Ashburn, Virginia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

491
FXUS61 KLWX 170105
AFDLWX

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

.SYNOPSIS...
High pressure will build into the area through Thursday before
moving offshore Thursday night. A warm front will pass through
Friday and high pressure to the south will dominate the weather
pattern for Saturday. A cold front will pass through late in the
weekend before settling to the south early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
With high pressure moving in, winds will continue to diminish
overnight. Favorable pattern for radiational cooling with light
winds, clear skies, and dry air. This will yield low temps about
10 degrees below average for most locales. Therefore, have
maintained frost/freeze headlines where the growing season has
started aside from the warmer areas east of I-95. A hard freeze
is likely in the Shenandoah Valley with lows in the upper 20s.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
High pressure will remain overhead Thursday while heights rise
behind the departed upper-level trough. More sunshine is
expected with a milder afternoon. The high will slowly move
offshore Thursday night and a warm front will pass through the
area Friday. Timing of the warm front is a little uncertain, but
it does appear that it will pass through most areas to allow
for a breezy and much warmer afternoon. Perhaps the boundary may
get hung up over northeastern MD for a bit. Friday night will
turn out dry and warm with a southerly wind behind the warm
front.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
A very complex flow pattern will evolve across the CONUS during the
long term period, leading to much greater than normal forecast
uncertainty.

Models are in reasonably good agreement that by Saturday morning a
positively tilted trough comprised of multiple shortwave
disturbances will extend from the Desert Southwest northeastward
toward the Upper Midwest. A cold front will reside along the
southeastern periphery of this trough, extending from the Southern
Plains northeastward through the Mid-Mississippi Valley toward the
Great Lakes. Surface high pressure will reside offshore, with upper
ridging in place across the Southeast. Such a pattern will favor
south to southwesterly flow on Saturday and well above normal
temperatures as a result. Current forecasts call for temperatures to
reach well into the 80s at lower elevations, with 70s in the
mountains. Most of the day should turn out dry, but a few
showers and a thunderstorm may approach northern Maryland in the
evening.

Thereafter, forecast uncertainty increases markedly, with both
deterministic models and their respective ensembles showing
considerable spread. This spread is illustrated well by comparing
the GFS vs the Euro and Canadian. The GFS maintains one coherent
trough, which progressively lifts northeastward over time, placing
us on the warm side of the system on Sunday, with a strong cold
frontal passage and much cooler air following for Monday. On the
other hand, the Euro and Canadian break the initially positively
tilted trough to our west into two pieces. The northern half of the
trough rapidly progresses to our east on Sunday, causing high
pressure to build to our north at the surface in its wake, and a
back door cold frontal passage to occur, leading to much cooler
temperatures on Sunday. The southern half of the trough is left
behind as a cutoff upper low over the center of the country, which
is subsequently picked up by a trailing trough. Southerly flow out
ahead of that system would lead to a warming trend early next week,
following cooler conditions on Sunday.

To further illustrate the uncertainty, ensemble members from the
GEFS, EPS, and GEPS showing considerable spread for Sunday
through Tuesday. Along with that, there`s also uncertainty with
respect to precipitation. The current forecast calls for low-
end chances for showers each day, which seems reasonable given
the uncertainty.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
Winds diminish tonight and shift to a southerly direction Thu
and Fri.

VFR conditions and south to southwesterly winds are expected on
Saturday. Forecast uncertainty increases substantially by Sunday,
but most outcomes favor VFR conditions.

&&

.MARINE...
SCAs continues for the Bay and lower Tidal Potomac River
through tonight. Lighter winds are expected Thu into Fri, but
southerly winds will pick up later Friday into Friday night and
an SCA may be needed.

Winds may approach low-end SCA levels in south to southwesterly flow
on Saturday. Uncertainty with respect to wind speed and direction
increases substantially by Sunday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory until 6 AM EDT Thursday for MDZ008.
     Frost Advisory from 2 AM to 9 AM EDT Thursday for MDZ003>006-
     008-011-503>508.
VA...Frost Advisory from 2 AM to 9 AM EDT Thursday for VAZ028-030-
     031-036>040-050-051-053-055-056-501-502-505-506-526-527.
     Freeze Warning from 2 AM to 10 AM EDT Thursday for VAZ025>027-
     029.
WV...Frost Advisory from 2 AM to 9 AM EDT Thursday for WVZ051>053.
MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ530>534-
     537-539>541-543.
     Frost Advisory from 2 AM to 9 AM EDT Thursday for ANZ530.

&&

$$

SYNOPSIS...BJL
NEAR TERM...BJL/CPB
SHORT TERM...BRO
LONG TERM...JMG
AVIATION...BJL/BRO/JMG/CPB
MARINE...BJL/BRO/JMG/CPB