090
FXUS61 KLWX 180018
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
818 PM EDT Tue Sep 17 2024

.SYNOPSIS...
Low pressure over the Carolinas will gradually weaken through
Wednesday. Another low may develop off the coast during the second
half of the week. A backdoor cold front may push into the area
Saturday. Strong high pressure will build northeast of the area
in its wake.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Low pressure over west-central North Carolina will continue to
move toward the northwest tonight. Low clouds will continue to
cover the forecast area, especially south of I-70. Waves of
light to at times moderate rain will continue to inch further
north through the night.

PWATs were in excess of 1.75 inches south of I-66/US-50 and east
of the Blue Ridge Mountains as of early this evening, with PWATs
of 1.90-2.00 inches advecting in from the southeast. Guidance
remains split on the strength of a low-level jet tonight, and
thus how far northwest these higher PWAT values get. Waves of
rain will continue for much of the area regardless, but the
intensity varies among the latest model runs. The NAM12/NAMNest
and ECMWF, for example, have an area of heavier rainfall totals
from far northern VA into central and northeast MD (including
the greater Baltimore/Washington metro areas - generally 1-3").
However, recent RAP/HRRR runs are much less enthused. Given the
antecedent dry conditions, no Flood Watch has been issued as any
flooding will be conditional and isolated wherever any heavier
rain bands set up over vulnerable (i.e. urban) basins. MUCAPE of
less than 500 J/kg should tend to keep rainfall rates modest
(less than a half inch per hour).

Lows tonight in the middle 50s in the west and the lower to
middle 60s in the eastern zones.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
The aforementioned low pressure will continue to move across
western NC and further west on Wednesday. Rain will continue
through most of the day for a large portion of the area, with
the VA Piedmont likely receiving the most precipitation.
Additional totals of 2-3" are certainly possible through the day
on Wednesday as the low begins to break down and a coastal low
forms off the Delmarva. Cannot rule out a rumble of thunder in
the afternoon hours but overall convective activity should be
fairly suppressed. Highs top out in the upper 60s to low 70s
along and west of the Blue Ridge where the more cooler side of
the low resides and a few degrees warmer further east towards
the waters. Overnight lows Wednesday night drop down into the
mid to upper 50s along the Allegheny Front and low 60s further
east.

As the coastal low begins to shift further northeast, expect
shower chances to decrease from west to east during the day on
Thursday. There may be some general clearing later in the day.
Highs will top out in the upper 70s to near 80 for most areas.
Northwesterly flow will allow temperatures to drop down into the
upper 40s to low 50s along portions of the Allegheny Front
Thursday night, with mid to upper 50s more common further east
with low 60s near the waters.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Long term period continues to trend drier as model guidance keeps
the trough axis offshore. A backdoor cold front is set to drop
through the forecast area Friday afternoon and throughout the day on
Saturday as an upper level trough deepens over Canada into New
England. Cooler and drier air will move in with temperatures
expected to stay below normal. High pressure will keep conditions
primarily dry with a low pressure system off the coast of the
Carolinas leading to slight chance of PoPs in the southeastern
portions of the area through Monday. Precipitation chances increase
elsewhere on Monday as a low pressure system approaches from the
west.

High temperatures will be in the upper 70s to low 80s on Friday with
higher elevations staying in the mid to low 70s. Temperatures cool
slightly each day with high temperatures on Monday expected to be in
the low to mid 70s for most. High elevations will stay in the upper
50s to 60s. Overnight low temperatures will be in the 50s for most
each night with metro areas staying in the low 60s.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
IFR CIGs were expanding out of the central VA Piedmont as of
00Z. These CIGs should expand to the DC area terminals through
06Z, then the Baltimore terminals and MRB by 09Z. Intermittent
IFR CIGs (or VSBY in any heavier rain) is possible prior to
that, with patchy LIFR possible heading into Wednesday morning.
Winds will remain out of the east 5-10 kts with occasional gusts
to around 15 kts.

Rain showers will likely continue off and on Wednesday with low
pressure nearby. Winds will be northeast to east 5 to 15 kts
through Wednesday. Gusts of 20 to 25 kts are possible, mainly
each afternoon and evening, especially at terminals close to the
waters and along the ridges. With the residual low pressure
nearby, expect periods of MVFR to IFR conditions.

Underneath a mid-level low pressure system on Thursday, scattered
showers may develop across the area. Clouds should be abundant
which may afford periods of sub-VFR conditions.

Prevailing VFR conditions are expected Friday and Saturday with dry
conditions at all terminals. Northeasterly winds on Friday shift to
easterly on Saturday.

&&

.MARINE...
SCA conditions will persist through the night, especially south
of the Chesapeake Bay Bridge on the Chesapeake Bay and below
Dahlgren on the tidal Potomac River. This is in association with
a tightened pressure gradient from blocking high pressure to
the north and low pressure moving inland across the coastal
Carolinas. As a weakening area of low pressure tracks through
the area, winds will be out of the east on Wednesday while
likely remaining at SCA levels for at least portions of the
waters. Winds will become more northeast Wednesday, then more
northerly while diminishing on Thursday.

Northeasterly winds are expected to stay below SCA criteria on
Friday with winds gusting 10 to 15 knots. Winds shift more easterly
on Saturday with Small Craft Advisories likely as winds gust 15 to
20 knots.

&&

.TIDES/COASTAL FLOODING...
With low pressure inland over the Carolinas and winds from a
northeasterly direction, there have not been significant rises
in anomalies, with the highest values greater than one foot
along the tidal Potomac River. Advisories remain in effect, but
most flooding will be marginal. Between the full moon and
continued onshore flow, tide levels will likely remain elevated
and near minor flood thresholds much of the week.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 10 PM EDT this evening for DCZ001.
MD...Small Craft Advisory until 9 PM EDT Wednesday for MDZ008.
VA...Coastal Flood Advisory until 10 PM EDT this evening for VAZ054.
WV...None.
MARINE...Small Craft Advisory until 9 PM EDT Wednesday for ANZ530>534-
     537>543.
     Small Craft Advisory until noon EDT Wednesday for ANZ535.
     Small Craft Advisory until 6 PM EDT Wednesday for ANZ536.

&&

$$

SYNOPSIS...ADS/DHOF/ADM
NEAR TERM...KLW/DHOF/ADM
SHORT TERM...KLW/DHOF/ADM
LONG TERM...AVS
AVIATION...AVS/DHOF/ADM
MARINE...AVS/DHOF/ADM
TIDES/COASTAL FLOODING...LWX