZ070-071-104-
     106.
     Freeze Warning until 9 AM EDT this morning for PAZ060>062-
     101>103-105.
NJ...Frost Advisory until 9 AM EDT this morning for NJZ016>019-023.
     Freeze Warning until 9 AM EDT this morning for NJZ001-007>010-
     012-013-015-020>022-027.
DE...Frost Advisory until 9 AM EDT this morning for DEZ001>003.
MD...Frost Advisory until 9 AM EDT this morning for MDZ012-015-019-
     020.
MARINE...Small Craft Advisory from 2 PM this afternoon to 8 PM EDT this
     evening for ANZ430-431.
     Small Craft Advisory from 4 PM this afternoon to 6 PM EDT
     Wednesday for ANZ450-451.
     Small Craft Advisory from midnight tonight to 6 PM EDT
     Wednesday for ANZ452>455.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...RCM
SHORT TERM...Fitzsimmons/Gorse
LONG TERM...Gorse
AVIATION...Gorse/RCM
MARINE...Gorse/RCM
FIRE WEATHER...Robertson/RCM
TIDES/COASTAL FLOODING...PHI