732
FXUS61 KLWX 162006
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
406 PM EDT Wed Jul 16 2025

.SYNOPSIS...
A cold front will move in from the north Thursday night. This
front will stall out on Friday and then oscillate back and
forth across the area through early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Current satellite imagery (as of 330 PM) shows scattered
thunderstorms starting to form along a prefrontal trough
located just to the east of the Alleghenies. Additional
thunderstorms are expected to form in this region over the
course of the afternoon as mid-level height falls attendant to a
shortwave approaching from the Ohio Valley move in. Activity
that forms within this pre-frontal trough is expected to grow
upscale and eventually move off toward the east later this
afternoon into this evening. However, questions remain regarding
just how far east this activity will make it.

Further west, a remnant MCV and blossoming thunderstorm activity
are evident on satellite across southern Ohio. This activity is
also expected to expand in coverage as it tracks eastward this
afternoon, potentially developing into a north-south line. Some
guidance suggests that these storms may reach the Allegheny
Front late this evening, before eventually decaying as they
track eastward toward I-81 during the first half of the
overnight hours.

Most guidance shows precipitable water values increasing to near
or in excess of two inches across the majority of the forecast
area later this afternoon as rich low level moisture is drawn
northward ahead of the aforementioned shortwave, while deeper
moisture in the mid-upper levels advects in from the Ohio Valley
atop the low-level moisture. The 12z IAD sounding shows a
precipitable water value of 2.04 inches, which is well above the
90th percentile for this time of year. The 12z ILN (Wilmington,
OH) sounding shows the much deeper saturation that will move
overhead later today. The 00z HREF mean has PWATs increasing to
in excess of 2.2 inches to the east of the Blue Ridge this
evening, which would challenge the daily record at the IAD
sounding site. GFS forecast precipitable water standardized
anomalies exceed 2 sigma across the bulk of the forecast area by
later this evening, which confirms that a highly anomalous
level of moisture will be present.

SPC Mesoanalysis currently shows 2000-3500 J/kg of MLCAPE across
the area. With such anomalous levels of moisture and ample
instability in place today, any thunderstorms will be capable of
producing very heavy rainfall rates. Guidance suggests that the
most intense storms may be capable of producing in excess of an
inch of rain in 15 minutes. Overall, rain rates should be
similar to what was observed on Monday. Flow in the 850-500 hPa
layer will increase to around 20-25 knots by later this
afternoon, which suggests that storms should have some decent
forward motion. However, with the low-level jet speed being
comparable to the mean steering flow, localized backbuilding may
be possible. With the potential for very heavy rainfall
producing, backbuilding storms there are flash flooding concerns
this afternoon into this evening. A Flood Watch for flash
flooding has been issued for much of the forecast area this
afternoon into this evening. The Watch is already in effect to
the west of the Blue Ridge, and starts at 5 PM further east.
Confidence in flash flooding occurring is the highest to the
west of the Blue Ridge, where large scale forcing for ascent and
resultant storm coverage should be highest. There also might be
slightly higher potential for backbuilding/training further
west before more robust cold pools get established. Further
east, there are some uncertainties regarding the coverage of
storms, and it`s possible that some locations in the watch don`t
receive any rain at all this evening. However, the background
environment is extremely favorable for producing heavy rainfall,
and any storm that does occur should produce extremely high
rainfall rates, which would cause issues in the Metro areas, if
it were to occur. Since the potentially is there for higher end
flash flooding, at least conditionally, the decision was made to
bring the watch all the way east through the Metros, even
thought the confidence isn`t the highest. In terms of timing,
storms are ongoing to the west of the Blue Ridge, and should
continue through the early evening hours. Further east, the main
impacts should be during the evening hours (roughly 6 PM-
Midnight for the Metros).

DCAPE is only around 500-600 J/kg, and low-level lapse rates
are only around 7-8 C/km, which could limit downdraft strength
and wind production a bit. The increasing winds in the 850-500
hPa layer could be a factor that would work in favor of wind
production. Some CAMs (notably the HRRR) show storms producing
strong winds this afternoon. SPC currently has most of the area
outlooked in a Marginal Risk for severe thunderstorms, driven
by damaging wind potential.

Outside of storms it will be another hot and humid day, with
highs in the upper 80s to lower 90s, and dewpoints holding in
the 70s. Storms should gradually wind down through the evening
hours, giving way to dry conditions during the second half of
the night.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Low pressure will track through the St. Lawrence Valley tomorrow
as a trailing cold front drops southward through the Eastern
Great Lakes. Flow aloft will stay zonal, with slight mid-level
height rises. A hot and humid airmass will remain in place at
the surface, but some drier air will start to build in aloft,
dropping precipitable water values back below two inches. The
hot and humid conditions at the surface will push us close to
Heat Advisory criteria, as temperatures climb into the low-mid
90s and dewpoints hold in the 70s. A Heat Advisory may need to
be considered for portions of the area at a later time. The
drier air aloft and lack of large scale forcing should lead to a
much lower coverage of storms tomorrow, but a few storms are
still expected to form on a prefrontal trough during the
afternoon and move eastward across the area. The drier air and
increasing flow aloft should also limit the potential for flash
flooding. Damaging winds may potentially become a greater
threat, as model soundings show much higher DCAPE values
(around 1000-1500 J/kg) and steeper low- level lapse rates
(closer to 8-9 C), both of which should enable storms to have
stronger cold pool driven downdrafts. We`re currently outlooked
in a Marginal Risk for severe thunderstorms by SPC, driven by
damaging wind potential. Any thunderstorms should quickly wind
down and progress off to our east during the evening hours,
leading to dry conditions overnight.

The system`s cold front will move southward across the area late
Thursday night, before eventually stalling out across the area
on Friday. Central Virginia to Southern Maryland will likely
remain on the warm/humid side of the boundary, and will have a
much greater chance for afternoon showers/thunderstorms than
locations further north during the day Friday. High temperatures
will range from the mid 80s across northern MD to the low 90s in
central VA and southern MD. Dewpoints will range from the mid
60s across northern MD to mid 70s across central VA.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
A warm front will lift north of the area Saturday while heights
aloft fall in advance of a cold front fcst to sweep through the area
Sunday night. Expect active thunderstorm days both Sat and Sun with
risk of some severe wx and isolated flash flooding.

After Monday, global models show subtropical ridge building over the
Mid-Atlantic leading to a hotter trend and a significant downward
trend in convection.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Earlier sub-VFR ceilings have improved back to VFR. Prevailing
VFR conditions are expected through the afternoon, but
thunderstorms may lead to temporary drops to sub-VFR conditions
at any of the terminals through this evening. VFR and dry
conditions are expected late tonight through tomorrow morning.
Winds today will be light out of the south to southwest.

Winds will pick up out of the west to southwest tomorrow, and
may gust to around 20 knots at times. Prevailing VFR conditions
are expected, but a brief thunderstorm can`t be ruled out
during the afternoon or evening hours. Areal coverage of the
storms should be much lower than today, so have just included a
PROB30 group for now. Additional thunderstorms appear possible
on Friday, especially in the vicinity of CHO.

Active thunderstorm days both Sat and Sunday with risk of some
severe.

&&

.MARINE...
Winds will gradually pick up out of the south this afternoon,
but should remain sub-SCA level in nature until after dark. SMWs
may be needed as thunderstorms move over the waters this
evening. SCA conditions appear likely in southerly flow for the
Bay overnight. Winds will turn out of the west to southwest
tomorrow. Low-end SCA conditions appear possible during the
daytime hours within WSW flow. Additional thunderstorms may form
tomorrow afternoon, and potentially could lead to the issuance
of SMWs late tomorrow afternoon or tomorrow evening. Sub-SCA
level northwesterly winds are expected over the waters on
Friday.

SCA conditions possible Sat night into Monday evening with sct-nmrs
thunderstorms.

&&

.TIDES/COASTAL FLOODING...
Southerly winds will lead to elevated tidal anomalies through
the end of the week. Annapolis is forecast to reach Action
Stage during high tide through tomorrow morning. However,
outside of freshwater influences from heavy rainfall, the threat
for tidal flooding appears low.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flood Watch until midnight EDT tonight for DCZ001.
MD...Flood Watch until midnight EDT tonight for MDZ004>006-008-011-
     013-014-503>508.
     Flood Watch until midnight EDT tonight for MDZ003-501-502-509-
     510.
VA...Flood Watch until midnight EDT tonight for VAZ036>040-051-053-
     054-501-502-505-506-526-527.
     Flood Watch until midnight EDT tonight for VAZ025>031-503-504-
     507-508.
WV...Flood Watch until midnight EDT tonight for WVZ050>053-055-
     501>506.
MARINE...Flood Watch until midnight EDT tonight for ANZ530.
     Small Craft Advisory from midnight tonight to 1 PM EDT
     Thursday for ANZ533-534-537-541-543.

&&

$$

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