-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 212114
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
514 PM EDT Sun Apr 21 2024

.SYNOPSIS...
High pressure extending eastward from the Midwest to the Mid-
Atlantic will continue to build steadily eastward toward the
East Coast through Tuesday, while low pressure passes off the
Carolinas today and tonight. 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 MONDAY/...
-- Changed Discussion --
Weak low pressure continues to move off the Mid-Atlantic coast
and out to sea tonight. A weak cold front will pass through 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.

Any rain over southern Delmarva or Cape May county will taper
off early this evening. Clouds associated with both the surface
low over the Mid-Atlantic and the cold front passing north of
the region will scatter out tonight. With surface high pressure
building east, skies become clear and winds will diminish.
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 look to develop,
especially for northern New Jersey and portions of southeast
Pennsylvania. The spring Frost/Freeze program has not stared for
Carbon and Monroe counties, but it has started for the rest of
the forecast area. Will go ahead and issue a Frost Advisory for
late tonight through Monday morning for the Lehigh Valley,
portions of southeast Pennsylvania, and portions of northern New
Jersey.

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.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY NIGHT 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 /21Z SUNDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Tonight...VFR. Mid clouds will scatter out this evening. SKC late
tonight. W winds 10 to 15 kt this evening, becoming NW 5 kt or less
after 06Z. High confidence.

Monday...VFR. W winds around 10 kt. 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 for tonight through
Monday. W-NW winds generally 10 to 15 kt. 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...
-- Changed Discussion --
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.
-- End Changed Discussion --


&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Frost Advisory from 2 AM to 9 AM EDT Monday for PAZ060>062-
     101>103-105.
NJ...Frost Advisory from 2 AM to 9 AM EDT Monday for NJZ001-007>009.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...AKL
NEAR TERM...MPS
SHORT TERM...AKL
LONG TERM...AKL
AVIATION...AKL/MPS
MARINE...AKL/MPS
FIRE WEATHER...MPS
TIDES/COASTAL FLOODING...Staarmann