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720
FXUS61 KLWX 191421
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1021 AM 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 TONIGHT/...
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Upper level low pressure continues to fill over central and eastern
North Carolina this morning with dominant low pressure spinning
off the coastal Delmarva. Plenty of moisture remains though
along with weak pieces of shortwave energy pivoting though. This
has led to a few isolated showers here and there this morning
with coverage expected to continue to decrease into early
afternoon. KIAD and KRNK 00Z soundings also depict this 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 1015am) depicts this with breaks in the across northern
Virginia and central 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 later this 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. No
severe weather is expected with more beneficial rainfall expected
over drought stricken area. Thunderstorm activity should be
pulsey in nature and somewhat progressive limiting any
widespread flooding concerns.

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.
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&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Guidance has converged on a solution keeping the low far enough
away that Friday should be a dry day with partly cloudy skies.
One exception is the southwestern corner of the forecast area
where weak convergence and instability may again result in a few
showers or a thunderstorm. 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.

The forecast for Saturday appears to be in flux. With the low a
bit farther offshore and a slightly flatter upper level pattern
overhead, the strong Canadian high may be blocked to the north
and the previously advertised backdoor cold front associated
with it may not arrive until Sunday. However, there is potential
for a shortwave to move into the area in northwest flow which
could bring some showers and thunderstorms. The 00Z ECMWF, GEM,
and GFS all show this in some fashion. Capped PoPs at 20-30
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.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Cooler and drier air will move into the region on the northeast
flank of the backdoor cold front on Sunday. High temperatures will
be a couple of degrees cooler than average with highs in the middle
70s for most.

High pressure will build in from the northeast on Monday, while a
ridge of high pressure in the middle and upper levels sneak
into the region from the west during the same time. This
combination will keep most of our region dry and cool. A
lingering or perhaps dissipating backdoor cold front against the
Appalachians will be the focal zone for any developing showers
in the mountains and perhaps a few sneaking into the Shenandoah
Valley later Monday. High temperatures will be in the lower to
middle 70s.

The ridge of high pressure slowly flattens Tuesday into Wednesday as
waves of energy are expected to move into our region. A chance of
showers will accompany this energy and could venture as far as the I-
95 corridor on Tuesday. Temperatures will stay cool.

As for Wednesday, rain chances spread to the Chesapeake Bay with an
approaching cold front arriving sometime late Wednesday or Wednesday
night. The western half of our region stand the better chance of
showers and/or thunderstorms midweek into early Thursday.
Temperatures may be a few degrees warmer with a return flow ahead of
the front.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
Drier air moving in from the north has maintained VFR conditions
across northern areas. However, it does seem ceilings are
trending toward MVFR even at CHO -- where it may take until this
afternoon to reach persistent VFR conditions, with some
uncertainty in timing noted. Spotty light rain or drizzle could
occur through the morning and a brief period of fog could occur
around dawn for CHO, IAD, and MRB...although it seems like
chances for IFR or lower conditions are lowering.

For the remainder of the day VFR ceilings will persist but with
dry conditions and light north winds. A shower or thunderstorm could
approach CHO late this afternoon but confidence is low. For
tonight, fog is possible at MRB and CHO.

High pressure will maintain VFR conditions Friday, with fog
possible Friday night at MRB and CHO. A disturbance may bring
some showers and thunderstorms Saturday afternoon or evening,
but confidence as low as the forecast for this period has been
changing.

VFR conditions Sunday through Monday night. Winds northeast to east
5 to 10 knots Sunday and Sunday night. Winds becoming more
southeasterly 5 to 10 knots Monday and Monday night.

&&

.MARINE...
Winds have been lessening this morning. Low pressure will remain
off the coast through the weekend while high pressure builds
north of the area. So north winds will continue, perhaps
becoming northeast or east at times. Wind forecasts have trended
down a bit, especially for Saturday, so Small Craft Advisories
are looking less likely. However, some marginal gusts up to 20
kt can`t be totally ruled out along the bay.

Small craft advisories possible late Sunday afternoon and Sunday
evening. Otherwise, no marine hazards expected Sunday morning
nor late Sunday night through Monday night. 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.

&&

.TIDES/COASTAL FLOODING...
Anomalies remain highest along the tidal Potomac River. Several
advisories remain in effect through this evening`s high tide.
Have not extended the advisories yet since the following high
tide cycle looks to be marginal minor flooding at most. 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.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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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.
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&&

$$

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