Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 291533
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1133 AM EDT Fri Jul 29 2016

.SYNOPSIS...
An area of low pressure will move offshore this morning, although
a stalled front will remain in place across the area through this
weekend. Another area of low pressure will track along the front
on Sunday. The front will move southward on Monday, with high
pressure building in early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Low pressure currently moving away from the coast, with some low
clouds acorss the southern half of the forecast area. This will
provide the opportunity for daytime heating.

For the rest of today, there will be much less forcing for ascent,
aside from diurnal destabilization. Northerly flow behind the
departing low may also advect some slightly drier air into the
region. However, with the weak boundary still draped across the
area, so can`t rule out a shower or storm from developing.
Modified sounding using forecast high temp in the upper 80s yields
MUCAPE just above 1000 j/kg...substantially lower than past
couple of days. Will focus the higher POPs (but still low chance)
near the mountains, since terrain circulations will likely help
drive the convection. While a few spots could top 90, it`s
finally looking like the majority of the area will remain in the
mid to upper 80s today.

Tonight, some moisture will begin advecting into the area ahead of a
trough to the west. However, forcing will be weak, so will only
carry low POPs for showers. Lows will be in the upper 60s to lower
70s.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Troughing over the Ohio Valley will focus broad ascent on the Mid-
Atlantic for Saturday. Expect shower and thunderstorm chances to
increase throughout the day. Mass fields/moisture transport are less
impressive than Thursday, but seasonably high PWAT will be focused
on the stalled front with weak steering flow, so heavy rain and
flooding could again become a concern. Due to clouds and widespread
precipitation, mid-level lapse rates will be poor, but given
sufficient destabilization, storms could tap into 30+ kt deep layer
shear and become locally strong. Marginal Risk covers this threat
for now.

There should be a break in the precipitation by later Saturday
night. However, as the Ohio Valley troughing moves east, an area of
low pressure will develop along the front on Sunday, once again
leading to an increase in showers and thunderstorms. There isn`t
a strong moisture connection to the Gulf with this round of
storms, so coverage and intensity may be a little less than
Saturday. As the low moves toward the coast and instability
decreases, storms should diminish Sunday night.

Expect temperatures this weekend to be within a few degrees of
normal outside of storms.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Next week will start out with troughing aloft over the Northeast and
Mid Atlantic States, which will provide for some relief from the
heat and humidity that has been prevalent the past couple of weeks.
However, this does appear to be short-lived as ridging builds back
in by the end of the week.

As far as sensible weather, the Monday through Wednesday time period
should feel a bit more pleasant with reduced humidity and highs
generally in the 80s and lows in the 60s. By late week however, will
see temperatures reach back towards 90F. Pattern will be less active
as well, with some lingering showers/thunderstorms possible Monday
as base of trough swings through, but then drying out for much of
the remainder of the week, aside from an isolated shower or
thunderstorm.

&&

.AVIATION /16Z FRIDAY THROUGH TUESDAY/...
Still have patchy MVFR conditions at DCA/IAD and MTN. VFR still
looks increasingly likely by midday, since these lower clouds
will burn off. Large parts of today and tonight should be dry.
Threat of late day thunderstorms non-zero, but much too low to
justify a TAF mention.Will hold off on including fog in tonight`s
forecast for now as cloud cover could be abundant.

Showers and thunderstorms will be likely both Saturday and Sunday,
focused on the afternoon and evenings. Saturday has the better
potential for heavy rain and locally strong storms.

Predominantly VFR expected Monday and Tuesday of next week. A few
lingering showers/thunderstorms possible Monday, and some patchy fog
possible at night.

&&

.MARINE...
Gradient flow has relaxed in the past hour. Winds presently below
Small Craft Advisory thresholds. In light of these developments
and anticipated evolution through the afternoon, have cancelled
the Small Craft. Threat of storms looks low today and tonight.

Gradient winds should be light for the remainder of the weekend. The
best chance for slightly increased flow will be as a low pressure
system crosses the area. Gusty thunderstorms could occur both
Saturday and Sunday during the afternoons and evenings.

Mainly Sub-SCA conditions expected Monday and Tuesday. Some
lingering showers/thunderstorms may produce some locally gusty winds
on Monday.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies around one-half to one foot above normal early
this morning have led to a few sites to crest above minor flood
stage. Anomalies should lessen this afternoon, but further high
tides will need to be monitored over the next couple of days,
especially at our most sensitive site, Annapolis.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...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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