Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 161442
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1042 AM EDT Wed May 16 2018

.SYNOPSIS...
A front will remain nearly stationary across the region through
Saturday. Ample moisture, from a non-tropical low pressure
system over the northeast Gulf of Mexico and Bermuda high
pressure off of the Southeast U.S. Coast, will produce wetter
than normal conditions through Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Regional radar mosaic at 1430Z shows scattered light showers
moving across the CWA. A cluster of moderate showers is moving
across southeast Virgina, and through continuity, should cross
the southern portions of the central Chesapeake later this
morning.

From 14Z surface theta-E surface analysis, stationary front
appears to be paralleling the tidal Potomac. Based on this, I
have removed thunder north of this front for today. Expecting
increased coverage of showers today with daytime heating,
however I am not seeing any forcing mechanism other than just
general isentropic lift. With this, the threat of flooding and
severe weather is decreased today and tonight, with the greatest
chances of flooding south of the front across the Virginia
Piedmont where the greatest instability exists late this
afternoon into early evening.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
The heaviest rainfall during the middle to latter part of the week
looks like it will be Thursday afternoon and Thursday night. This
will likely lead to the region having an extended and increasing
flood threat through Saturday, which is highlighted in detail in the
flood section of this discussion.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Surface and upper level low will reside near the Ohio Valley region
on Saturday with likely POPs area wide thanks to deep southerly flow
and supportive PVA. Conditions look to be drier on Sunday as the
main trough axis migrates to our north and into the New England
states, resulting in a more westerly flow aloft as high pressure
builds in to the region. The drier conditions look to be short lived
as a cold front approaches from the northwest Monday and Tuesday,
bringing an increase in rain chances once again. Expect temperatures
to run near normal in the middle to upper 70s on Saturday with the
increased rain chances and cloud cover. Temperatures will return to
above normal, especially for nighttime lows, for the remainder of
the period with highs in the low to mid 80s and overnight lows well
in to the 60s.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
MVFR/IFR all terminals today and tonight, primarily due to low
CIGS. Unusually moist airmass and a boundary will remain nearby
through the weekend. Low cigs along with showers and possible
thunderstorms are expected.

Sub VFR conditions likely on Saturday with rain showers a plenty and
possible thunderstorms impact the terminals. Drier conditions return
on Sunday with brief high pressure building over the region,
bringing a return to predominate VFR VIS/CIGs. Winds through the
period will remain light and southerly at 10 knots or less.

&&

.MARINE...
Mainly sub SCA conditions forecast this weekend, with the
greatest threat to promoting adverse boating conditions would be
passing showers/thunderstorms over the waters on Saturday and
Saturday night. Drier conditions forecast on Sunday with winds
remaining below headline criteria.

&&

.HYDROLOGY...
The surface boundary currently resides across the northern tier
of our CWA this morning, and shows no signs of deviating from
this position very much for the remainder of the week. With a
deep and near-persistent moisture feed from the Gulf and
Atlantic pumping moisture in through at least Saturday, and that
boundary remaining somewhere nearby, this will act as a recipe
for heavy rain potential...which is starting to look like more a
matter of when and how much, rather than if.

At this time, widespread rains of 2 to 4 inches, with locally higher
amounts, are expected through Friday, and although things get less
certain later on in the forecast period, there`s potential for even
more rain after Friday. These amounts of rain would definitely be
sufficient (given already saturated soil and elevated streams) to
cause flooding/flash flooding almost any day through the forecast
period, with some potential for significant river flooding late in
the week through the weekend.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 11 AM EDT this morning for DCZ001.
MD...None.
VA...Coastal Flood Advisory until 11 AM EDT this morning for VAZ054.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...KLW
NEAR TERM...Lee
SHORT TERM...KLW
LONG TERM...BKF
AVIATION...BKF/KLW
MARINE...BKF/KLW
HYDROLOGY...Lee/JE



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