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

low pressure will remain along the coast through today.
Backdoor cold front will cross the area Friday afternoon and night. High
pressure will build for the Labor Day weekend.


Near term /through tonight/...
upper-level ridging is expected to continue between a departing
shortwave off the North Carolina coast and shortwave energy moving
into the Ohio Valley this afternoon.

No change in airmass is expected today with hot and humid
conditions continuing. Temperatures will reach the upper 80s along and
west of the Blue Ridge to the low to middle 90s near the I-95
corridor. The heat and humidity will lead to more instability
today with MLCAPE values around 1-2j/kg of MLCAPE developing.
There is a lack of a strong lifting mechanism today compared to
Wednesday so convection is not expected to be as as widespread.
However...with a light flow in place this is favorable for terrain
circulation to act as a weaker lifting mechanism.
The lift from terrain circulation should be enough to trigger
isolated to scattered thunderstorms along and west of the Blue
Ridge this afternoon into this evening. Did allow for isolated
convection toward the Washington metropolitan area and southern Maryland
for a period this evening due the light northwest steering flow.

A backdoor boundary will approach the region from the north and
east late tonight...this may trigger a couple more showers but
forcing will be weak and due to the unfavorable timing any shower
coverage should be isolated. Temperatures in the upper 60s to low 70s.
Patchy fog is possible especially in areas that receive rain


Short term /Friday/...
high pressure builds in from the northeast
Friday as a backdoor cold front moves into North Maryland Friday morning.
This will bring an airmass change for the weekend. The front will
sag southward Friday and showers are expected to form Friday
morning and into the afternoon. Thunderstorms are also possible
Friday afternoon. Easterly flow behind the front will lead to
onshore flow and showers and thunderstorms may increase in
coverage. Eastern slopes such as the Blue Ridge foothills may
experience rainfall enhancement due to upslope conditions. At this
time due to recent dry conditions no flood threat is imminent
however this will need to be watched closely.


Long term /Friday night through Wednesday/...
backdoor cold front will be crossing the area Friday night with scattered
showers/T-storms ending from east to west late Friday night. Low
clouds are expected to get bank up against the Blue Ridge and
Appalachians mountains on easterly flow. Low clouds will then gradualy
mix out Sat morning.

High pressure builds for the weekend giving way to fair weather through
Labor Day. However...GFS is suggesting some moisture will be
advected from the Atlantic into the Chesapeake Bay as a weak low pressure
(possible remnant low of erika) lifts northeast. For now will
continue to keep forecast dry as this seems a low probability outcome
according to gefs ensemble data.

Surface high pressure weakens further middle next week while moisture
gradually increases increasing the risk of showers and T-storms.
Temperatures will also be on the rise through middle next week with
90s making a return. Weak frontal passage indicated by GFS and
European model (ecmwf) in the Wednesday-Thursday time frame but ensembles show a high degree
of uncertainty with respect to timing. Also...high pressure building
behind front looks pretty weak so front may not get enough push to
make it through the area.


Aviation /14z Thursday through Monday/...
VFR conditions expected through this evening. An isolated
thunderstorm cannot be ruled out this afternoon and evening...but
most of the time should be dry. Any thunderstorms that do develop
will cause sub- VFR visibilities and possible gusty winds. A cold front
moves from NE to SW Friday. Rain showers/thunderstorms in the vicinity expected mainly in the
afternoon. Some ts may produce heavy rain.

Low clouds expected Friday night along and west of the Blue Ridge Friday
night into Sat morning with IFR ceilings likely at kcho. Some remnant
smoke from the Great Lakes may also be advected into the region from
New England.


high pressure will cause light northwest winds over the waters
today into this evening. A cold front will move into the waters
from the NE Friday morning. Winds will become NE from north to S on
the waters. Winds will also begin to gust near Small Craft Advisory conditions by
Friday afternoon. A Small Craft Advisory is possible Friday afternoon into Friday

Small Craft Advisory conditions appear likely Sat into Sat evening especially on
the Chesapeake Bay. Small Craft Advisory possible again on Monday.


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


near term...bjl/has
short term...has
long term...lfr

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