Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 260703 CCA

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
141 AM EDT Fri Aug 26 2016

High pressure remains off the coast through tonight. A cold front
will cross the region early Friday. High pressure will return for
the weekend. Another front may slowly slide southward into the
area by the middle of next week.


High pressure will remain offshore tonight and a weak surface
trough will remain overhead. A light southerly flow will allow for
noticeably warmer and more humid conditions overnight compared to
recent nights. Min temps will range from the mid to upper 60s in
the Potomac Highlands and portions of the Shenandoah Valley to the
middle 70s near Washington and Baltimore.

A cluster of showers and thunderstorms have developed ahead of a
cold front over Pennsylvania this evening. This activity will
slowly build south and east toward northern Maryland overnight.
Current feeling is that the activity will weaken as it approaches
our area due to the fact that it will be outrunning the cold
front that will not get here until after sunrise...and there will
be less instability due to the loss of daytime heating. Will have
to monitor this though...because with dewpoints in the 70s there
will be some instability hanging around through the night. Will
continue with slight chance/chance for showers and isolated
thunderstorms across our northern and western zones overnight.

Patchy fog is expected overnight as well due to more low-level
moisture in place and light winds. Fog should be confined to favored
areas in river valleys and rural areas...but fog may be locally


Timing of the surface boundary continues to inch earlier.
Consensus timing looking like daybreak-mid morning from northwest
to southeast. Based on this timing, believe the passage will be
dry. Not only is the timing out of synch with favored diurnal
trends, but west/northwest winds will promote subsidence, and at
all levels above the surface ridging will reinforce that
subsidence. The downslope flow may take the edge off the humidity
but compressional warming may add to the temperature instead. Will
await the 12z ECMWF before deciding tomorrow`s temperature.

Ridging will keep muggy but rain-free conditions in place Friday
night through Saturday night. Temperatures won`t stray far from an
ensemble blend.


Ridge of high pressure aloft sits over our region Sunday while a
frontal boundary slowly approaches Sunday night into Monday. This
boundary will remain near or over our CWA Monday into Tuesday
bringing a chance of showers and thunderstorms. Shortwave energy
moves near our CWA Tuesday night and forecast becomes uncertain
after this. Moisture advection will be affecting our area but
depends on which guidance is used, the source/wind direction
varies. But in general... showers and thunderstorms are possible
Wednesday and Thursday. The forecast will be refined as confidence
increases. Temperatures will be in the mid 80s and low 90s and
heat indexes in the mid 90s.


A weak boundary will slip across the terminals Friday morning,
veering winds west (around 10 kt). These winds will eventually be
northwest by the end of the day. Most moisture will mix out and
any additional clouds will be suppressed.

High pressure will return for the weekend. VFR should prevail.


Status quo on the waters. We`re in a marginal Small Craft Advisory
environment on the waters. Will keep the SCA in place into the

A weak front will slide through on Friday. Flow will veer west
Friday morning, northwest Friday evening, and eventually becoming
east by late Saturday, as high pressure moves to the north. At
this time, sub- SCA conditions expected...but wind gusts may be
close to SCA criteria Friday due to a deep mixing layer. Have
capped gusts around 15 knots for now since there will be a weak
gradient but it will be close.


Water levels about a half-foot above astronomical norms. ESTOFS
depicting its typical water piling in the northern extent of the
Bay. Some of this is a model bias. Believe that caution stages
will be reached. Still have low confidence in Annapolis reaching
minor flood but it will be close (if it does, it will be a
threshold Advisory for a couple of hours). Therefore...have not
issued an advisory at this time.

Winds will become west Friday and north by early Saturday. There
should not be any concerns beyond tonight`s cycle.


Ranking of summer 2016 in terms of average temperature (JUN 1 - AUG 25)

Site         RankAverage Temperature

DC  3 (tie with 2012)80.4
Balt          19 (tie with 2 other years) 77.2
IAD  3 77.2

MARINE...Small Craft Advisory until 2 AM EDT early this morning for
     Small Craft Advisory until 6 AM EDT early this morning for


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