Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 141920

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
320 PM EDT Mon Aug 14 2017

Weak high pressure will linger over the Mid-Atlantic region
through tomorrow. A series of disturbances will move up from the
southwest bringing rain chances to our region into tomorrow. A
second area of high pressure will build into the region around
mid-week, before a cold front slides across the region later in
the week.


Clouds and light rain showers will cover the northern half of
our region the remainder of the afternoon. Rain amounts are
averaging a few hundredths of an inch to one tenth of an inch.
Although the NAM represents current rain coverage better than
the GFS, it has been about 3 to 4 hours too slow with current
showers. With temperatures in the middle to upper 70s and dew
point temperatures in the middle to upper 60s, it is making for
a rather sticky afternoon in areas that do not receive any rain


Although we anticipate rain showers to become more widely
scattered in the mountains and along portions of the Mason-
Dixon region this evening and tonight, there will be some rain
showers lingering and other showers developing in parts of the
Shenandoah Valley and Virginia Piedmont as well. Very little
thunder expected in the rain activity into tonight. In the
western Atlantic, Tropical Storm Gert churns up the waters of
the western Atlantic before eventually moving north and
northeast out to sea through midweek.

Weak disturbances and a lingering surface trough will lead to
other shower activity Tuesday into Tuesday night. Thunder is
possible Tuesday afternoon but limited instability will result
in minimal chances. Temperatures will be a couple of degrees
warmer with dew point temperatures poking up into the lower 70s
in many places.

High pressure will build into the region Wednesday into
Wednesday night. Drier and slightly cooler conditions will
develop over the region.


A weak upper level ridge will be moving over the region
Thursday, while at the surface, a warm front will be advancing
back north across the region. The end result will be a
significant warm up, with temperatures possibly reaching 90 for
the first time in quite a while (since August 4th at DCA, August
2nd at BWI, and July 24th at IAD). With the frontal passage,
however, we will have a returning risk of showers and t-storms.
We will be solidly in the warm sector on Friday as well, so if
we don`t make it Thursday, we could definitely still get there
Friday. By then however, a shortwave and cold front will be
approaching, which will result in an increased risk of showers
and t-storms, perhaps with a severe threat. The timing of the
next cold front crossing the region is still a bit uncertain,
with various models depicting a range from Friday night to
Saturday. However, by Sunday, we should be solidly behind the
front with cooler and drier weather taking hold, and likely
remaining through Monday.



VFR conditions expected at all terminals with occasional MVFR
in light rain showers through tonight or in patchy fog later
tonight. Sub-VFR conditions with additional rain showers Tuesday
and Tuesday night. VFR conditions Wednesday with high pressure
building into the region.

Main concern Thursday and Friday will be possible intervals of sub-
VFR cigs and vis due to thunderstorms. Risk is mainly
afternoon/evening hours both days, as is typical with


Winds sub SCA this afternoon through Wednesday night. High
pressure will be overhead during the day Wednesday into
Wednesday night.

Winds mainly sub SCA Thursday and Friday, but will need to watch for
potential southerly channeling as a warm front moves through
and the next cold front approaches. Other concern will be
potential gusty winds with thunderstorms, which will be possible
both Thursday and Friday.




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