Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 190144
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
944 PM EDT Mon Mar 18 2024

.SYNOPSIS...
A reinforcing cold front moves offshore overnight. Several
upper level disturbances and cold fronts will pass through the
region this week as surface high pressure builds to the west.
Developing low pressure approaches for the end of the week and
weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
Weak reinforcing cold front moving across the region this
evening has produced some isolated flurries across the area
near ans northwest of I-95. Latest radar trends indicate this
activity is beginning to wane, and this trend should continue
into tonight. The exception may be areas north of I-78, where
the latest hi-res guidance indicate a few more light showers or
flurries are possible overnight. Cold advection will continue
overnight. The mid-level cloud cover has begun to scatter out as
of 10 PM, however would not be surprised in some clouds persist
overnight moreso than currently forecast. Dry, colder air mass
builds in behind the front overnight with temps dropping near or
below freezing region- wide, accompanied by a persistent west
to northwest wind, resulting in wind chills deep into the 20s
for most and into the lower teens in the Poconos.

Will have some sun to start on Tuesday, but clouds then increase
quickly as warm advection gets underway ahead of the next
system. The combination of the cold air mass and return of
clouds will keep temps down on Tuesday, with few locations
managing to reach 50. Westerly winds will remain gusty as well
much of the day near 10-20 mph with gusts up to 30 mph
possible. By late afternoon, there could be enough moisture
advection to cause a few flurries or snow showers to develop in
the Poconos, but the air mass should be too dry elsewhere for
any precip. No accumulation expected.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
A weak cold front crosses through the region late Wednesday,
but no impactful weather is expected aside from conditions
becoming more conducive for fire spread (more information below
in the Fire Weather section). With that said, breezy westerly
winds will increase as the day progresses. Sustained winds near
15-25 mph are forecast with peak gusts near 35 mph possible.

Ahead of the cold front Wednesday night, weak warm air
advection will allow temperatures on Wednesday to be 5 to 10
degrees higher than Tuesday. As the cold front approaches late
in the day Wednesday, a few showers are possible primarily north
and west of the fall line. However, any precipitation (should
be mostly rain aside from the higher terrain of the southern
Poconos) will be very light, with rain amounts less than a tenth
of an inch.

In the wake of the front Wednesday night into Thursday, expect
a relatively tight surface pressure gradient. Consequently,
winds of 15 to 25 mph gusting as high as 40 mph are expected.
The other impact of the cold front is that it will be
considerably cooler. A widespread freeze is likely Wednesday
night/Thursday morning (we remain outside of the growing season
so no frost/freeze headlines are needed at this time).

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
With high pressure moving offshore Friday, return flow sets up
and temperatures begin to warm back up to normal levels for the
end of the week and weekend.

The main feature we are watching in this period is a low
developing off the coast of the southeastern U.S.. Some guidance
depicts this low lifting northeast along the coast, while
others depict it staying well to our south. If it follows
something close to the first solution, we could see our next
best chance for widespread precipitation Friday night into
Saturday. However, if it stays far enough suppressed to the
south, then precipitation should stay south of the region as
well. Given the uncertainty, stayed close to a blend of guidance
and the previous forecast in this time frame.

Regardless of the evolution of the coastal low, an upper level
trough could dig southeast towards our region at the beginning
of next week, which could mean another small chance (20%) for
precipitation across the area.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Through Tonight...VFR with BKN to OVC ceilings gradually
scattering out overnight. Winds W to NW 10-15 kts with gusts
20-25 kts through 03Z or so, diminishing to near 10 kts with
gusts 15-20 kts possible after 03Z. High confidence.

Tuesday...VFR. Winds W 10-15 kts with gusts 15-20 kts early
increasing to 10-20 kts with gusts up to 25 kts in the
afternoon. High confidence.

Outlook...

Wednesday through Saturday...VFR overall. A few SHRA or SHSN
Tuesday afternoon, and again Wednesday afternoon and evening
could result in brief sub-VFR conditions. A prolonged period of
W-NW winds will range from 15 to 20 kt with 25 to 35 kt gusts.

&&

.MARINE...
SCA through Tuesday with persistent west to northwest winds
10-20 kts with gusts to 30 kts. Seas mainly 2-4 ft.

Outlook...

Should be a brief lull in SCA conditions Tuesday night into
Wednesday morning, before SCA conditions develop again late
Wednesday through the day on Thursday. Winds and seas are likely
to stay below SCA criteria Friday into Saturday.

&&

.FIRE WEATHER...
Lowering humidity levels and increasing winds over the next few
afternoons could lead to fire weather concerns across our
region. The lack of rainfall during the past week has led to dry
fine fuels over the region, with fine fuel moisture already below
20 percent.

A few rain or snow showers are possible across the Poconos from
time to time this week. Aside from that, dry conditions on tap.
Although most of the area is above normal for precipitation
since March 1, it has been a week since the last significant
rainfall, and no significant rainfall is expected this week.

Min RH values this week will generally range from 25 to 35
percent, and stronger westerly flow occurs over the area as well
with winds generally 15 to 20 mph with gusts 25 to 30 mph.

The day of highest concern looks to be Thursday, where surface
dew points drop into the upper single digits to low teens. Min
RH values may be as low as 20 to 25 percent, and west to
northwest winds could gust as high as 30 to 35 mph. By then, it
will be almost 2 weeks since the last significant rainfall.

Depending on how fast and how efficiently fine fuels dry out
further will add to possible concerns for the rapid spread of
any fires that may develop.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ430-431-
     450>455.

&&

$$

SYNOPSIS...Johnson
NEAR TERM...RCM/Staarmann
SHORT TERM...Johnson/Staarmann
LONG TERM...Johnson
AVIATION...Johnson/RCM/Staarmann
MARINE...Johnson/RCM
FIRE WEATHER...


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