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216
FXUS61 KLWX 191851
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
251 PM EDT Thu Sep 19 2024

.SYNOPSIS...
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Low pressure will continue to drift off the Mid-Atlantic coast
through Friday with strengthening high pressure building north of
the region. A weak backdoor front may impact the area Saturday into
Sunday bringing an additional round of showers and thunderstorms. A
strong front and area of low pressure over the Great Lakes and Upper
Midwest look to push into the area by the early and middle part of
next week. Temperatures will remain at or slightly above normal
through Sunday.
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&&

.NEAR TERM /THROUGH FRIDAY/...
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Upper level low pressure continues to fill over eastern North
Carolina this afternoon with dominant low pressure spinning off
the coastal Delmarva. Plenty of moisture remains though along
with weak pieces of shortwave energy pivoting though. KIAD and
KRNK 12Z soundings from earlier this morning depict this
residual moisture with PWATS generally running between 1.4 to
1.7 inches.

Meanwhile, upper level low pressure will continue to deepen off the
coast of New England acting as a steering mechanism to push the
remnant trough axis eastward out of our region. With the trough axis
shunted east deep layer northerly flow will ensue allowing
drier air to advect into the area. Current GeoColor imagery (as
of 230pm) depicts this with breaks in the clouds across
northern Virginia, the eastern WV Panhandle, and much of MD.
Further east clear skies have been noted per observations and
cameras across northeast MD/MD Eastern Shore. These breaks in
the clouds are likely to continue through the afternoon
allowing high temperatures to push into the mid to upper 70s and
low 80s areawide outside of the mountains.

With the added sunshine, will come added instability which several
of 12z CAMs are picking up on for the remainder of the afternoon and
into the early evening hours. This is in association with a
disturbance rotating through the backside of the trough that will
allow for some scattered shower and thunderstorm activity mainly
across the WV/VA Highlands and southern Shenandaoh Valley later this
afternoon. Activity is currently ongoing in these aforementioned
areas feeding off of 500-1000 j/kg MLCAPE and bulk effective shear
less than 15 kts. No severe weather is expected with more beneficial
rainfall expected over drought stricken areas. Thunderstorm
activity should be pulse in nature and somewhat progressive
limiting widespread flooding concerns. Given the limited shear
and some training over the terrain one or two localized
instances of flash flooding cannot be ruled out.

Breaks in the clouds this afternoon will give way to additional
clearing overnight especially in areas along and west of US-15.
Patchy fog will be possible in some of the rural valleys. Lows will
range from the mid 50s to mid 60s.

The dry trend continues for Friday as low pressure pushes further
offshore. An isolated shower or thunderstorm cannot be ruled
out along the Blue ridge and back across the WV/VA Highlands
given added instability and weak convergence. Highs will reach
the lower to mid 80s for most areas. Friday night`s lows will
fall into the mid 50s to mid 60s again, with patchy valley fog
possible.
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&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
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There is better agreement amongst the guidance in regards to a
backdoor cold front which looks to pass through the region late
Saturday into Sunday. Upper level low pressure will continue to push
further off the New England coast Saturday allowing for a slightly
flatter upper level flow pattern overhead. Meanwhile, strong
Canadian high pressure will remain blocked to the north as a result
ultimately slowing the timing of the backdoor cold front into late
Saturday afternoon and Saturday night. The boundary appears to be
fairly weak with shortwave energy diving down through northwest
flow. This will promote scattered shower and thunderstorm
development especially in areas along and west of of I-95. The 12Z
ECMWF, GEM, and GFS all show this in some fashion during the 18z/2pm
Saturday-06z/2am Sunday timeframe. Capped PoPs at 30-40 percent
(highest along the Appalachians) for now until there is better
agreement from the ensemble data. Highs Saturday should now
remain in the lower 80s while lows remain close to a persistence
forecast.
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&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
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Ridging will build over the region during the early part of
next week, sliding offshore by Tuesday. A shortwave-trough will
move across the eastern Great Lakes and northern mid-ATLC
Tuesday flattening the ridge and increasing the risk of showers.
During the second half of next week, a deep upper low drops
into the area from the western Great Lakes and Midwest bringing
cooler and more unsettled weather conditions.
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&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
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Light northerly flow (5-10 kts) will advect drier air into the
region this afternoon leading to prevailing VFR conditions. Any
shower or thunderstorm activity should be confined to terminals
west of KCHO/KMRB between now-00z/8pm this evening. There is a
15 percent probability or less for VCTS at KCHO. For now opted
to to leave it out of this TAF cycle. Outside of the showers and
thunderstorms patch MVFR to IFR fog remains possible at
KMRB/KCHO late tonight into early Friday morning.

High pressure will maintain VFR conditions Friday, with patchy
fog possible Friday night at KMRB and KCHO. A backdoor cold
front and shortwave disturbance may bring some showers and
thunderstorms late Saturday afternoon and evening. Confidence in
this has increased amongst the latest deterministic guidance
although the confidence in coverage and intensity still remains
low.

No significant weather is expected to impact aviation Sunday into
Monday. Northeasterly winds on Saturday shift to easterly Sunday
afternoon, gusting 5 to 10 knots each day. Winds increase slightly
on Sunday in the eastern portions of the forecast area with KIAD,
KDCA, KBWI, and KMTN gusting 10 to 15 knots in the afternoon. Sub-
VFR conditions return beyond this point as another front pushes
in to the region.
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&&

.MARINE...
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Upper level low pressure will remain off the coast through the
weekend as high pressure builds north of the region. Light
northerly winds are expected this afternoon turning toward the
east and northeast Friday into Saturday. A backdoor cold front
looks to cross the waters Saturday afternoon into early Sunday
morning bring renewed potential for a brief period of Small
Craft Advisory conditions. Some marginal gusts up to 20 kts
can`t be totally ruled out mainly over the middle and open
waters of the bay Saturday evening into Saturday night.

SCA conditions are possible Sunday afternoon into Monday. Winds
northeast 10 to 15 knots gusts up to 20 kts late Sunday into Sunday
evening, mainly over the main stem Chesapeake and Tidal Potomac.
Winds becoming east then southeast 10 knots late Sunday night into
Monday and Monday night.
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&&

.TIDES/COASTAL FLOODING...
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Anomalies remain highest along the tidal Potomac River and lower bay
this afternoon. Several advisories remain in effect through this
evening`s high tide.

After remaining stable through tonight, water levels are forecast to
rise into the weekend as offshore low pressure traps water in the
Chesapeake. Combined with high astronomical tide levels, additional,
and more widespread, coastal flooding can be expected. Some guidance
suggests Annapolis and DC SW Waterfront could even approach moderate
flood levels. Coastal flood issues look to persist into next week.A
Coastal FLood Watch is in effect for Annapolis and the Anne Arundel
County Shoreline late Saturday evening through Saturday night.
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&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until midnight EDT tonight for DCZ001.
MD...Coastal Flood Advisory until 10 PM EDT this evening for MDZ014.
     Coastal Flood Advisory until 7 PM EDT this evening for MDZ016.
VA...Coastal Flood Advisory until midnight EDT tonight for VAZ054.
     Coastal Flood Advisory until 7 PM EDT this evening for VAZ057.
WV...None.
MARINE...None.

&&

$$

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