763
FXUS61 KLWX 210759
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
359 AM EDT Thu Aug 21 2025

.SYNOPSIS...
A meandering frontal zone will continue to slide south of the
area today. Meanwhile, Hurricane Erin is expected to make its
closest approach to St. Mary`s County this morning. Erin will
move further offshore this evening with weak high pressure
building in for Friday into the first half of Saturday. Another
cold front will cross the area Monday morning before a strong
dome of high pressure approaches from the Midwest next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A frontal zone which continues to meander about the region has
finally begun to pull away toward the southeast. The early
morning surface analysis places this slow moving boundary across
southern Delaware back across central Virginia into southern
West Virginia. This has fostered a return of the onshore flow
regime which has ushered in another round of thick low stratus.
With gentle lift within the saturated boundary layer, some
drizzle and passing showers continue to drift toward the
southwest. Where precipitation is falling, some reduction in
visbility is evident in observational data. Expect this pattern
to hold strong through the morning hours with temperatures slow
to increase given the lack of solar insolation.

Further equatorward acceleration is expected through the day,
particularly as Hurricane Erin begins to pull further away from
the western Atlantic. Overall synoptic wind fields are likely to
expand given the interaction of the front/upper trough and
offshore tropical cyclone. Increasing pressure gradients will
encourage an uptick in north-northeasterly winds, particularly
along and east of I-95. Northerly gusts up to 20 to 25 mph are
likely, locally higher over the waters (see Marine section).
With some residual moisture and weak lift overhead, isolated to
widely scattered showers may pop up. Like this morning, any such
shower would track toward the southwest. A couple rumbles of
thunder are not out of the question around Highland and Augusta
counties given closer proximity to the front. Any convective
threats wind down by around 6 PM.

The temperature forecast has trended down given additional
clouds and northerly cold advection. Forecast highs will be in
the 70s with mainly 60s across the mountains. Relative to
mid/late August climatology, this forecast is around 8 to 12
degrees below average.

Overall wind fields will gradually weaken into night as the
boundary layer stabilizes. While areas east of U.S. 15 can
expect mostly clear skies, clouds likely linger off to the west.
Such cloud cover may offset more widespread fog development
overnight. Low temperatures are forecast to be in the upper
50s to mid 60s, with slightly cooler number in the mountains.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
With weak high pressure building into the area on Friday, expect
tranquil weather with mostly sunny skies. The pronounced
northerly flow will have a notable effect on moisture levels as
dew points fall into the mid 50s to low 60s on Friday.
Additionally, winds turn much lighter as the impacts from the
trough/tropical cyclone combination shift well offshore.
Forecast high temperatures should return to the upper 70s to low
80s (5 to 10 degrees cooler for mountain locales). The
combination of high pressure and a dry air mass will encourage
another cool night ahead. Friday night`s temperatures will
mainly be in the upper 50s to low 60s (mid 60s inside D.C. and
Baltimore). Areas that fully radiate could even see some spotty
mid 50s.

On Saturday, a formidable upper trough accelerating across
Ontario will spread ample height falls across the Great Lakes
into the Ohio Valley. While the most notable effects wait until
Sunday, the initial approach of this system will introduce
shower and thunderstorm chances for western locations. A return
southerly flow at the surface should increase low-level moisture
content. Some uptick in instability is likely given the
warm/moist advection regime. However, with the main forcing off
to the west, expect much of the convective action to focus back
toward the Alleghenies. Terrain circulations will likely be the
trigger before activity spreads downstream. At this point, storm
chances generally shut off just east of I-81.

The influence of upstream height falls start to kick in
overnight on Saturday. This supports increasing shower and
thunderstorm chances through the night across the entire area.
After a seasonably mild day, nighttime low temperatures fall
into the 60s (upper 50s for the mountain ridges).

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
A deep upper trough will dig over the Great Lakes on Sunday as low
pressure at the surface tracks toward Hudson Bay. Winds aloft will
start to increase as the upper trough approaches, atop what will
also be an unstable pre-frontal airmass. Showers and thunderstorms
appear likely Sunday afternoon ahead of the system`s approaching
cold front, and some of these storms could potentially be strong to
severe, given the overlap of instability and deep layer shear.
Temperatures will be seasonable, with highs in the upper 70s to mid
80s, but it will be quite humid, with dewpoints in the upper 60s and
lower 70s.

The vast majority of guidance has the system`s cold front moving
through prior to peak heating on Monday, with strong dry advection
ensuing in its wake. If the front clears the area, dry conditions
will ensue on Monday, but if the front were to progress slower off
toward the east, a shower or thunderstorms could be possible Monday
afternoon. The front will surely clear the area prior to Tuesday.
Mostly sunny, cooler, and much less humid conditions are expected
behind the front, with highs only in the 70s to near 80, and
dewpoints dropping into the 40s to near 50 for Tuesday and
Wednesday.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
While there was some reprieve from the prolonged low ceilings,
the main frontal zone has again moved south of the region. The
post-frontal northeasterly flow has led to another round of IFR
ceilings (spotty LIFR at times). Some reductions in visibility
from drizzle and passing showers also are noted. This pattern
holds through much of the morning hours with restrictions
continuing. A return just to MVFR conditions is not likely until
the early afternoon, with VFR by the early evening.

Additionally, the combination of this front/trough with
Hurricane Erin offshore will increase north-northeasterly
winds. Gusts up to 20 to 25 knots are possible today before
decreasing into the night. High pressure returns on Friday with
VFR conditions likely. Convective chances come back on Saturday,
but only for the western terminals. This come with southerly
winds gusting to around 10 to 15 knots. Some expansion in
showers is likely into the overnight hours.

Prevailing VFR conditions are expected on Sunday and Monday,
although brief drops to sub-VFR may be possible on Sunday as
thunderstorms move through. Winds will be out of the south on
Sunday, and then out of the west to northwest on Monday.

&&

.MARINE...
The meandering frontal zone has again shifted south of the area
early this morning. It will remain like that as the front slides
southeastward as a cold front. The combination of this
front/trough with the presence of Hurricane Erin offshore will
expand overall wind fields. A gusty north-northeasterly wind
overspreads the waters today with gusts around 20 to 25 knots
(25 to 30 knots over the southern waters). Small Craft
Advisories go into effect for all waters. Depending on how
gusty conditions get, occasional gale-force winds are certainly
possible late this morning into the afternoon. If brief in
nature, this uptick would be handled by a Marine Weather
Statement.

These winds remain slightly elevated into tonight and Friday
morning. Small Craft Advisories may get extended into Friday
morning across the more southern waters. Winds decrease for
the remainder of Friday as high pressure settles over the
waters. This ridge does weaken into Saturday as the next frontal
system approaches from the west. Southerly winds increase in
earnest with gusts to around 15 knots or so.

Sub-SCA level winds are expected on both Sunday and Monday. Winds
will be out of the south on Sunday, and then out of the west to
northwest on Monday. SMWs may potentially be needed as thunderstorms
pass over the waters Sunday afternoon into Sunday evening.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies will steadily rise for the next 12 to 24 hours
as onshore flow strengthens in response to Hurricane Erin
tracking southeast of the area.

As winds slacken Friday night into Saturday, a snap-back event
is expected to occur raising water levels further. Moderate
coastal flooding is likely at Annapolis and widespread minor
coastal flooding elsewhere. Water levels likely remain elevated
until the cold frontal passage that comes in early Monday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory until 3 AM EDT Friday for MDZ008.
     Coastal Flood Advisory until 8 AM EDT this morning for MDZ014.
     Coastal Flood Advisory until 3 AM EDT early this morning for
     MDZ016.
VA...Coastal Flood Advisory until 3 AM EDT early this morning for
     VAZ057.
WV...None.
MARINE...Small Craft Advisory until 3 AM EDT Friday for ANZ530>533-
     538>542.
     Small Craft Advisory until 6 AM EDT Friday for ANZ534-537-543.
     Small Craft Advisory from 9 AM this morning to 8 PM EDT this
     evening for ANZ535-536.

&&

$$

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