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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
940 am EDT Monday Aug 3 2015

a cold front will approach the area today before stalling out
overhead tonight through Friday. Low pressure will ride a stalled
front...passing through the middle Atlantic Thursday and
Friday before pushing offshore by Saturday. High pressure builds
south then for the weekend.


Near term /through tonight/...
forecast is on track this morning. A decaying squall line is
moving into the Ohio River valley this morning. This will continue
to weaken as it moves south this morning. A surface trough is expected
to form by this afternoon and isolated showers and thunderstorms
can not be ruled out across southern Maryland and surrounding waters as
instability increases in this location.

Previous discussion...
current analysis shows a cold front over the eastern Great Lakes
this morning. Potent upper-level low pressure continues to spin
over the Hudson Bay and the upper-level trough axis associated
with this system extends south into the mid-Atlantic.

The cold front will slowly drop south and east approaching our
area today. Southwest winds ahead of the front along with a deep
mixing layer and plenty of sunshine will allow for unseasonably
hot conditions. Maximum temperatures will reach the lower to middle 90s
across most locations. Deep tropical moisture will remain
suppressed to our south dewpoints should mix down into
the 50s and 60s today...keeping heat indices closer to air

The cold front will move into the region this evening. A Theta-E
ridge ahead of the boundary may increase instability some...and
this will bring the chance for showers and thunderstorms. The best
chance for convection will be across northern Maryland into the
Potomac Highlands where forcing on the boundary will be stronger.
The boundary will stall overhead late tonight...and a couple
showers or thunderstorms may impact the area during this
time...but most of the time should be dry since forcing on the
front will be weak. There will be little temperature gradient
along the front...but it will be warmer and more humid near and
east of the I-95 corridor. Min temperatures will range from the 60s
across most areas west of the Blue Ridge mountains to the middle and
upper 70s near downtown Washington/Baltimore and also east of
Interstate 95.


Short term /Tuesday through Wednesday night/...
the boundary will remain stalled overhead...most likely near
intestate 95 south and west across central Virginia into the
Potomac Highlands. Again...little temperature gradient is expected
along the boundary so most areas will turn out quite warm with maximum
temperatures in the upper 80s to lower 90s for many locations. A couple
showers and thunderstorms may pop up...mainly during the afternoon
and evening hours along and ahead of the boundary.

The boundary will remain nearly stationary Tuesday night...but any
convection should dissipate due to the loss of daytime heating.

The boundary may shift a bit farther south for Wednesday and
Wednesday night...but with a zonal flow aloft it should not move
too far. A westerly flow will allow for more warm conditions
across all areas...but humidity may be a bit higher across
southern Maryland and central Virginia closer to the boundary.
Therefore...a couple showers and thunderstorms are possible across
these areas Wednesday afternoon and evening. However...most areas
should remain dry since the boundary will be weak.

A potent area of low pressure will strengthen over the Midwest
overnight Wednesday. Latest guidance shows this system being a bit
slower than previously forecasted. Therefore...probability of precipitation have been
tweaked down a bit with the latest forecast update. Will continue
with a slight chance/chance for showers overnight but if the
latest trends continue it actually end up dry during this time.


Long term /Thursday through Sunday/...
00z model suite has a weakening stationary front positioned over
southern Virginia by 12z Thursday. Some inconsistencies on surface low pressure
organizing over the Midwest...with all but the GFS developing a
closed low that then proceeds to deepen as it rides the frontal
boundary. Will go with more of the consistent solution and bring
the closed surface low into the middle Atlantic Thursday night. Concerning
precipitation...using this solution would have showers and embedded thunderstorms
overspreading the region during the day Thursday and through the night
into Friday...corresponding with the passage with middle level shortwave
energy. The exact path of the low will dictate the extend of any
thunderstorm activity...with the better chance in the latest runs indicating
central Virginia and south.

The low pushes offshore Friday night with high pressure over Canada
then attempting to build south. Am keeping slight chance probability of precipitation in during
the weekend to account for multiple shortwaves moving through the region
which combined with diurnal heating could trigger showers and possible
even thunderstorms.

Temperatures near or slightly below normal through the extended.


Aviation /13z Monday through Friday/...
VFR conditions are expected most of the time today through
Wednesday night. Southwest winds will gust around 15 to 20 knots
this afternoon. Patchy br may reduce visibilities briefly to MVFR levels
late tonight into Tuesday morning. A shower or thunderstorm is
possible this evening...especially across kmrb but convection
should remain isolated/scattered. A couple showers and
thunderstorms may pop up near the eastern terminals Tuesday
afternoon and evening as well.

Sub-VFR conditions likely Thursday into Friday with developing showers
and thunderstorms. Precipitation will be more occasional in nature during the day
Thursday...becoming more widespread Thursday night and Friday before tapering
off by Friday night. VFR conditions return for the weekend.


a cold front will approach the waters today. A south to southwest
flow ahead of the boundary will strengthen due to an increasing
pressure gradient. A Small Craft Advisory is in effect for the
waters this afternoon and evening. South to southwest winds may
channel up the Bay and lower tidal Potomac River overnight into
Tuesday. A Small Craft Advisory remains in effect for the Maryland
Chesapeake Bay and lower tidal Potomac River tonight...and for the
middle portion of the Bay and lower tidal Potomac River Tuesday

A boundary will remain near the waters for Tuesday and Wednesday.
A couple showers and thunderstorms are possible Tuesday afternoon
and evening. Convection may be suppressed further south Wednesday
afternoon and evening.

Sub-Small Craft Advisory conditions currently expected Thursday and Friday.
Depending on the strength of the low...could see Small Craft Advisory conditions
Thursday night into Friday. Sub-Small Craft Advisory conditions then for the weekend.


Tides/coastal flooding...
tidal anomalies remain below a half foot early this morning.
Southerly flow ahead of an approaching cold front will elevate
tidal anomalies this afternoon through tonight. Water levels may
come close to minor flooding thresholds for sensitive areas
around high tide tonight...and again Tuesday morning.
However...latest guidance continues to keep water levels below
those minor thresholds...which makes sense since this winds are
expected to shift west of south later tonight into Tuesday. Water
levels will have to be monitored...since it will be close.


Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory until 6 am EDT Tuesday for anz530-531-538-
Small Craft Advisory until noon EDT Tuesday for anz532>534-537-
Small Craft Advisory from 3 PM this afternoon to midnight EDT
tonight for anz535-536.


near term...bjl/has
short term...bjl
long term...bjl/Sears
tides/coastal flooding...

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