Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 230742
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
342 AM EDT Wed Aug 23 2017

.SYNOPSIS...
A cold front will drop southeastward across the mid-Atlantic region
today, before stalling over southeast Virginia tonight. Upper level
energy will sweep southeastward tomorrow and push the front offshore
tomorrow night. High pressure will quickly follow tomorrow night and
persist right on into the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Current radar shows a few patches of light rain showers in parts of
central Maryland and in parts of the northern Shenandoah Valley. A
cold front extends across southern Pennsylvania in the vicinity of
the Mason-Dixon line but angled from north of Harrisburg,
Pennsylvania to near Cumberland, Maryland. This front will continue
to move toward the south-southeast, generate additional scattered
showers, and slide across our entire region today into this evening.
Any rain showers that do develop ahead of or along the front should
produce a few hundredths of an inch to one tenth of an inch this
morning through midday. Showers or perhaps any thunderstorms could
develop during the afternoon but would be mainly across or near
southern Maryland and between Fredericksburg and Richmond in eastern
Virginia. Heavier downpours could occur with this activity as
precipitable water values are at or near the 2 inch mark. It is
during the late afternoon and evening hours that the cold front is
expected to stall, bisecting the Delmarva Peninsula and extending
southwestward into southeast Virginia. As we proceed into the
overnight hours, clouds and precipitation chances decrease and slide
to the east. Temperatures will be nearly 10 degrees cooler than
yesterday across much of our region with humidity values on the
downward trend as well. High temperatures will be mainly in the
middle 80s with low temperatures tonight dropping down into the
lower 60s.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Thursday will consist of two factors of weather. One of them an
upper level disturbance dropping out of the Lower Great Lakes region
into the mid-Atlantic region. This disturbance will help to kick the
stalled front over southeast Virginia out to sea and could produce a
couple of sprinkles in the northern Potomac Highlands. The other
factor will be a firm ridge of high pressure that will build in from
the northwest about the same time as the disturbance moves
southeastward. The high pressure will strengthen behind the passing
disturbance to give us a couple of periods of dry conditions and
comfortable temperatures from Thursday right through Friday night.
High temperatures Thursday and Friday will be near 80 with low
temperatures Thursday night and Friday in the upper 50s to near
60.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
The weekend forecast will still be dictated by high pressure over
northern New England. As has been advertised for a couple of days,
temperatures/humidity levels will be almost fall-like. The only
precipitation potential will come over the mountains at the end of
the day...and that would be limited to a stray shower.

Little will change for early next week, other than the center of the
high will move offshore. That could lead to a bit more moisture
flowing onshore, which may enhance diurnal/terrain showers.
We`re still talking about a small chance, with isolated to perhaps
at worst scattered coverage. And since water temperatures are in the
upper 70s, forecast air temperatures wouldn`t change much.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions expected at all terminals through Friday night. Any
stray showers near the CHO terminal would be mainly this morning and
reduce conditions to MVFR briefly. Winds will be variable around 5
knots most of today ahead of the cold front but are expected to
shift to the northwest at 5 to 10 knots with higher gusts once the
front has passed across the terminals. Winds will be generally
northwest to north 5 to 10 knots tonight through Friday night with
typical diurnal fluctuations each afternoon.

VFR conditions anticipated this weekend under high pressure.

&&

.MARINE...
No marine hazards expected today and tonight. Small craft advisories
may be needed Thursday with diurnal heating during the day and cool
advection aloft. No marine hazards expected Thursday night
through Friday night.

Winds this weekend should be light (at or below 10 kt) under the
influence of high pressure.

&&

.TIDES/COASTAL FLOODING...
Water levels are presently running between a half and three-quarters
of a foot above astronomical predictions. As a cold front crosses
the area, winds will gradually veer west, and then northwest, which
should assist in blowing the tides out of the area. Even in advance
of the front, departures in the Virginia waters are lower than the
Maryland waters, which suggests that departures won`t rise further,
and will have an opportunity to drop this morning.

The latest guidance suggests that Annapolis will be on the cusp of
minor flooding. If the current anomaly holds, then Annapolis will
peak right at the 2.4 ft minor criteria. Do not have the confidence
that this will/won`t happen. Since its a difference of an inch, will
hold off for now. May need to issue a short fused Advisory if I`m
wrong.

All other sites forecast to crest under thresholds, although some
Action Stages will be threatened.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 5 AM EDT early this morning for
     ANZ530>534-536>543.

&&

$$
SYNOPSIS...KLW
NEAR TERM...KLW
SHORT TERM...KLW
LONG TERM...HTS
AVIATION...KLW/HTS
MARINE...KLW/HTS
TIDES/COASTAL FLOODING...HTS


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