McLean, Virginia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

739
FXUS61 KLWX 281835
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
235 PM EDT Sat Jun 28 2025

.SYNOPSIS...
A warm frontal boundary will continue to lift north of the area this
afternoon leading to warmer temperatures, humid conditions, and
scattered thunderstorm chances across the region. Additional showers
and thunderstorms are likely Sunday as a weakening cold front drops
southward into the area. Shower and thunderstorm chances continue
Monday and Tuesday as a stronger cold front pushes through. Less
humidity and drier conditions are expected late next week.


&&

.NEAR TERM /THROUGH TONIGHT/...
The CAD wedge has eroded this afternoon with the warm front
lifting into southeast PA. Some patchy low and mid-level clouds
are leftover across central and northeast MD, but for the most
part the cloud deck has lifted. Mostly sunny to partly cloudy
skies are expected for the remainder of the afternoon with a
bubbling CU field in the vicinity of the lee side trough east of
the Alleghenies and along the departing warm front in south-
central PA. Thunderstorm development has already taken place in
this area (central/southern Shenandoah Valley) with hi-res CAMS
showing a slow jog of convection eastward heading into the
early evening. With the sunshine back in place and light south
to southwesterly winds, temperatures have been allowed to climb
back into upper 80s and low 90s. Mountain locations will be a
touch cooler in the low 80s. Heat index values will hover close
to 100 degrees east of US-15 with mid 90s further west. This
will put us just shy of Heat Advisory criteria with fairly moist
airmass (i.e dewpoints in the low to mid 70s) and limited dry
air in the mid levels mixing down.

Synoptically, high pressure will continue to push further out into
the Atlantic allowing the warm front to work northward heading
into mid-afternoon. Meanwhile, a surface trough will reside in
the vicinity of the I-81 corridor as 850-925mb westerly
downsloping flow ensues in the lee of Appalachians/Alleghenies.
This trough will become the main focal point for convection this
afternoon and evening (between 19-00Z/3-8pm). Convection
appears to be loosely organized (i.e pulse or multicellular
clusters/segments) feeding off of MUCAPE values of 2500-3500
j/kg and 0-6 km shear values of less than 25 kts. 0-1 SRH values
are expected to hover between 15-30 m2/s2 with DCAPE hovering
between 600-900 j/kg. This should allow for some movement with
the storms today although locally damaging winds and isolated
instances of flash flooding appear to be the primary concerns.
PWATS will continue to remain high hovering between 1.7-2.3
inches yielding efficient rain rates of 1-2"+/hr.

Showers and thunderstorms should initialize around I-81 between
now-5pm before slowly drifting east toward the metros between
4-8pm tonight. An isolated shower or storm could pop further
east along the river/bay breeze, but confidence in the evolution
of this remains low at this time. Storms gradually diminish
through the late evening hours (01-03z/9-11pm) with loss of
daytime heating, with mainly dry conditions through the
overnight hours. Some patchy fog can`t be ruled out late
tonight, especially in locations that receive thunderstorms
during the daylight hours. Overnight low temperatures will be in
the upper 60s to the west of the Blue Ridge, and lower to
middle 70s further east.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Additional shower and thunderstorm chances are possible for portions
of the area Sunday as a decaying weak cold front drops southward
into the region. Current 12z CAM/synoptic guidance place this
boundary in the vicinity of the I-66/US-50 corridor or just south of
it into central VA Sunday afternoon. The boundary will have little
impact on temperatures with highs once again reaching back into the
upper 80s and low 90s. Humidity may drop off a little bit especially
for those the further north of I-66/US-50 where modeled PWAT values
look to fall into the 1.1 to 1.4 inch range Sunday afternoon and
evening. Areas south of I-66/US-50 will continue to deal with the
rich moisture laden air with PWATS around 2 inches. This will be the
primary area for convective development (south of I-66/US-50) Sunday
afternoon. SPC continues to maintain a Marginal Risk for most of
central and eastern VA during this timeframe with locally damaging
winds from wet microbursts and instances of flash flooding as the
primary threats. Storms will diminish with the loss of daytime
heating Sunday night with lows once again falling back into the
upper 60s and low 70s.

More widespread shower and thunderstorm activity is possible Monday
especially in northern parts of the forecast area as a washed out
front sits nearby. At the same time, will monitor the progression of
pre-frontal trough off to the west and encroaching strong cold front
approaching from the Ohio River Valley Tuesday. A warm and humid
airmass remains in between these two systems yielding ample
instability and subtle shear for storms to feed off of especially
during the peak heating period. SPC once again highlights the entire
area for a Marginal Risk (Level 1 out of 5) for severe weather.
Locally damaging winds and isolated instances of flooding will remain
possible with CAPE values greater than 2000 j/kg, 0-6 km shear
values less than 30 kts, and PWATS around or /above 2". Highs Monday
will climb back into the upper 80s and low 90s with heat index
values hovering close to 100 degrees. Lows Monday night will sit in
the low to mid 70s.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Potent shortwave-trough and accompanying sfc cold front will cross
the area Tuesday afternoon and bring an organized threat of severe
thunderstorms Tuesday afternoon into the evening. The main threat
will be damaging winds given expected fast storm motions, ample
shear. and strong instability.

After trough axis passes Tuesday night, height rises and building
high pressure will result in seasonable warm and dry/tranquil
conditions through the remainder of the week. A reinforcing dry cool
front will push through the area Fri bringing cooler and drier air
mass for the upcoming Fourth of July weekend.


&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
Pockets of MVFR conditions remain mainly north and east of KBWI
and KNAK. This is in association with a warm front that
continues to lift north and east of the region. VFR conditions
are expected otherwise at all terminals with SCT-BKN ceilings
hovering between 030-070 feet. Sub-VFR reductions are likely at
times this afternoon and evening due in part to thunderstorm
development along a lee side trough east of the Allegheny
Mountains. Highest confidence of thunderstorms appears to be
west of a line from KIAD-KCHO-KLYH with lesser confidence
further east. Thunderstorms appear to be widely scattered with
convective initiation around KMRB-KSHD between 18-21z/2-5pm
before a slow advancement east toward KIAD-KCHO between 20-
23z/4-7pm. Areas further east into the corridor will likely see
any residual convection fire thereafter 21-00z/5-8pm. Convection
should be more isolated further east with the loss of daytime
heating. Left PROB30s in to encompass this threat given the
lower confidence going forward in time. Storms will pack a punch
with locally damaging winds and heavy rainfall along with
frequent lightning. Convection will slowly diminish between
01-03z/9-11pm this evening with perhaps a leftover shower along
and east of the corridor. Areas of patchy fog are possible
tonight with vsbys remaining MVFR or greater at most of the
terminals outside of KCHO. Winds today will remain out of the
south/southwest at less than 10kts.

Additional showers and thunderstorms are possible Sunday afternoon
and evening as a decaying cold front sags southward into the region.
VFR conditions will prevail for most with sub-VFR reductions at
times for terminals south of KIAD and KDCA. Highest coverage of
thunderstorm activity looks to be down around KCHO-KSHD-KLYH-KRIC
with limited to no coverage up toward KBWI-KMRB where slightly
drier/stable air will push in. Winds will switch to the northwest at
less than 10 kts.  VFR conditions at all terminals Monday with
exception to brief MVFR conditions in strong thunderstorms during
the afternoon and evening hours. Numerous showers and thunderstorms
expected Tuesday afternoon, some possibly severe with damaging
winds. Dry conditions expected Wednesday and Thursday.

&&

.MARINE...
Sub-SCA level winds are expected to continue through Monday morning.
Winds will generally be out of the south and south west today before
becoming light and variable Sunday. SOutherly winds return Monday
with some channeling possible especially over the open and
middle waters Monday afternoon and evening. Expect the chance of
an SMW or two each afternoon and evening through Monday as a
result of scattered showers and thunderstorms. SCA conditions
expected late Monday night into Tuesday as the gradient
tightens ahead of an approaching cold front from the Ohio River
Valley.

SCA conditions likely Tuesday-Tuesday night. Severe t-storms are
likely Tuesday afternoon, which may require SMWs.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$

SYNOPSIS...EST
NEAR TERM...EST
SHORT TERM...EST
LONG TERM...LFR
AVIATION...LFR/EST
MARINE...LFR/KJP/EST