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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
355 am EDT Wednesday Sep 2 2015

Synopsis...an upper-level disturbance with its associated surface
trough will pass through the region today. Weak high pressure
will build overhead Thursday before a backdoor cold front moves
into the area late Friday into the weekend.



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Near term /through tonight/...an expansive area of high pressure persists
across the eastern Continental U.S. This morning. A shortwave trough is
located across in/Ohio this morning. A moisture plume is rounding
the top of a 500mb ridge located across the southeast Continental U.S..

Thin middle-high level clouds are moving across the middle-Atlantic this
morning. Warm and humid conditions persist with dewpoints in the
upper 60s to low 70s. Even with cloud cover patchy fog has developed
in low lying locations. Fog is expected to increase in coverage this
morning and into the morning commute. Some breaks in the cloud cover
are possible this morning and will aide in fog development. Fog
should disspate shortly after sunrise. An isolated shower may pop
up this morning west of the Blue Ridge as a shortwave trough
nears.

The shortwave trough will move toward WV/Virginia today. This coupled
with temperatures in the low to middle 90s and elevated dewpoints will result
in showers and thunderstorms breaking out today. The region of
concern is west of the Blue Ridge especially the SW where the best
forcing from the disturbance will be located. Severe threat is low
due to the weak field field due to the upper level ridge.
However...500-1000 j/kg of ml cape is expected even with some
cloud cover and therefore some thunderstorms are expected. Further
east...a surface trough will form around the I-95 corridor/ches Bay.
This may cause a few showers to pop up this afternoon near the
waters. Some showers and thunderstorms may move east of the Blue
Ridge due to weak southeast flow aloft. Coverage is expected to decrease
as they move east today and areas east of the Potomac River may
stay dry all day. Temperatures in the upper 80s near and west of the Blue
Ridge and the low to middle 90s near I-95 today.

The shortwave trough will dive into NC tonight and activity will
move to the south by midnight. Dry conditions will move into the
region overnight however due to no airmass change...warm and
humid conditions will persist with overnight temperatures in the 60s/low
70s and middle 70s in the metros.

&&

Short term /Thursday/...the surface trough will move east Thursday
and be located along the East Coast. Nearly flow is expected across
the region. 850mb temperatures are expected to increase from Tuesday/Wednesday and
therefore Thursday has the potential to be the hottest day of the
week. Several disturbances will be upstream and cloud cover may
cut down on the temperatures Thursday. A few showers are possible
Thursday afternoon mainly west of the Blue Ridge. An isolated
thunderstorm is also possible.

&&

Long term /Thursday night through Tuesday/...a backdoor cold
front will enter northeast Maryland late Friday and move southward across the
rest of the area Friday night. Scattered showers and/or T-storms can be
expected along and ahead of the front Friday evening with activity
lingering longer along the I-64 corridor and Charlottesville area.

High pressure surface and aloft builds quickly late Friday night through
sun leading to very dry conditions and cooler temperatures. While
it is expected to be sunny much of the weekend...aerosol optical
depth (aod) output from the international cooperative for aerosol
prediction multi-model ensemble (icap mme) shows remnant smoke
from the Great Lakes region getting shunted southeastward into the
middle-Atlantic Friday into the weekend as steering winds become more
northeasterly. So...potential for air quality issues over the
weekend under stagnant high pressure system.

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Aviation /08z Wednesday through Sunday/...sub-VFR visibilities possible mainly
at mrb-cho-iad this morning. Clouds should limit dense fog
development but the humid airmass has already led to 3-5sm in
nearby locations. VFR conditions expected today. Rain showers/thunderstorms in the vicinity is
possible mainly at mrb-cho this afternoon. Some activity may move
into iad-dca but confidence is low. Activity will move to the
south tonight and sub-VFR visibilities due to fog are possible again into
Thursday morning. VFR conditions expected Thursday.

Backdoor cfdnt will cross the area Friday night with shifting winds.
Risk of showers and T-storms will be ending from northeast to
southwest Friday night. Also...potential for visbility restrictions
Friday into the weekend as aerosol models suggest smoke getting
shunted southeastward from the Great Lakes region into the mid-Atlc.
Building high pressure surface and aloft and strengthening subsidence
inversion could further complicate things.

&&

Marine...a surface trough is expected to form later today and a few
showers may pop up this afternoon. Winds should stay light below
10kts through Thursday. Surface trough moves east of the waters
Thursday.

Frontal passage expected Friday night with shifting winds. Winds
could approach Small Craft Advisory criteria Friday afternoon and Saturday. Remnant
smoke expected to get transported into the region over the weekend
could result in visibility restrictions.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...none.

&&

$$
Synopsis...lfr
near term...has
short term...has
long term...lfr
aviation...has/lfr
marine...has/lfr

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