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000
FXUS61 KPHI 220824
AFDPHI

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

.SYNOPSIS...
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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. An
approaching warm front will bring a chance for some rain over
the weekend.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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Chilly conditions are occurring across the region this morning as an
expansive area of high pressure is centered over the Plains. A few
passing high clouds are present across the region but they really
haven`t had much of an effect on temps this morning. Temps generally
are in the 30s as a result of strong radiational cooling. With RH
values in the 70-80% range and dew points in the 20s outside of
Philadelphia proper, patches of frost are expected to develop over
the next 2 hours. As a result, no changes have been made to frost
headlines this morning which remain in effect until 9 AM.

For today, wall to wall sunshine is expected. Modest northwest flow
will remain across the area, resulting in sufficient mixing and
drying this afternoon. Continued to lean on the warmer/drier side of
guidance with highs in the low to mid 60s and dewpoints in the 20s,
with cooler temps near the coast due to seabreeze development. As
dry and warm conditions are expected, this may allow for a period
for fire concerns. For more details, see Fire Weather section below.

Clear skies continue tonight as ridge axis becomes elongated and
moves overhead. Another round for patchy frost is expected tonight
in similar areas as this morning due to optimal radiational cooling.
Upon collaboration with neighboring offices, will not issue frost
headlines for tonight until the current frost advisories are no
longer in effect. Lows will primarily be in the 30s with 40s along
the coast.
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&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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Surface high pressure will shift eastward to the East Coast on
Tuesday, with the high centered off the coast of the Carolinas,
while a ridge extending northward shifts offshore of the mid-
Atlantic coast. Stable atmospheric conditions with an upper-
level shortwave ridge along the East Coast will ensure another
dry day with mostly sunny skies. Expect another frosty start to
the day in areas inland from the coast and away from the urban
corridor, but less so in the Delmarva. Southerly breezes and
warm air advection aloft will result in high temperatures around
5 degrees warmer than Monday, well into the mid to upper 60s
for most areas outside of the shore and the Poconos.

Clouds will increase Tuesday night as low pressure tracking
across Quebec and northern New England swings a sharp cold front
toward our region. Showers may push southeastward down to the
coast by dawn on Wednesday. That will result in much milder
nighttime and early morning temperatures compared to the
previous few nights. Model guidance has continued to advertise
an earlier frontal passage, pushing offshore Wednesday morning.
This system continues to look quite moisture starved as well,
without a tap to moisture from the Gulf of Mexico. Rainfall
amounts should be less than a quarter-inch, and perhaps less
than a tenth of an inch, for most locations through Wednesday.
The earlier cold front passage reduces the chance for
thunderstorms somewhat, however, models are indicating
conditionally unstable conditions Wednesday afternoon post-
front, and with the mid-level trough and secondary cold front
approaching, there may still be some pop up showers with even
some rumbles of thunder in the afternoon, especially northwest
of the Fall Line. However, moisture will be really lacking by
that point, and NBM thunder probabilities are less than 10
percent, so do not have a mention of thunder in the forecast
yet. Expect warm temperatures for the most part on Wednesday, at
least southeast of the Appalachians, but accompanied by brisk
northwest winds in the afternoon and evening. Skies will clear
as high pressure quickly builds southeastward from the Great
Lakes Wednesday night, across the Northeast and Mid-Atlantic
Thursday morning. If the atmosphere can decouple and winds calm,
that could set the stage for another frosty morning.
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&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
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Expect dry weather and mostly clear skies through Friday as
strong high pressure remains in control along the Mid-Atlantic
coast. Friday morning may see yet another frosty morning inland
and outside perhaps the most urban areas. Noticeably cooler but
less breezy conditions will be in store for Thursday with highs
struggling to reach 60, followed by a gradual moderation in high
temperatures heading into the weekend. Models continue to
struggle with the forecast specifics regarding any rain over the
weekend, but the general synoptic set-up looks to be low
pressure lifting across the upper Great Lakes, with a warm front
trying to cross the Appalachians. That may bring some showers
in, particularly across eastern PA at some point over the
weekend, but at this point am not expecting a washout by any
means. Sunday may finally see some high temperatures rising
above seasonal averages, possibly into the 70s.
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&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
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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/KMIV with
potential sea breeze around 20Z. High confidence.

Monday night...VFR and SKC. Northwest winds around 5 kt becoming
light and variable. High confidence.


Outlook...

Tuesday...VFR.

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

Thursday and Friday...VFR.
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&&

.MARINE...
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No marine headlines are in effect through tonight. Northerly winds
may gust up to 15-20 kt this morning, before ultimately settling out
of the south-southeast around 5-10 kt through early Tuesday morning.
Seas around 2-3 feet.


Outlook...

Tuesday...Southerly winds increasing to 10-15 kt in the
afternoon with some gusts around 20 kt possible. Seas 3 to 4 ft.

Wednesday...Small Craft Advisory conditions likely, at least due
to seas. SW winds around 15 kt gusting to 25 kt, shifting to
the W/NW later in the day as a cold front swings through. Seas 5
to 6 ft.

Thursday...SCA possible early in the morning due to lingering
elevated seas. Diminishing NE to E winds. Seas 3 to 5 ft.

Friday...Easterly winds 10-15 kt. Seas 2 to 3 ft.
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&&

.FIRE WEATHER...
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A dry airmass will engulf the region today. Northwest winds will
generally be around 10-15 mph this afternoon. Although these winds
are not all that strong, surface dew points are anticipated to mix
down into the low to mid 20s. This will result in Min RH values in
the 20-25% range across E PA and NJ and 25-30% range across E MD and
DE. We will be in contact with our partners this morning to
determine if a SPS is needed.
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&&

.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
SHORT TERM...AKL/Dodd
LONG TERM...AKL/Dodd
AVIATION...Dodd/DeSilva
MARINE...Dodd/DeSilva
FIRE WEATHER...PHI STAFF
TIDES/COASTAL FLOODING...PHI STAFF