Area Forecast Discussion
Issued by NWS Sterling, VA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
FXUS61 KLWX 300804

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
404 AM EDT Sat Jul 30 2016

A weak front will remain across the area today and tonight. An
area of low pressure will track along the front on Sunday. The
front will move southward on Monday, with high pressure building
in for the middle portion of the week.


Surface features are somewhat nebulous this morning, as a weak
boundary remains across the Mid-Atlantic to the Ohio Valley, and
a second boundary over northern NC. Obs indicate some patchy light
fog across the region, although mid and high clouds will be

Cluster of showers in the Roanoke-Lynchburg vicinity indicated the
leading edge of a theta-e ridge which will be advecting northward
this morning ahead of a baggy 850 mb low over the Ohio Valley. There
is some model spread as to whether this will result in only
scattered showers, or if more significant convection develops as CIN
erodes by mid-morning.

This evolution could affect the remainder of the day and whether
there is a break as the nose of the moisture convergence pushes into
PA. If this is the case, the secondary generation of storms this
afternoon would be over the higher terrain, slowly drifting east
this evening. If not, there could be a rather muddled conglomeration
of storms over mainly the northern part of the area. Needless to
say, an unsettled day is expected with low confidence in the details.

These details are mildly important due to the moisture rich airmass
which will be in place, a deep warm cloud layer, and steering flow
around 20 kt. This could lead to a localized flash flood threat,
especially in areas which have seen heavy rain in recent days.
However, given the best convergence is expected to lift into PA,
have opted to leave in the HWO for now. Also, if morning/midday
precip is spotty or quickly exits, sufficient destabilization could
lead to a few strong storms with deep layer shear around 30-35 kt.
An isolated damaging wind gust would be the primary threat.

Have indicated a gradual diurnal diminishing trend to the POPs,
although some uncertainty exists due to the wavering front. Highs
today will depend on the amount of cloud cover and precip, but could
approach 90 in a few spots. Lows tonight will be the the upper 60s
to lower 70s for most.


On Sunday, upper level troughing will gradually spread east from the
Ohio Valley, and weak low pressure will track along the stalled
front. Combined with modest destabilization, this will likely be
enough for additional showers and thunderstorms to develop,
particularly during the afternoon and evening hours. Overall
moisture quality looks to be lower Sunday with a more westerly low
level flow, but PWAT will still be seasonably high, so more locally
heavy rain can`t be ruled out. As the low tracks east, should see
activity taper off overnight.

On Monday, the mid-level trough axis will be crossing the area, and
a secondary surface trough may also provide some convergence.
Therefore, at least a few scattered storms will be possible. This
axis will swing east during the evening, allowing a quick end to


Troughing aloft and ridging at the surface will provide for
relatively pleasant and dry early August weather for Tuesday and
Wednesday. ECMWF hints at possible convective system in NW flow
around the periphery of another building central US ridge, but will
disregard for now given difficulty of pinpointing these systems days
in advance, and tendency of them to curl southward into greater
instability. Highs in the 80s and dew points in the 60s under mostly
sunny skies.

Ridging aloft begins to build back into the area by the end of the
week with hotter weather likely returning. Thursday/Friday still
look relatively dry, with perhaps a few isolated showers/storms,
mainly terrain driven, with some moisture return. Highs back up to
around or above 90F.


BWI/MRB are nearing MVFR vsby this morning, but encroaching mid and
high clouds should keep the fog in check. Complex forecast today for
showers and storms. There may be at least scattered activity
spreading from S to N across the area during the morning, with
perhaps a break before additional storms move east from the
mountains this afternoon. Heavy rain and gusty winds will be
possible, especially with the afternoon storms...while the morning
showers may carry a period of lower cigs.

Storms will likely diminish this evening. There is a decent signal
in guidance for fog and/or low clouds tonight; however am hesitant
to bite on it this far in advance.

Additional thunderstorms could develop Sunday afternoon and evening
as a front drops into the area. A few storms can`t be ruled out for
Monday either as the front finally pushes south.

Predominantly VFR expected Tuesday and Wednesday of next week. Only
restrictions may come in some patchy fog at night/early morning.


Light S/SE flow expected through the morning. There could be an
increase, especially on the wider waters, this afternoon and
evening, but have capped at 15 kt for now. Gusty winds from
thunderstorms will be a threat as well. Overall, light flow is
expected through Monday, with the main hazard coming from scattered
afternoon and evening storms each day. A cold front will bring a
shift to W/NW winds on Monday.

Near-SCA conditions are possible Tuesday on northerly flow with high
pressure building in. Winds decrease Wednesday.


Tidal anomalies under a half foot this morning will increase this
afternoon and tonight as southeast low level flow increases and
additional rain/thunderstorms develop. Minor coastal flooding
possible with tonight`s/early Sunday morning`s high tide cycle,
especially Annapolis/Baltimore.




TIDES/COASTAL FLOODING...MM is the U.S. government's official web portal to all federal, state and local government web resources and services.