Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 071514 AAA
AFDLWX

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
1014 AM EST Thu Dec 7 2017

.SYNOPSIS...
Ridging will remain in place through early Friday. Low pressure
will pass east of the area late Friday into early Saturday. A
clipper-like system will cross the region Saturday evening. High
pressure will return Sunday into Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...

Dense cirrus will continue to impact the southern CWA while
low-mid level clouds are expected to move into the Appalachians
later today due to a mid-level disturbance. A few snow showers
are possible over the mtns late today into this evening.
Otherwise, dry with increasing clouds from west to east.

Previous discussion...

A weak perturbation in the 700-500 mb flow will cross the
region this afternoon and evening. A thin deck of low-to-mid-
level cloudiness (broken by mid to late afternoon) is likely
with this wave. It will likely kick off a few snow showers
along the western ridges of the Allegheny Front early this
evening with a coating possible in a few spots. Hi-res guidance
would suggest an inch or less. Latest BUFKIT soundings indicated
some low-level instability and inversion heights of around 6000
feet which suggests flurries may cross the mountains and make
it into portions of northern Maryland and the eastern West
Virginia panhandle (i.e. Cumberland/Martinsburg/Romney/Hagerstown).

More dense high cirrus is expected to build from south to north
across the area tonight in response to another upper jet streak
well ahead of developing low pressure over northern Florida.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Aforementioned surface low pressure (weak and elongated) will
pass well to the southeast of the area over the western Atlantic
late Friday into early Saturday. Most (if not all) of the low to
mid level forcing will remain out at sea. However, PVA ahead of
the 500 mb trough and the right entrance region of a very strong
upper jet should expand the light northwestern edge of the
precipitation shield into at least southern Maryland late Friday
into Friday night. At the onset, boundary layer temperatures
will be marginal, so anticipate a light rain/snow mix. After
sunset, temperatures cool and precipitation becomes all (light)
snow. There is still a small subset of guidance that expands
precipitation much further north and west or gives subtle hints
of banding precipitation associated with the upper jet over
southern Maryland early Saturday morning, but given the current
low track, find it hard pressed that anything measurable would
make it west of I-95. Therefore, have confined PoPs to these
areas, most likely for Saint Mary`s County. Given the light
nature of the precipitation and the marginal boundary layer
temperatures for a good portion of the event, snowfall
accumulations should be an inch or less and confined to far
southern Maryland.

As the surface low ejects into the open Atlantic, a strong upper
low/associated clipper-like surface feature will pivot from
west to east late Saturday afternoon through Saturday evening.
Believe scattered snow showers will result in typically favored
upslope areas as well as northern and central Maryland.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
By Sunday morning, the coastal system will be well into the
Atlantic, and the axis of the initial shortwave will be passing
through. A second shortwave will cross the area Tuesday
afternoon-night. Much like Saturday night, the primary
consequence will be scattered snow showers... primarily across
favored upslope areas, but would not preclude flakes just about
anywhere in the area.

The other result of this weather pattern will be a steady stream
of cold air, which will be reinforced by the passing shortwave.
The first day/night after these shortwaves (Sunday-Sunday night
and Tuesday night-Wednesday) will be the coldest, with highs in
the 30s and lows in the 20s. However the other periods won`t be
that much better.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
VFR expected through Saturday night. Any restrictions in
CIGS/VSBYS should be confined to S MD. Elsewhere, very brief
restrictions are possible in snow showers, most likely Sat eve
over highlands and near/N of Potomac River. Surface ridging
likely results in light westerly flow AOB 10 kts through Sat,
becoming NW 10-20 kts and gusty Sat night in the wake of a cold
frontal passage.

VFR should prevail Sunday-Monday.

&&

.MARINE...

Winds gusting well over 25 knots over the nrn waters this
morning. Have issued an SCA through 21Z. Winds diminish over
the relatively cooler waters late this afternoon and remain
light through Saturday before increasing out of the northwest
Saturday night. SCA will likely be needed by Saturday night,
with gale gusts possible as well by Sunday morning.

A strong Small Craft seems likely on Sunday, although wouldn`t
rule out close to Gale early. Winds will gradually subside
through Monday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 4 PM EST this afternoon for
     ANZ530>533-538>541.

&&

$$
SYNOPSIS...DHOF
NEAR TERM...LFR
SHORT TERM...DHOF
LONG TERM...HTS
AVIATION...HTS/DHOF
MARINE...HTS/DHOF



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