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940
FXUS61 KLWX 180807
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
407 AM EDT Wed Sep 18 2024

.SYNOPSIS...
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Low pressure over the southern Appalachians will weaken today.
Meanwhile, another low will develop off the coast by tonight and
only slowly drift eastward through the weekend. A backdoor cold
front may push into the area Saturday. Strong high pressure
will build northeast of the area early next week while a low
pressure system approaches the Great Lakes.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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Vertically stacked low pressure is located over the southern
Appalachians this morning. Meanwhile, another low is beginning
to form east of Hampton Roads and will become the dominant low
by tonight. An easterly low level jet and some elevated
instability are supporting moderate to briefly heavy showers
moving across the area...even a few thunderstorms across central
Virginia. The prevailing idea is that showers and isolated
thunderstorms will be most widespread through midday. After
that, the low level jet weakens and the deeper moisture begins
to contract into the developing offshore low. However, models
have a wide range of solutions as to how the next 24 hours will
play out in terms of rain coverage. Efficient rain rates will
have to be monitored (some amounts in excess of an inch since
midnight southwest of Charlottesville), and some CAMs do show
some localized heavy/multi-inch rain totals. So far, heavier
elements have been transient, and combined with recent dry
conditions, any flood threat appears to be isolated at most.
Clouds will mute high temperatures today, with most areas rising
into the lower to mid 70s.

Tonight should have generally decreasing rain chances as the
offshore low results in some modestly drier air moving in from
the north. However, with the upper low nearly overhead, some
isolated to scattered showers may continue. Fog may develop if
breaks can occur in the clouds, which seems most plausible
across western parts of the area. Lows will be in the mid 50s to
mid 60s.
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&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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The upper level and surface lows are forecast to gradually drift
east or northeast Thursday and Friday, but there is still some
notable spread amongst guidance in their positioning. While the
upper low will still be close by Thursday and a few showers or
even a thunderstorm could pop up almost anywhere, the highest
chances appear to be closer to the Chesapeake (closer to the
surface low) and across the Appalachians (as a disturbance
rotates through the west side of the gyre). Some clearing could
occur if the low pulls away fast enough. Temperatures will
respond into the mid 70s to near 80.

The current forecast consensus has surface high pressure
settling over the area Friday and Friday night as the upper
trough/closed low moves to the east. This would result in dry
conditions and more sunshine, with temperatures rising into the
upper 70s to lower 80s. However, there is still some chance
(such as in the 00Z NAM) that they low remains closer to the
coast, which could result in more clouds and a chance of
showers. Have slight chance PoPs and more cloud cover along the
immediate Chesapeake for this forecast package.
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&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
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A backdoor cold front will move through the region Saturday. Cooler
and drier air will move in from the northwest and north Saturday and
Sunday. High temperatures will be below average both days.

High pressure building southeast behind the backdoor cold front will
keep conditions dry for the majority of our western and central
zones on Monday as well. There will be a low pressure system off of
the eastern seaboard that will have some energy filling around the
backside of it on Monday. Therefore, there is a slight chance for
showers in our eastern zones and could primarily be over the
Maryland eastern shore. High temperatures on Monday will be below
average too with highs in the lower to middle 70s. Higher elevations
stay cooler.

Later on Monday and into the day on Tuesday, a low pressure system
will approach our region from the west. This low could bring rain
chances to our western zones Monday evening through Tuesday. Highs
Tuesday could be milder with highs in the upper 70s as a return flow
develops ahead of the low pressure arriving from the west.
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&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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MVFR to IFR ceilings continue to overspread the area this
morning. All terminals should see a period of IFR conditions
through mid to late morning, with LIFT possible at CHO. Showers,
some moderate to briefly heavy, may also reduce visibility at
times, but the heaviest elements seem to be transient.

Showers should become more spotty in nature this afternoon as
developing off the coast starts to turn winds more northerly and
bring in some drying air. This also seems like it will raise
ceilings to VFR by late afternoon except at CHO. Those northeast
winds may gust close to 20 kt at times today.

MVFR to IFR conditions may redevelop late tonight, although
there is some uncertainty in whether this would be in the form
of low clouds or fog and the location of the restrictions.

A few showers may continue Thursday but overall there should be
a drying trend into Friday. There is some potential of low
clouds and/or fog developing both Thursday night and Friday
night however.

VFR conditions Saturday through Sunday night. Winds northerly 5 to
10 knots Saturday, becoming predominantly northeast 5 to 10 knots
Saturday night through Sunday night.
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&&

.MARINE...
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Small Craft Advisory conditions will continue in northeast flow
today as low pressure develops offshore. An isolated
thunderstorm can`t be ruled out amongst showers today. Winds
should gradually decrease tonight as the low starts to drift
away from the area. Advisory conditions may linger along the bay
into Thursday though depending on the position and strength of
the low. It does appear winds should be relatively lighter
Thursday night into Friday, but may strengthen again Friday
night amongst a tightening pressure gradient.

Small craft advisories possible Saturday and again Sunday afternoon
and evening as northeasterly winds kick up a little over the open
waters of the Tidal Potomac and central and southern Chesapeake Bay.
Winds northeast 10 to 15 knots gusts up to 20 knots both
periods.
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&&

.TIDES/COASTAL FLOODING...
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Anomalies remain highest this morning along the Potomac River.
Several advisories have been issued through this afternoon`s
high tide cycle. As low pressure turns winds more northerly
tonight, there may be a brief decrease in tidal levels. However,
as the low strengthens offshore, surge guidance shows increasing
water levels by Thursday evening into the weekend. Combined with
high astronomical tide levels, additional coastal flooding can
be expected. Some guidance suggests Annapolis and DC SW
Waterfront could even approach moderate flood levels.
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&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory from 7 AM this morning to 11 PM EDT
     this evening for DCZ001.
MD...Small Craft Advisory until 9 PM EDT this evening for MDZ008.
     Coastal Flood Advisory until 7 AM EDT this morning for MDZ014.
     Coastal Flood Advisory until 6 PM EDT this evening for MDZ016.
VA...Coastal Flood Advisory until 6 PM EDT this evening for VAZ057.
WV...None.
MARINE...Small Craft Advisory until 9 PM EDT this evening for ANZ530-
     538-539-542.
     Small Craft Advisory until 6 AM EDT Thursday for ANZ531>534-
     537-540-541-543.
     Small Craft Advisory until noon EDT today for ANZ535.
     Small Craft Advisory until 6 PM EDT this evening for ANZ536.
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&&

$$

SYNOPSIS...ADS
NEAR TERM...ADS
SHORT TERM...ADS
LONG TERM...KLW
AVIATION...ADS/KLW
MARINE...ADS/KLW
TIDES/COASTAL FLOODING...ADS