Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 220130
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
930 PM EDT Thu Mar 21 2024

.SYNOPSIS...
High pressure continues to build overhead tonight. An area of low
pressure lifts north from the Gulf Coast and cold front approaches
from the Ohio River Valley on Friday. Drier conditions are
expected behind the frontal passage Sunday with high pressure
briefly building over the area Monday. Another front looks to
impact the area by the middle of next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
Winds, including transport winds, diminish overnight and RHs
recover into the upper 40s and low 50s. Temperature wise, lows
are expected to drop into the 20s for most tonight (low 30s
towards the waters). The combination of mostly clear skies and
light winds should help set up a good radiational cooling event
overnight, so some areas may even get into the low to mid 20s.

Additionally, there are several ongoing fires along the
Shenandoah Valley into eastern West Virginia. This, paired with
light winds, will cause some smoke issues in the mountain
valleys overnight into Friday morning. Have added some mention
of patchy smoke into the forecast along the Shenandoah Valley
tonight to account for that.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
Friday starts out dry before high pressure moves offshore and low
pressure approaches from the south while a frontal system approaches
from the west. As these two features move through, a mostly beneficial
rain, especially considering recent fire weather conditions, moves
into the region late Friday into early Saturday morning and continues
through Saturday evening.

The steadiest/heaviest rainfall looks to be along and east of
the Blue Ridge where 1 to 2 inches of rain can be expected.
Locally higher amounts are possible along and east of the I-95
corridor and along the eastern facing slopes of the Blue Ridge
where the upslope component will come into play. Areas further
west of the Blue Ridge will see rainfall amounts on the order of
a 0.5 to 1 inch. Lower totals may be found west of I-81 given
where the potential deformation axis sets up on the northern
fringe of the coastal low passing to our south.

The timing of steadiest rain for our has trended a bit later in
recent runs, focused more between 12z-18z. Given the recent dry
stretch of weather and a lack of a convective element flooding
does not appear to be a major concern at this time, but isolated
instances of flooding are possible late Friday night through
Saturday afternoon, especially in urban and poor drainage areas,
and on small streams. A Flood Watch is in effect where the
potential for flooding is highest.

With a cool air wedge in place and increasing southeasterly flow
Friday expect highs in the upper 40s to mid 50s. Slightly warmer
conditions can be expected along and west of the Allegheny Front
due to downsloping. Lows Friday night will fall back into the
low to mid 40s.

Coastal low pressure will continue off the SC/NC coast Saturday
afternoon and evening with the upper trough/cold front set to push
offshore Saturday night into Sunday morning. This will result in
decreasing rain chances from west to east across the area along with
cooling temperatures and increasing winds. Highs Saturday will push
into the low to upper 50s with south to southeasterly winds
gusting 15 to 25 mph. Lows Saturday night will fall into upper
20s to mid 30s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Sunday and Monday high pressure noses down over the Eastern US from
Canada with near normal temps for this time of year. Winds will
still be gusty Sunday, especially east of the Blue Ridge east over
the Bay. That due to the gradient between the departing low from
Saturday and the encroaching high.

Next up is mid week. A low moving northeast across Canada will swing
a cold front with its associated moisture over the Eastern US. There
likely will be a low developing on that front, but models vary
widely on where that might be. So at this point, it is just a chance
of rain that moves into the forecast Tue through Thu.

No wide swings in temps expected Sun thru Thu, with highs generally
in the 50s across the forecast area through that period.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
VFR conditions are expected through early Friday as high pressure
builds over the region. Winds have diminished this evening and
will remain light overnight as high pressure moves overhead.

Sub-VFR conditions return Friday evening as an area of low
pressure approaches from the Gulf Coast states. Timing of precip
onset has trended a bit later, with light rain approaching the
southern terminals (i.e KCHO/KSHD) Friday evening before
spreading northward toward the corridor early Saturday morning.
Light southeasterly winds will start the day Friday before
increasing late in the afternoon and evening hours. Speeds will
remain between 5 to 15 kts with gusts up to 25 kts especially in
the evening and diminish briefly overnight before low pressure
lifts north from the southern Appalachians toward the NC/SC
coast.

Sub-VFR conditions are likely at all terminals through the day
Saturday as rain and gusty winds impact the area. North/northwest
winds will likely gust 20-30kts knots Saturday afternoon into
Saturday night especially across terminals east of the Blue
Ridge. Precipitation exits the area from west to east Saturday
night into Sunday with gusty northerly winds lingering.

Gusty north winds expected Sunday, but VFR expected Sunday through
at least Tuesday morning...possibly thru Thursday depending on
development and placement of a possible low pressure system along
the cold front. That said, in some of the wetter solutions with Mid
Atlantic low, IFR is certainly possible midweek.

&&

.MARINE...
Winds have largely tapered off across the waters to below SCA
criteria. This will continue through at least Friday morning,
with winds picking up again on Friday afternoon ahead of the
next system.

Rain chances and another round of SCA winds return to the waters
Friday evening into Saturday afternoon as an area of low pressure
approaches from the south. The confidence for gale conditions
continues to increase for middle and southern portions of the
bay/tidal Potomac Saturday evening into Sunday due in part to a
very tight gradient overhead and Gale Watches have been issued.

Gales could continue into early Sunday before diminishing
slightly. Small Craft Advisories are possible after that through
the weekend.

&&

.FIRE WEATHER...
Winds will become much lighter overnight, being largely
terrain-driven in nature. The inversion will keep smoke pretty
thick in valley near ongoing fires tonight given the light
winds. The inversion should break by mid-morning, allowing for
smoke to lift up out of the valley a bit.

For Friday, higher humidity should help things out a bit, but
still looking at minimum RH values around 35-45 percent for
most. Winds will be gusty out of the south-southeast Friday
afternoon at 8 to 12 mph, gusting up to 18 mph. On the ridges
though, you can expecting 12 to 18 mph winds, gusting up to 25
mph at times.

The next chance for widespread wetting rain arrives Friday evening
into Saturday. Rainfall amounts of 1 to 2 inches can be expected
east of the Blue Ridge with 0.5-1 inch in areas further west.

Sunday and Monday look like mild days with relatively low wind
speeds.

.TIDES/COASTAL FLOODING...
Increasing onshore flow ahead of approaching low pressure will cause
an increase in tide levels Friday night into Saturday. Minor tidal
flooding is possible during this time, especially for typically more
vulnerable shoreline locales.

In the wake of low pressure, strengthening northerly flow will cause
a decline in water levels Saturday night through Sunday.

&&

.TIDES/COASTAL FLOODING...
Increasing onshore flow ahead of approaching low pressure will cause
an increase in tide levels Friday night into Saturday. Minor tidal
flooding is possible during this time, especially for typically more
vulnerable shoreline locales.

In the wake of low pressure, strengthening northerly flow will cause
a decline in water levels Saturday night through Sunday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flood Watch from late Friday night through Saturday afternoon
     for DCZ001.
MD...Flood Watch from late Friday night through Saturday afternoon
     for MDZ008-011-013-014-504-506-508.
VA...Flood Watch from late Friday night through Saturday afternoon
     for VAZ053-054.
WV...None.
MARINE...Gale Watch from Saturday evening through Sunday morning for
     ANZ530>532-535-536-538>540.
     Gale Watch from Saturday morning through Sunday morning for
     ANZ533-534-537-541>543.

&&

$$

SYNOPSIS...EST
NEAR TERM...CJL/CAS
SHORT TERM...CAS
LONG TERM...CS
AVIATION...CS/CAS
MARINE...CS/CAS
FIRE WEATHER...CJL/CAS
TIDES/COASTAL FLOODING...DHOF


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