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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
1021 am EDT Sat Jul 30 2016

Synopsis...
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.

&&

Near term /through tonight/...
showers approaching the catoctins and south of Fredericksburg mark
the leading edge of 850 mb warm nose. There aren't many other
synoptic features of note this morning.

The 12z lwx radiosonde observation depicts a marginally unstable atmosphere to start
the day. Modified for anticipated afternoon conditions yields
around 1400 j/kg MLCAPE amidst 30 kt effective shear. Therefore,
given sufficient heating, conditions are in place for thunderstorm
development.

As the overnight forecaster noted, it will be interesting to see
how the morning clouds/showers interact with the building
instability. Could see two scenarios: either thunderstorms develop
along differential heating boundaries and/or terrain circulations
initiate convection which organized and propagates off the
mountains. Am leaning primarily on the latter, with the support
of cams, but am not completely ruling out some activity in the
I-95 corridor in the early afternoon. The main source of synoptic
lift will be isentropic.

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. Given the current uncertainty in details, have opted
to leave the flash flood threat in the severe weather potential statement. The other hazard would
be from localized downbursts, assuming that updrafts can become
strong enough.

Have indicated a gradual diurnal diminishing trend to the pops,
although some uncertainty exists due to the wavering front as well
as continued warm air advection. The upglide could support storms into the
evening; this would be a larger concern for Washington
District of Columbia/Baltimore City.

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.

&&

Short term /Sunday through Monday night/...
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 precipitable water 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
precipitation.

&&

Long term /Tuesday through Friday/...
troughing aloft and ridging at the surface will provide for
relatively pleasant and dry early August weather for Tuesday and
Wednesday. European model (ecmwf) hints at possible convective system in northwest 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.

&&

Aviation /14z Saturday through Wednesday/...
VFR conditions across the terminals at this time (aside from mrb
where a shower just crossed). Additional storms anticipated to move
east from the mountains this afternoon. Heavy rain and gusty winds
will be possible. Am trying to be more targeted with timing, but
that will be a challenge. The late afternoon-evening hours most
likely to see flight restrictions, which should be localized and
brief but significant (ifr or lower).

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.

&&

Marine...
light S/southeast flow expected through the morning. There could be an
increase, especially on the wider waters, this afternoon and
evening; still have it capped at 15 kt. 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 west/northwest winds on Monday.

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

&&

Tides/coastal flooding...
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.

&&

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

&&

$$
Synopsis...ads
near term...hts/ads
short term...ads
long term...mm
aviation...hts/ads/mm
marine...hts/ads/mm
tides/coastal flooding...mm

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