Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 291049
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
649 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/...
Earlier convection has morphed into stratiform, synoptically-driven
rain as an area of weak low pressure moves off the coast. This rain
should be departing the area around daybreak. Some light fog may be
found in its wake.

For the rest of today, there will be much less forcing for ascent,
and lower clouds may hang around well through the morning. 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 and potential for embedded vorticity in the flow
aloft, can`t rule out a shower or storm from developing. Will focus
the higher POPs (but still low chance) near the mountains. 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 /12Z FRIDAY THROUGH TUESDAY/...
An area of rain crossing the area is resulting in IFR conditions at
times. While the rain should largely exit the area by the morning
push, the low clouds may linger along with light fog. Am not certain
how quickly these cigs will lift, but VFR looks increasingly likely
by midday. Large parts of today and tonight should be dry. 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...
Early this morning, winds are generally 10 kt or less on the waters.
Have continued the Small Craft Advisory since low pressure will
still be moving away and there could be a surge of slightly higher
winds this morning...although for the most part, models have
backed off. As a result, moved the expiration time up to 4 PM, and
this may be cancelled sooner. 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...Small Craft Advisory until 4 PM EDT this afternoon for
     ANZ530>534-537>543.

&&

$$
SYNOPSIS...ADS
NEAR TERM...ADS
SHORT TERM...ADS
LONG TERM...MM
AVIATION...ADS/MM
MARINE...ADS/MM
TIDES/COASTAL FLOODING...MM



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