Area Forecast Discussion
Issued by NWS Sterling, VA

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483
FXUS61 KLWX 231846
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
246 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 /THROUGH TONIGHT/...
Surface cold front is located across southeast Virginia this
afternoon, with north/northwest flow established over most of
the CWA. Dew points are falling through the 60s and into the
50s, except in the southeast. Light showers are occurring along
the mid level front across southeastern portions of the area.
Some additional development is possible across central Virginia
to southern Maryland as thicker clouds clear and a shortwave
trough approaches. However, instability is weak and drying will
continue to take place through the column, so thunder is
questionable.

The front will only be slowly moving to the southeast tonight,
so cloud cover may be slow to erode south and east of
Washington. Otherwise a pleasant night is in store with low
temperatures ranging from the mid 50s west to mid 60s east.

&&

.SHORT TERM /THURSDAY 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 /18Z WEDNESDAY THROUGH MONDAY/...
Cold front is south of the terminals this afternoon, but close
enough by (along with upper disturbance) to have a lingering
chance of a shower at CHO. Felt coverage and chance of thunder
were low enough that I have not included it in the TAF.

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, mainly at MRB. 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...
Cold front is south of the waters with north to northwest flow
established. Thunder chances this afternoon and early evening
continue to look slim, but will not rule out an isolated storm
or two. A bit of a pressure surge will arrive tonight as the
front moves farther south. Winds will increase a bit, especially
over the open waters near southern Maryland where the gradient
will be tighter. Have issued a Small Craft Advisory for this
area from 2 AM until noon Thursday, although specifics may need
to be adjusted as details become clearer.

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 ANZ533-
     534-537-543.

&&

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



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