Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 240038
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
838 PM EDT Wed Aug 23 2017

.SYNOPSIS...
A cold front will settle into southeast Virginia tonight. An upper
level trough will sweep southeastward Thursday and push the
front offshore Thursday night. High pressure will build north of
the area through the weekend and remain in control early next
week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A surface cold front remains off to our south across
southeastern Virginia. However...an inverted trough does extend
north from southern Virginia into central Virginia. A weak
upper-level disturbance is also passing through central Virginia
and southern Maryland this evening. A couple showers cannot be
ruled out across these areas through late this evening.
Elsewhere...it will remain dry and noticeably cooler/less humid.

High pressure will continue to build toward the area from the
Great Lakes and Ohio Valley. This will continue to push the
front south overnight. A northerly flow will allow for cooler
and less humid conditions compared to recent nights. Could see a
sct/bkn deck of clouds underneath the subsidence inversion
around 5kft. Therefore...will carry a partly to mostly cloudy
sky especially near and east of the Blue Ridge Mountains.

Min temps will range from the lower to middle 50s in the Potomac
Highlands to the middle 60s near downtown Washington and
Baltimore into the Virginia Piedmont and southern Maryland.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
High pressure will remain well to the northwest on Thursday with
cyclonic flow aloft. A well defined trough will pass through the
area during the late afternoon and evening. At a minimum, this
will lead to increased cloud cover. Better lift and moisture
(although fairly meager in depth) will be across northern
portions of the area. Have introduced a slight chance of showers
during this time. Highs will be in the mid 70s to lower 80s,
with overnight lows in the 50s to lower 60s. Some patchy fog is
possible in western valleys.

Afterward, sprawling high pressure will remain in control
through Friday night, although its eastward progress will be
limited to the Great Lakes region. Thus the local area will
remain in cold to neutral advection. There will be an early
fall feel to the air, with temperatures about 5 degrees below
normal and dew points in the 50s. Some models try to generate
some QPF in the mountains Friday afternoon and evening with a
slight upslope wind component, but am thinking the atmosphere
will be too dry to support precipitation and have thus left the
forecast dry.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
An upper-level trough will remain overhead for Saturday and Sunday
while surface high pressure remains centered over New England. A
north to northeast flow around the high will usher in unusually cool
conditions for this time of year...making it feel more like late
September instead of late August. A couple showers cannot be ruled
out due to upper-level disturbances associated with the longwave
upper trough overhead...but most of the time will be dry and any
precipitation amounts will be light.

The upper-level trough will slide off to the east Monday and another
upper-level disturbance may approach Tuesday. High pressure will
remain centered over New England...bringing more cool
conditions.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
An isolated shower near KCHO is possible through late this
evening.

High pressure remains to the northwest tonight through Friday
night. This will result in VFR conditions and light northerly
winds. There`s a slight chance of a shower Thursday afternoon
and evening with an upper disturbance. Nocturnal fog is
questionable since the center of the high won`t be overhead.

High pressure will remain centered over New England Saturday
through Monday. A north to northeast flow is expected most of
the time along with VFR conditions. An isolated shower cannot be
ruled out Saturday or Sunday...especially across KMRB and KCHO.
Even for these areas...much of the time will likely be dry.

&&

.MARINE...
The boundary will continue to move south of the waters tonight
and a pressure surge is expected as high pressure approaches
from the northwest. Winds will increase a bit, especially over
the open waters of the Chesapeake Bay and middle/lower Tidal
Potomac River where the gradient will be tighter. Have issued a
Small Craft Advisory for this area from 2 AM until noon
Thursday, although it will be marginal with wind gusts around
18 to 20 knots.

The high should be close enough by that winds will remain below
SCA levels from Thursday night through Friday night, out of a
north to northeast direction.

High pressure will remain centered over New England for
Saturday through Monday...and a north to northeast flow is expected.
Winds may come close to SCA criteria Saturday night and Sunday...but
the better chance for SCA conditions will be Sunday night and Monday
when the gradient strengthens a bit.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 2 AM to noon EDT Thursday for
     ANZ531>534-536-537-539>541-543.

&&

$$
SYNOPSIS...ADS
NEAR TERM...BJL/ADS
SHORT TERM...ADS
LONG TERM...BJL
AVIATION...BJL/ADS
MARINE...BJL/ADS


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