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000
FXUS61 KPHI 220510
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
110 AM EDT Mon Apr 22 2024

.SYNOPSIS...
High pressure extending eastward from the Midwest to the Mid-
Atlantic will continue to build eastward toward the East Coast
through Tuesday. A cold front will swing through our region on
Wednesday, followed by another area of high pressure pushing
southeastward from the Great Lakes Thursday and Friday. Chances
for rain potentially return next weekend.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1:00AM...Conditions remain tranquil but chilly. Cloud
cover with the exiting low pressure has moved off the coast
leaving just some scattered high clouds passing over
Pennsylvania and northern New Jersey. These should gradually
work their way eastward toward the coast with time early this
morning. Otherwise, the only other thing to note is that
temps have fallen quicker than expected, so have adjusted temps
for the next several hours. Overall, lows shouldn`t differ much
from what was previously forecast.

Previous discussion remains per below:

A weak cold front will pass north of the region late tonight as
low pressure tracks across Canada. Surface high pressure over
the Central Plains builds east tonight, and then will become
elongated over the East Coast Monday afternoon.

Outside of the urban corridor, radiational cooling conditions
are likely to develop. Lows will drop into the 20s in the
southern Poconos, and in the low 30s for most areas north and
west of the I-95 corridor. Lows will drop into the mid and upper
30s elsewhere. Patchy frost and areas of frost will look to
develop for many locations across the region tonight except
immediate coastal and urban areas. The spring Frost/Freeze
program has not stared for Carbon and Monroe counties in PA, but
it has started for the rest of the forecast area. A Frost
Advisory is now in effect for all our NJ counties (except
coastal areas), New Castle County in DE, and all our eligible PA
counties with the exception of Philadelphia County.

Abundant sunshine on tap for Monday. A westerly flow will
develop over the area, so will side on the warmer side of model
guidance and run with the NBM90 for highs generally in the low
to mid 60s, but cooler along the coasts.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
High pressure remains in control for the first half of the
short term forecast period as it becomes centered over the area
Monday night. Patchy frost will be possible again as
temperatures fall into the 30s outside the immediate I-95
corridor and coastal areas. This potential development will be
aided by the light to near calm winds with the high overhead.
However, dew points look to be on the drier side in the upper
20s to low 30s which should prevent widespread frost
development.

Tuesday looks to be the warmest day of this week as light
south-southwesterly flow returns with the high shifting
offshore. Temperatures look to rise unto the upper 60s to right
around 70 for most locations (high temps right around 60 at
higher elevations and along the immediate coasts of NJ/DE).

Our attention then turns to the next approaching low pressure
system which will begin to push into the region Tuesday
night/early Wednesday morning. The most significant change to
the forecast with this system has been the reduced likelihood of
seeing any thunderstorm development. While we still cannot
completely rule it out, chances are now less than 15 percent
areawide as the front appears to be arriving earlier in the day
which will reduce available surface-based instability. If a
thunderstorm were to develop, the most likely location remains
northwest of the I-95 urban corridor, where the best mid-upper
level forcing will be. Overall, the system still appears to be
rather dry with QPF likely less than a quarter of inch for most
locations. A tight pressure gradient and mixing down of stronger
winds will lead Wednesday to be breezy with gusts around 25-35
mph. Temperatures will again rise into the upper 60s to near 70
mid-day Wednesday before falling after frontal passage Wednesday
evening.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
After the passage of the cold front on Wednesday, high pressure
will push back into the region Wednesday night and influence the
region through at least Friday night. As such, dry conditions
will resume across the region Wednesday and continue through the
end of the work week. Temperatures will gradually warm through
this period though remaining below normal.

The next opportunity for rain in the region could be as early as
Saturday or Sunday. However, this remains highly uncertain with
global model suites split on potential solutions. Latest
ECMWF/CMC indicate the high and a building upper-level ridge
will setup a block over or to the east of the region and prevent
a developing low over the Midwest from encroaching on the
region while the GFS brings the low further east with rain
chances along with it. At this time, given the uncertainty, did
not stray too far from NBM guidance but wouldn`t be surprised
if PoPs were reduced to be less than the 30-40% they stand at
right now with the next forecast cycle.

&&

.AVIATION /05Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Through 12Z...VFR with a few high clouds. Northwest winds
around 5 kt becoming light and variable at times. High
confidence.

Monday...VFR. Mostly SKC, especially in the afternoon. Northwest
winds around 7-12 kt. Winds may shift to Southeast at KACY with
potential sea breeze around 20Z. High confidence.

Outlook...

Monday Night and Tuesday...VFR.

Wednesday...MVFR to possibly IFR conditions at times, as a cold
front brings showers and a wind shift from southerly to W/NW.

Thursday and Friday...VFR.

&&

.MARINE...
Sub-Small Craft Advisory conditions on tap through Monday.
NW/NNW winds generally 10-15 kts becoming SE Monday afternoon.
Seas 2 to 3 ft.

Outlook...

Monday Night through Tuesday...Sub-SCA conditions expected with fair
weather.

Wednesday...Small Craft Advisory conditions possible (30-40%),
most likely Wednesday night. Southerly winds around 15 kt
gusting to around 20 kts, shifting to the W/NW later in the day
as a cold front swings through. Gusts may increase to around 25
knots following the wind shift. Seas build 4 to 5 ft Wednesday
night.

Thursday through Friday...Sub-SCA conditions expected with fair
weather.

&&

.FIRE WEATHER...
A dry air mass will overspread the region on Monday. West winds will
generally be around 10 mph in the afternoon. Although these winds
are not strong, it will be quite dry. Surface dew points will
mix down into the mid 20s, and Min RH values will range from 20
to 25 percent.

&&

.TIDES/COASTAL FLOODING...
A prolonged period of southerly flow will develop during the
middle of the week ahead of a cold front that will push offshore
on Thursday. This is forecast to result in surge values rising
to around 1-2 feet above normal along Delaware Bay, the tidal
Delaware River, and Chesapeake Bay. With the full moon
occurring on Tuesday, 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 PAZ060>062-070-
     101>106.
NJ...Frost Advisory until 9 AM EDT this morning for NJZ001-007>010-
     012-013-015>023-027.
DE...Frost Advisory until 9 AM EDT this morning for DEZ001.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...AKL
NEAR TERM...DeSilva/MPS/Wunderlin
SHORT TERM...AKL
LONG TERM...AKL
AVIATION...AKL/DeSilva/MPS/Wunderlin
MARINE...AKL/MPS/Wunderlin
FIRE WEATHER...WFO PHI
TIDES/COASTAL FLOODING...WFO PHI