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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
1029 PM EDT Thursday Sep 3 2015

Synopsis...
a weak surface trough will remain overhead through tonight. A
backdoor cold front will pass through late Friday into Friday
night. High pressure will build overhead during the Labor Day
weekend.

&&

Near term /through Friday/...
weakening thunderstorms west of the Blue Ridge as of 0030z. SBCAPE values
dcrsng with loss of daytime heating...though MUCAPE still well
above 2k j/kg. Weak surface trough has nudged east of the area...so no
real surface mechanism to trigger any further development...at least
over western areas. Weak vorticity maximum over eastern PA could dip over
eastern Maryland overnight...with possible showers forming. Any precipitation that
does form will taper off late...with dry conditions by daybreak.
Increased low level moisture especially over the valleys of Shenandoah and
light winds could lead to patchy fog.

High pressure will build over New England on Friday and this will
send a backdoor cold front into our area. An easterly wind will
develop and it will not be quite as hot as today...but still
several degrees above normal. Humidity will remain around with the
main dewpoint and temperature gradient remaining off to our north
and east during the day. The heat and humidity along with the
boundary will cause scattered thunderstorms to develop...mainly
during the afternoon and evening hours.

&&

Short term /Friday night through Sunday/...
the backdoor boundary will stall out near the Allegheny and
Potomac Highlands into southern Virginia Friday night. Convection
should dissipate behind the boundary due to the loss of daytime
heating...but a few showers may continue near the boundary across
the Allegheny and Potomac Highlands toward central Virginia. The
easterly flow will cause plenty of cloud cover to develop due to
moisture off the Atlantic Ocean. Drier air may eventually sneak
into northeastern Maryland toward morning as surface high builds
farther south and west.

High pressure remains anchored over New England Saturday and Sunday.
Onshore flow and clouds will greatly limit temperatures with most
areas Saturday below normal. Maximum temperatures Saturday look to be upper
70s/low 80s. This is particularly for areas west from the Blue Ridge
were upslope flow should produce light rain into the afternoon
hours. Weak cyclonic flow brings some chances for light rain to southern
Maryland Sunday...otw dry. Greater sunshine Sunday should bring maximum temperatures
up to the low to middle 80s.

&&

Long term /Sunday night through Thursday/...
high press dominates conditions for Sun night and Monday bringing
drier conditions for the end of the Labor Day weekend. Both the GFS
and European model (ecmwf) are suggesting a weak low press system will drift north
off the southeast coast that will advect moisture from the Atlantic
into our region Monday into Tuesday. This could bring showers and thunderstorms
to our region... mainly to the southeast of our County Warning Area on Monday and
over all of our County Warning Area Tuesday as the system approaches. High press
builds in on Wednesday before a cold front approaches on Thursday increasing
the chance of showers and thunderstorms. Timing and strength of the cold
front is still somewhat uncertain. High temperatures will be in the low
80s to the upper 90s near the metropolitan area and low 80s to our western
counties.

&&

Aviation /03z Friday through Tuesday/...
outside of fog development tonight...generally VFR conditions
through the taf period. Possible fog at kcho/kmrb...reducing visible 2-4
miles. Any fog that forms will dissipate 13-15z.

Dry conditions Friday morning...with scattered thunderstorms by the afternoon...especially
kcho/kmrb. Timing and location of afternoon convection too low in
confidence to include in tafs at this time. Any thunderstorm could bring sub-VFR
conditions with heavy rains and gusty winds.

Light/vrb winds tonight will become Ely by Friday afternoon. The Ely flow
will aide in lowering ceilings for Friday night.

Onshore flow from high pressure anchored over New England Saturday
and Sunday. MVFR ceilings lift Saturday with VFR then through Sunday.

VFR conditions expected Sun night and Monday.

&&

Marine...
sub-Small Craft Advisory conditions tonight through Friday morning. An easterly flow is
expected to develop behind a backdoor cold front Friday afternoon. Winds
will increase with a pressure surge Friday evening into Friday
night. A Small Craft Advisory remains in effect for the waters
during this time. Scattered thunderstorms may also produce brief
gusty winds Friday afternoon and evening.

Onshore flow from high pressure anchored over New England Saturday
and Sunday. Small Craft Advisory for most waters expected Saturday into the
evening...then some chances again Sunday with most wind currently
expected to be at or below 15 knots.

Sub-Small Craft Advisory conditions expected for Sun night into Monday. Some showers
and thunderstorms possible over the waters.

&&

Tides/coastal flooding...
a north to northwest flow has weakened over the waters and this
has allowed for anomalies to increase. The flow will turn to the
east Friday but it should be light enough to keep water levels
below flooding thresholds.

The easterly flow will strengthen Friday night into Saturday.
Minor tidal flooding is possible near time of high tide.

&&

Climate...
well above normal temperatures are forecast to persist across the
area through Friday. As a result...some sites may approach record
daily high minimum temperatures during the next 24 hours.

Below is a table of record daily high minimum temperatures for
September 4th.

Site.....Record maximum min for Sep 4................
dca...76 (set in 2012 and 1953)..................
BWI...75 (set in 2012/1953/1944/1937 and 1932)...
iad...71 (set in 2012)...........................

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory from 6 PM Friday to 6 am EDT Saturday for
anz530>534-537>543.
Small Craft Advisory from 6 PM Friday to midnight EDT Friday
night for anz535-536.

&&

$$
Synopsis...bjl
near term...bjl/Sears
short term...baj/bjl
long term...imr
aviation...baj/bjl/Sears/imr
marine...baj/bjl/Sears/imr
tides/coastal flooding...baj/bjl
climate...dfh

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