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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
311 am EDT Wed Aug 31 2016

weak high pressure will remain near the mid-Atlantic coast today. A
cold front will pass through the area late tonight into Thursday
and high pressure is expected to build overhead for Friday through
the weekend.


Near term /through today/...
a few showers still ongoing early this morning across central
Virginia along dew point/moisture gradient. These should continue
to dissipate by sunrise. Some patchy fog also around, which will
also dissipate near or shortly after sunrise. Otherwise, another
hot day with highs reaching 88-92f across much of the area. This
warmth, coupled with dew points in the mid to upper 60s will allow
for modest instability to develop this afternoon, on the order
of about 1000 j/kg or so. Cold front will still be well west of
the area through the day, but expecting a Lee trough to develop,
which along with the higher terrain, will be focii for convective
inititaion this afternoon. Heading into the evening hours, with
mean westerly flow, should see convective activity gradually move
eastward and towards the metros.

With only marginal instability and shear (25-30 knots 0-6km), not
anticipating a significant severe threat, however, can't rule out a
few stronger to marginally severe thunderstorms. Also noted is
surge of precipitable water values over 2 inches, which will
allow for an environment conducive for localized heavy rain.
However, with recent dry weather, and expectation that storms
should be moving at about 10-15 knots, not anticipating too much
of a flood threat.


Short term /tonight through Friday night/...
ongoing convection for the first half of tonight will gradually
wane, however could see a few scattered showers/thunderstorms at
just about any time overnight as cold front pushes southeastward
and to a point near the I-95 corridor by sunrise Thursday
morning. Lows still relatively mild, generally 65-73f.

Cold front will continue crossing the region on Thursday. Upper
level trough and associated energy holds back well behind front
however, so risk continues through the day for scattered showers
and a few thunderstorms. Highs several degrees cooler behind
front and in presence of added cloud cover, only in the upper 70s
to low 80s.

Flow pattern becomes a bit more convoluted towards the end of the
week, but general idea is that upper trough remains overhead Friday,
with surface high building in from the north, keeping the tropical
entity currently in the Gulf (td #9) to the south and east. This
should allow for a pleasant day with mostly sunny skies Friday.
Temperatures will be near or slightly below normal, with highs in
the upper 70s to low 80s.


Long term /Saturday through Tuesday/...
high pressure will remain overhead for Saturday and
Sunday...bringing dry conditions along with low humidity. Will
have to watch what is now tropical depression 9. This system is
expected to pass by to our south Saturday. Please see the National
Hurricane Center for the latest forecasts regarding dew point 9. Should
this system track farther to the north and west...then some
precipitation may approach parts of the area over the weekend.
However...the latest 00z European model (ecmwf) and GFS along with the gefs mean
shows this system remaining further south and east.
Therefore...the forecast will lean toward continuity which keeps
dry conditions in place.

High pressure will remain overhead for Monday as well before
shifting to the east during the middle portion of next week.
Warmer and more humid conditions will return during this time.


Aviation /06z Wednesday through Sunday/...
predominantly VFR expected through today. Some patchy early morning
fog at cho/mrb may bring a period of MVFR before lifting around 12z.
Otherwise, will see development of scattered showers/thunderstorms
this afternoon which may bring brief periods of reductions later
this afternoon and evening.

Tonight, forecast depicts mainly VFR conditions. There is the
possibility of a low stratus deck developing and moving into the
region as cold front pushes into the region. Some light patchy fog
also possible in areas that see rain today.

Any possible stratus/fog will lift giving way to VFR conditions as
drying northerly flow develops behind front. Some scattered
showers/thunderstorms also remain possible. Patchy fog possible
Thursday night/early Friday morning, with mostly sunny skies and VFR
conditions expected Friday.

High pressure will remain overhead for Saturday and Sunday. A
north to northeast flow is expected during this time along with
VFR conditions.


winds generally 5-15 knots out of the south/southeast today. There
may be a period of small craft conditions tonight as southerly
winds increase out ahead of an approaching cold front. Have
currently shown gusts 15-17 knots, and will monitor for
possibility of a Small Craft Advisory. A few showers/thunderstorms
also possible later this evening and into tonight.

Winds turn northerly behind the front Thursday afternoon, and
increase Thursday night and into Friday. Small craft advisories
may be needed Thursday evening through Friday night.

High pressure will remain over the waters for Saturday and Sunday.
Tropical depression 9 is expected to pass to the south of the
waters Saturday. See the National Hurricane Center for the latest
forecasts regrading tropical depression 9. The gradient between
the high to the north and lower pressures from the tropical system
may cause gusty winds Saturday. A Small Craft Advisory will likely
be needed for portions of the waters Saturday into Saturday night.

High pressure will remain over the waters for Monday.


Tides/coastal flooding...
tidal anomalies are near normal early this morning. The anomalies
should increase a bit today into tonight due to a southerly
flow. Water levels will be close to minor flooding thresholds
during the high tide cycle late tonight into Thursday morning.
However...latest forecasts keep them just below at this time
thinking that the winds should be light enough to prevent larger
jumps in the tidal anomalies. Winds will turn to the north later


ranking of Summer 2016 in terms of average temperature (jun 1 - Aug 30)

Site rank average temperature

District of Columbia 3 80.6
balt 14* 77.3
iad 3 77.4

* tied with 1937, 1944, 1994, and 2006

The number of days in August with the high temperature being at or
above 90 for dca is 22 through August 30th. This breaks the
old record of 21 set in 1980.

The number of days in August with the high temperature being at or
above 90 for iad is 19. The record is 20 set in 1980.

The number of days in August with the high temperature being at or
above 90 for BWI is 13. The record is 18 set in 1988.


Lwx watches/warnings/advisories...
District of Columbia...none.


long term...bjl
tides/coastal flooding...bjl

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