Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 111426 AAA

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
1026 AM EDT Sun Mar 11 2018

Low pressure will pass south of the area tonight, emerging off
the Carolina coast Monday afternoon. The coastal low pressure
will rapidly intensify as it moves northeastward into the
Canadian Maritimes Tuesday night. Another Canadian high pressure
will build across the central and southeastern U.S. for the
second half of the work week.


Dry weather next 12 hrs under weakening high pressure. Clouds,
however, will be on the increase this afternoon. Highs will be
in the 45 to 50F deg range.

Not anticipating sig changes for late tonight and Monday from
what we have been advertising the past couple of days. We`ll
probably add some winter advisories for late tonight into
tomorrow potentially as far north as Fauquier, Warren and points
west for the afternoon. Still less than a 50% chance that precip
gets to DC by 12Z Mon.

Previous afd...

Clouds continue to increase tonight as low pressure approaches
the area from the south, becoming mostly cloudy area wide by
daybreak Monday. Do think much of the area remains dry through
midnight, with our far southwestern counties in VA being the
first to observe precipitation. Could see a rain/snow mix over
portions these areas to start late this evening, but with
temperatures transitioning to near or below freezing after
midnight, expect a change to all snow. Much of the precipitation
will remain south and west of the metro areas through daybreak,
with several inches forecast in our extreme southwestern zones
through this time. We have upgraded the Winter Storm Watch to a
Winter Storm Warning for Augusta, Nelson, Highland, and the
Central Blue Ridge starting this evening and continuing into
Monday afternoon. We are expecting a total of 3 to 6 inches of
snowfall in these areas.

Confidence in accumulating snowfall reaching advisory criteria
further north and east of these areas is still low at this time.
Additionally, further accumulations to north and east will
occur after sunrise Monday, so will allow the following shift to
assess any advisory/warning expansions.


By Monday morning precipitation will continue to spread north
and east over the area, with the axis of heaviest precipitation
along the southern third of our CWA. As the low moves south of
our area, it will emerge off the Carolina coast by Monday
afternoon and begin to rapidly intensify into Monday evening.
Depending on the track of the low and how far northward
precipitation stretches, will obviously have implications on
snow accumulations across the area. Models have come in to
better agreement with a further northward track compared to the
last couple of days. Still have a few more model runs to digest
that will help hammer out the details and paint a clearer
picture of the potential impacts and accumulations.

Went a bit below model consensus for temperatures on Monday,
keeping temperatures generally in the middle to upper 30s. The
March sun angle will play a role in how much snow can
accumulate, and whether or not we see a rain/snow mix which will
be most likely to happen along and to the southeast of the DC
metro. That being said, still expecting areas along and south of
the I-66 corridor to see the best chance of accumulating
snowfall. As the low intensifies off the VA/NC coast,
precipitation will come to an end by Monday evening and pull
east of the area. Upslope snow showers are expected on the back
side of the system with winds picking up out of the northwest.

Conditions will be breezy and cold for the middle of March
Tuesday and Tuesday night as a strong pressure gradient resides
over the region. Snow showers will be possible during this
period as well, mainly west of the Blue Ridge, as a mid to
upper level trough will reside over the northeastern U.S.


Overall, pattern will be on a warming trend as upper level
trough gradually lifts out and is replaced by a ridge. However,
we will start out chilly and downright wintry with cool temps
and a few snow showers possible even east of the mountains on
Wednesday as a deep shortwave crosses the region, with gusty
northwest winds as well. Upslope snow will continue along the
Allegheny Front. Another shortwave passes on Thursday, but with
diminishing northwest flow and increasing heights, odds of
precip will dwindle and temps will warm. Heights continue to
rise on Friday as the trough continues pulling northeast away
from us, but the ridge will be slow to truely build in. That
said, highs will finally return to near normal. A warm front
then tries to push into the region ahead of an approaching wave
of low pressure on Saturday, resulting in a chance of rain.
Temperatures look near to slightly above normal at this point,
but this will need reevaluation given we may be stuck on the
cool side of a warm front with damming on the east side of the
mountains...guidance could be significantly too warm.


VFR conditions expected across the terminals through tonight,
with CHO seeing sub-VFR conditions approach by daybreak Monday
as rain/snow approaches. MVFR/IFR conditions will be possible
Monday and early Monday night as low pressure passes to the
south and intensifies off the Carolina coast. This will bring
the potential for rain/snow across the terminals, with
reductions in VIS/CIGs. Precipitation will move east of the
terminals by Monday evening, seeing a return to VFR conditions
as a result. Gusty northwest winds will be observed behind the
exiting system through midweek, with gusts upwards of 25 knots
possible. VFR will predominate Tuesday through Thursday.


Sub SCA conditions expect today and through the first half of
tonight with high pressure over our waters. SCA conditions
appear likely for portions of our waters after midnight and all
of our waters through the day on Monday as low pressure passes
to the south before intensifying off the Carolina coast Monday
afternoon/evening. SCA conditions will likely persist into mid
week as a strong pressure gradient will reside over the waters.


VA...Winter Storm Warning from 8 PM this evening to 2 PM EDT Monday
     for VAZ025-036-503-504-508.
MARINE...Small Craft Advisory from 6 AM to 6 PM EDT Monday for
     Small Craft Advisory from 2 AM to 6 PM EDT Monday for ANZ534-


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