Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 101415

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1015 AM EDT Thu Aug 10 2017

High pressure will move offshore today. A warm front will lift
north towards the region on Friday while a cold front will
approach the region from the northwest Saturday, then stall in
the region Sunday. A wave of low pressure could move from
southwest to northeast along the stalled front early next week.


Ridge of surface high pressure is located overhead this morning
but will shift offshore throughout the course of the day,
leading to the development of a light southeasterly flow. At the
same time, weak shortwave energy is pushing eastward through
West Virginia this morning with an area of associated showers.
Mostly sunny skies are in place across much of the region this
morning but this will give way to increasing mid/high clouds
from the west as the shortwave moves eastward, as well as a
developing cumulus field this afternoon. Much of the shower
activity will weaken as it moves into the area, however have
increased PoPs across portions of eastern WV and into the
Shenandoah Valley/central Blue Ridge as at least scattered
showers should make it into these locations this afternoon.

Tonight, warm advection will become more pronounced in advance
of the approaching warm front, with clouds becoming more
widespread still, and the chance of showers increasing. Still,
balance of region should stay fairly dry, with showers most
likely to the west of the metros. With the clouds increasing,
lows should stay notably milder, with 60s common.


Low pressure developing along the front just off the coast will
slow its progress northward on Friday, resulting in a fairly
cloudy day as warm advection continues aloft. The chance of
showers with isolated thunder will continue to increase,
especially late in the day and at night as a shortwave crosses
the region. Since surface based instability will be fairly
limited, have kept thunder in chance range. The outliers showing
a more concentrated area of heavy rain with a more consolidated
low pressure center are notable, but for now, we consider them
less likely.

Warm front finally lifts north into the region Saturday,
allowing somewhat warmer air to move in, though right now think
most places will not get above the 80s. However, next cold
front approaching from the northwest will then move in from the
northwest late in the day or at night, then stall over the
region. Upper level support later on Saturday is fairly meager,
so think pops are lower than Friday aft/night, though perhaps a
bit more thundery with a bit more surface CAPE possible. Precip
will mostly dissipate Saturday night with the end of most
forcing, resulting in mainly dry conditions by early Sunday.


Sunday...Zonal flow across the eastern CONUS along with surface
high pressure slowly drifting east across the western Great
Lakes. South winds prevail with Bermuda High Pressure in
control. This is the last day with expected temperatures near
the normal value. Gulf Stream moisture spreads into the area
Sunday with chances for afternoon popup showers/thunderstorms
per the GFS. ECMWF is more bullish with an actual surface low
passing us on Monday.

Canadian high pressure begins to influence the Mid-Atlantic
weather after the low passes (GFS has it well south of the area)
with drying conditions and slightly below normal temperatures
through the rest of the work week.


Dry conditions and VFR expected through today, with an
increasing chance of showers tonight and tomorrow as warm front
approaches the area. There may also be a period of MVFR
ceilings tonight into early Friday, with the greatest risk at
CHO. By late tomorrow and tomorrow night, reduced cigs and vis
in showers and perhaps embedded thunder are a concern.
Conditions improve Saturday as the warm front briefly lifts
north before the next cold front comes down from the northwest
late in the day and at night, but the threat of t-storms will

Afternoon thunderstorms in the DC metro Sunday with a Bermuda
high pressure drifting east. Great Lakes high begins to
influence the area Monday with dry conditions/VFR by Wednesday.


High pressure pushing east of the region through Friday with
warm front lifting north will likely keep winds below SCA,
though showers and perhaps embedded thunder are possible later
Friday and Friday night. Saturday, its possible SCA winds could
develop as the warm front lifts north but before the next cold
front arrives. Thunderstorms will remain possible Saturday,
mainly in the PM.

Generally sub-SCA south winds Sunday from Bermuda high
pressure. Weak cold front crosses into Tuesday with VFR then
under high pressure through the rest of the work week.




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