387
FXUS61 KLWX 160734
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
334 AM EDT Thu May 16 2024

.SYNOPSIS...
Drier conditions are expected today through Friday as low pressure
slowly pushes off the Mid-Atlantic coast and weak high pressure
builds in. Increased shower and thunderstorm chances return this
weekend as another low pressure system pushes across the region.
High pressure briefly returns Monday and Tuesday ahead of a slow
moving cold front set to cross by the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A brief reprieve in the active weather pattern over the last few
days as weak mid-level ridging builds into the region and low
pressure pushes further off the Mid-Atlantic coast. Pockets of
clearing have been noted this morning on satellite imagery as low
pressure off the NJ coast fills in and surface low pressure to the
south pushes off the VA/NC coast. With the clearing comes areas of
dense fog given residual moisture trapped in the low levels and
drier air filtering in aloft. Any fog will be relegated to areas
west of the Blue Ridge and close to the waters given this is where a
few light showers and areas of drizzle passed through during the
early part of the overnight period.

With mid-level ridging/weak high pressure set to take over this
afternoon and evening additional clearing will ensue. A mix of sun
and clouds can be expected for most locations due in part to
downsloping north to northwest flow around departing low pressure
offshore. 00z model soundings do indicate some high based strato-
cumulus across the area this afternoon and evening with perhaps a
spotty shower or isolated thunderstorm tied to the mountains during
the peak heating period. Added sunshine today and subtle downslope
flow should boost temperatures into the mid to upper 70s across much
of the region. Mountain locations and those adjacent to the bay will
see highs in the upper 60s and low 70s.

Dry conditions will continue tonight with weak mid level ridging
sitting to the south of the region. Skies will remain partly cloudy
with areas of patchy fog especially in river and mountain valley
locations. Lows tonight will fall back into the mid to upper
50s.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
By Friday, clouds will be on the increase once again as low
pressure approaches from the Ohio River Valley. The day will
likely start off dry with weak mid-level ridging/high pressure
sitting across the southeast U.S. The brief reprieve in active
weather won`t last long as a warm front lifts in from the south
and west Friday afternoon/evening. South to southwesterly flow
will ensue as a result allowing ample moisture advection to push
north ahead of the approaching upper level low pressure system
from the Ohio River Valley Saturday.

Skies will likely remain partly to mostly cloudy before becoming
overcast Friday evening and night. The warm front combined with
modest surface heating and increasing dewpoints (upper 50s and low
60s) should allow for enough of a spark for widely scattered
thunderstorms Friday afternoon/evening especially west of the Blue
Ridge. The severe weather threat appears to be low given limited
shear and CAPE. Isolated instances of flooding could be possible due
to the slow movement of thunderstorm activity (i.e
pulse/multicellular modes). High temperatures Friday will be in the
mid to upper 70s. Moisture increases by Friday night with increased
rain chances and lows dipping down into the mid to upper 50s.

It`s a soggy start to the weekend as an upper level trough/slow
moving low pressure system push across the central Appalachians and
toward the VA/NC coast. Expect fairly widespread shower and
thunderstorm activity Saturday with decreasing coverage as the low
pushes east toward the coast late Saturday night into Sunday. Severe
weather does not appear to be a concern at this point given limited
CAPE and shear with ample cloud cover overhead. Localized flooding
could be the bigger concern given repetitive rounds of rain and rich
moisture (high PWATS around the the percentile) funneling in. For
those with plans outdoors Saturday appears to be the wettest
compared to Sunday even though models continue to stall the low
offshore. High temperatures will struggle to get out of the mid to
upper 60s (low 60s across the PA/MD line and mountains) Saturday
afternoon. Lows Saturday night will fall back into the mid to upper
50s.


&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
A split flow regime persists across the country to finish out the
weekend. For Sunday, a slow moving upper trough will pass by to the
south across the Carolinas. Given the close proximity of the frontal
system to the local area, some rain chances will loom for at least
the first half of the day. This is particularly the case for those
south of I-66/U.S. 50. With the Mid-Atlantic region in a modified
cold-air damming wedge, temperatures remain seasonably cool thanks
to northeasterly onshore winds. The latest forecast package calls
for mainly 60s on Sunday which is nearly 10 degrees below average
for mid-May. Any rain chances wane by later in the day as the
frontal system slowly exits the Carolina coast.

Expect a dry start to the work week as northern stream ridging sets
up over the northeastern U.S. through Tuesday. Depending on model
solution, some shower activity could return to areas west of I-95 by
late Tuesday. Temperatures are able to rebound owing to the building
heights aloft coupled with a greater amount of sunshine. Return flow
does not really kick in until mid-week which should hold down
humidity levels. By Wednesday, daily highs return to the 80 degree
mark, accompanied by prevailing southerly winds. This ushers dew
points into the low/mid 60s which will make conditions feel a bit
more humid. Additionally, global ensembles show a large uptick in
instability profiles. Ultimately this will bring a better chance for
diurnal convection, particularly in advance of a cold front tracking
through late Wednesday. Despite the frontal passage, temperatures
are not expected to drop much, but a decrease in humidity levels is
more likely for later in the week.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
Skies continue to clear this morning allowing for areas of dense fog
to sprout up between western and southern terminals (i.e KCHO, KMRB,
KHGR, KSHD, KCJR, and KFDK). GOES Nighttime Microphysics RGB
continues to show the bulk of fog across the Potomac Highlands,
Shenandoah Valley, and Virginia Piedmont with visibility values
bouncing between a 1/4 to 2 miles. Within the corridor itself mid
and high level clouds remain prevalent leading to less fog
formation. Even here, patchy and locally dense fog is likely through
daybreak (at least 14z/10am) due in part to ample moisture trapped
within the low levels.

Vsbys will improve beyond 14z/10am with ceilings likely to scatter
out in many locations later this morning and into the afternoon as
downsloping north to northwest flow pushes drier air into the
region. Expect strato-cumulus to dot the skies at all terminals this
afternoon and evening with cigs running between 050-090 feet. A
spotty shower or t-storm cannot be ruled out during the peak heating
period at terminals west of KMRB. Winds will turn to the north and
northwest today at 5-15 kts with gusts up to 25 kts at times. This
is due in part to the gradient between low pressure offshore and
weak high pressure building in at the surface.

Low ceilings and/or fog may redevelop tonight into Friday morning
especially at valley terminals (i.e KMRB, KSHD, KHGR, and KCHO).
Confidence is slightly lower on fog formation given weak mid level
ridging aloft and drier air filtering south on north to northwest
flow.

Flight conditions will slowly deteriorate Friday afternoon into
Friday evening especially at terminals west of the corridor. This is
due to increased shower and thunderstorm coverage as a warm front
lifts into the area. Low cigs and vsbys will continue into Friday
night and Saturday as widespread shower and thunderstorm activity
associated with an upper level low pressure system pivots across the
terminals.

Given northeasterly onshore flow within the cold-air damming wedge,
low ceilings are a possibility on Sunday. Thus, sub-VFR conditions
are possible along with some shower activity. Given little change in
wind direction, these lower ceilings could persist into Monday
morning. Otherwise, conditions trend drier through the rest of
Monday with mostly sunny skies and VFR conditions expected.


&&

.MARINE...
SCA conditions are expected for all waters today with a tightened
gradient across the region. North to northeasterly gusts up to 25
kts are possible through late afternoon with winds gradually
diminishing this evening and into the overnight hours. Lighter winds
are expected Friday into Friday night with weak high pressure
sitting south of the waters.

SCA conditions return Saturday under increased onshore east to
northeast flow. Low pressure will pass south of the waters Saturday
night into Sunday leading to a continuation of SCA conditions. This
will be especially true over middle and lower portions of the bay
and lower tidal Potomac where a bit more channeling could occur.
Numerous showers and perhaps a few thunderstorms will accompany this
system through Saturday into early Sunday. Winds Saturday night into
Sunday will gradually shift to north-northeasterly as the low slides
across the region.

Prolonged northeasterly onshore flow will bring near 20 knot gusts
to portions of the waters. Therefore, Small Craft Advisories may be
needed on Sunday, perhaps lingering into Sunday night. Given high
pressure along coastal New England and low pressure off the
Carolinas, additional northeasterly winds could approach advisory
levels even into Monday.


&&

.TIDES/COASTAL FLOODING...
Waters levels will gradually decrease today with north to
northeast flow behind departing low pressure.

Tidal anomalies will begin to rise again Friday and into the weekend
given a fairly prolonged period of east to southeasterly onshore
flow. A number of sites will return to Action stage, with the more
sensitive locations pushing into Minor. Elevated water levels likely
persist into Monday given little change in the overall wind
direction.


&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 PM EDT this evening for
     ANZ530>534-537-539>541-543.
     Small Craft Advisory from 8 AM this morning to 6 PM EDT this
     evening for ANZ535-536-538-542.

&&

$$

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