Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 211420
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1020 AM EDT SAT MAY 21 2016

.SYNOPSIS...
Low pressure will track up the Mid-Atlantic coast today. Upper
level low pressure will persist along the Mid-Atlantic coast
tonight through Monday night. High pressure returns Tuesday and
persists through mid-week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Shield of stratiform moderate to locally heavy rain has been
progressive, and is currently over the Bay...primarily affecting
the Delmarva/southeastern tidewater region. Elsewhere, clouds,
areas of light rain, and perhaps drizzle will be affecting area
through the midday hours.

Low pressure developing atop Cape Hatteras will be moving up the
coast this afternoon. Easterly flow ahead of this low will be
drawing more moisture into the area. That will produce enough
upglide to initiate a new round of showers for northeast Maryland.
Therefore PoPs will be higher there than other areas along the
I-95 corridor.

Secondly, height falls will be advancing into the mountains as
shortwave energy carves out a trough axis. Instability in the
mountains meager, but there will be a couple hundred joules of
CAPE, especially south of W99. Have likely PoPs returning to the
mountains this afternoon, along with a slight chance of thunder.

Am not making any temperature changes at this time. Given the
saturated low levels and easterly flow, it will be a struggle to
see 60 degrees, although central Virginia may manage it.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
The best way to describe the short term period is "unsettled"...
although gradually less so with time through Monday night. As
energy rotates into the upper trough tonight, a closed low will
eventually develop, reaching the Outer Banks by Monday, then
perhaps drifting offshore by Monday night. With the subtlety in
disturbances within this pattern, timing and placing the highest
rain chances will be difficult. Have favored north/west tonight
where greatest height falls and moisture will be. On Sunday, have
brought a period of likely POPs across the area as trough
axis/upper low moves overhead. Can`t rule out some thunder,
although looks like a very minimal chance...best in the far west.
Have calculated a "storm total" through Sunday, which ranges from
less than one inch NE of Baltimore, with 1.5 to 2 inches from DC
south/west. Of course, locally higher is possible.

Expect shower chances to diminish Sunday night, only to renew
Monday, with highest chances in the east closer to the upper low.
There`s a little better chance of a thunderstorm or two on Monday as
it looks like there will be a better chance of seeing some breaks of
sun. The drying trend should begin in earnest Monday night.

Sunday`s temperatures will largely depend on where it rains the
longest, and models differ strongly regarding this. Splitting the
difference maintains continuity of lower to mid 60s. Right now
Monday is looking warmer...in fact guidance is has widespread 70s.
Given unsettled pattern, played conservatively closer to 70.
Overnight lows remain fairly constant in the 50s.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Upper level low pressure will be departing eastward on
Tuesday...with convergence and warming temperatures aloft. Temps
will rise and clouds will break, but still a slight risk of a
shower is showing up in guidance. A ridge axis will approach from
the west Wednesday, continuing the confluence and the warming.
This ridge axis will weaken Thursday as southwesterly flow
develops aloft, but heights will continue to build resulting in
more warming. Instability may result in convective showers or
thunderstorms developing over the mountains and possibly moving
east into the metro. Another weak ridge axis will cross the area
Friday with heights remaining high, though a trough will be
approaching from the west. More showers and storms may form over
the mountains and advect into the metro.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
Shield of rain advancing northeast across the area, and for the
most part have cleared the terminals. Restrictions are taking
some time as atmosphere needs to saturate. MVFR more common at
this point, although CHO/MRB have achieved IFR. Further
restrictions still possible today since low levels saturated.

The forecast for tonight through Sunday night is rather uncertain
with upper level low pressure moving through the region. It will be
unsettled to say the least with MVFR looking likely for much of the
time with occasional showers. Don`t have confidence to time in any
IFR. Monday should see improved conditions but a lingering chance of
showers, especially afternoon.

VFR Tuesday and Wednesday with high pressure regaining control.

&&

.MARINE...
Expect SE to E winds to increase this morning as low pressure
develops off the coast. The strongest winds may actually occur
through midday until clouds and rain can sufficiently limit mixing.
However, no changes to the SCA at this time. Wind should diminish
tonight, but will have to monitor for northerly channeling. N to NW
flow will continue through Monday around 5-10 kt. Light and variable
by Monday night.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>534-
     537>543.
     Small Craft Advisory until 7 PM EDT this evening for ANZ535-
     536.

&&

$$
SYNOPSIS...RCM
NEAR TERM...HTS
SHORT TERM...ADS
LONG TERM...RCM
AVIATION...HTS/ADS/RCM
MARINE...ADS/RCM



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