Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 251915
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
315 PM EDT Sun Sep 25 2016

.SYNOPSIS...
A frontal boundary will remain stalled to our south tonight while
high pressure passes to our north. The high will move off the
coast Monday. A cold front will pass through the area overnight
Monday into Tuesday. An upper-level low will likely impact the
area during the middle portion of next week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of early this afternoon...a stationary front was sitting to our
south in the Carolinas with high pressure over southeastern
Canada. Easterly flow has promoted cloud development across
southern parts of the CWA...particularly west-central Virginia
where the flow is bumping up the Blue Ridge. Further north, the
high`s influence has been more apparent with drier air and sunnier
skies.

Tonight, a cold front currently in the Mississippi Valley will
push eastward and the high will shift east as well. THis will
cause the flow to gradually become more southeasterly and increase
moisture flow into the region. Low clouds will become more
widespread after diminishing for a time this afternoon and a
little drizzle or perhaps a shower may occur in west-central
Virginia. Further north and east it should stay less cloudy and
radiational cooling should allow temps to drop down into the 50s
and even some 40s.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Cold front will cross the region from west to east during the
period followed by potential cyclogenesis at the end of the period
as a strong upper low drops southeastward towards the area. Monday
morning will start fairly cloudy especially towards the southwest
(west-central VA) where upslope flow will be ongoing. Some drizzle
or showers will be possible here. As we head through the day, the
front will approach and clouds at higher levels will become more
widespread as well. Think highs manage the low 70s before the
clouds get too dense to block the sun completely but its not
impossible most places get stuck in the 60s. Showers will start to
push east from the west as we head through the afternoon but
thunder odds are not high given we stay fairly stable on the north
side of the front over the Carolinas.

Main fgen band with front moves through Monday night. It may slow
down as it crosses the area in response to the upper low dropping
down from the Great Lakes but think it should generally clear the
CWA by later Tuesday. Instability will be minimal since warm
sector will have trouble coming back north ahead of the cold front
(which really will likely pass our area as more of an occluded
front) but forcing aloft with high PW`s may be enough to squeeze
out some thunder. Rainfall amounts very uncertain but a decent
rain on the order of a half inch is expected...perhaps more if the
forcing is strong enough and the front slows down enough. Lows
will stay relatively mild with the clouds and rain Monday
night...50s and 60s...while temps should try to rebound into the
70s on Tuesday after clouds break.

Things get very uncertain as we head into Wednesday. Tuesday night
should start out dry but as the upper low approaches from the west
cyclogenesis may begin in our area by midday Wednesday which would
result in the redevelopment of showers. Still lots of uncertainty
here so have kept highs in the 70s...but if the more pessimistic
scenarios happen we may be stuck in the 60s Wednesday.+


&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
A cutoff upper level low over the Great Lakes will push south and
east towards our area Wednesday night and into Thursday... and
possibly Friday. There is uncertainty on the exact details of the
forecast as guidance is in disagreement with location timing of
the upper level low. If it pushes further south, a coastal low
pressure could develop over the Mid-Atlantic region. With this
scenario the chance of showers over our CWA extends from Wednesday
night and into Friday, and dry conditions into the weekend. If the
upper level low lingers to our west and north then the chance of
showers could extend from Wednesday night into the weekend.
Basically, expect a chance of showers Wednesday night into Friday
and uncertain into the weekend... depending on position of the
upper level low.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Low clouds have been persistent around CHO today and may linger
through tonight into Monday. Further north VFR continues and
should stay that way through tonight into Monday before the front
approaches. However, the low clouds near CHO may encroach
northward late tonight so MVFR cigs are not
impossible...especially at IAD and MRB. Sub-VFR and quite possibly
IFR cigs/vis expected Monday night as front moves through with
rain. Improving conditions by Tuesday afternoon then perhaps
worsening again later Wednesday as another storm approaches.

Sub-VFR conditions possible Wednesday night and maybe into
Saturday as upper level disturbance could bring showers into the
region. Details with this forecast are uncertain as guidance is in
disagreement at this moment.

&&

.MARINE...
Light winds tonight with high pressure, then SCA takes effect
midday tomorrow through tomorrow night with front approaching and
then crossing area with rain. May need to extend into Tuesday
depending on winds behind front. SCA may again develop Wednesday
as another system approaches.

Small craft advisory possible Wednesday night and into Friday as
coastal low could develop off of the Mid-Atlantic coast. Winds
could be diminishing into Saturday but it is uncertain at the
moment.

&&

.TIDES/COASTAL FLOODING...
Despite NEly flow, a surge in water has been noted across the MD
portion of the Chesapeake Bay and the Tidal Potomac. Water levels
have remained below minor coastal flood thresholds on this lesser
high tide (except it was met at Straits Pt this morning).

Washington DC SW Waterfront has their high tide at 4:30pm this
afternoon and the water level will be very close to the minor
threshold of 4.2ft.

The high tide this evening/overnight is the greater of the two
today and weakening NEly flow this evening should aide positive
anomalies to persist. Coastal flooding is expected tonight at
least at Annapolis and the DC SW Waterfront and possible at
Straits Pt, Solomons Island, and Baltimore.

Onshore flow will increase and turn to the southeast for Monday
through Monday night. Minor flooding is likely during this
time...especially during the high tide cycle Monday night which
will be the higher of the two astronomical norms. Should the SEly
winds be a little stronger, a coastal flood watch may be necessary
for Monday night.

&&

.CLIMATE...
Unusually warm weather has persisted over the area for
quite some time. Autumn-like temperatures are finally making an
appearance over the area, and DCA has finally fallen below 60
degrees this morning for the first time since June 9th (total of
107 days). The record most consecutive days at or above 60
degrees in the Washington DC area is 112 set in 2012.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from noon Monday to 6 AM EDT Tuesday for
     ANZ530>543.

&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...IMR
AVIATION...IMR/RCM
MARINE...IMR/RCM
TIDES/COASTAL FLOODING...BAJ
CLIMATE...LWX


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