Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 140807

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
407 AM EDT Mon May 14 2018

.SYNOPSIS...A front over the area will lift north late today
and tonight then drop southward again Tuesday night and
Wednesday when it will become stationary across the area through
Friday. The front may lift north again during the weekend.



Earlier showers and thunderstorms have exited stage right early this
morning, moving off the Delmarva and in to the western Atlantic as
we speak. Currently, there are no echos being observed by the local
radars and temperatures are generally in the upper 50s to lower 60s.
We are seeing some areas of locally dense fog thanks to the low
clouds and plentiful moisture from the recent precipitation.
Visibilities could drop to below one mile at times early this
morning, so use caution while traveling.

The stationary boundary that has remained stretched across our CWA
the past couple of days will begin lift northward today, likely
residing across northern MD this evening, and eventually lifting
north into Pennsylvania on Tuesday. With the assistance of passing
mid level energy this afternoon and the proximity of the boundary,
we are expecting another round of strong to severe thunderstorms
this afternoon. Shower and thunderstorm activity across the Ohio
Valley later this morning will move in to our western zones by
midday, and reaching the metro areas later this afternoon. A Slight
Risk for severe storms encompasses portions of our area, mainly
south of the I-70 corridor and west southwest of the District,
including much of the Shenandoah Valley and portions of the Potomac
Highlands, which is where the warm sector is forecast to reside.
Ample CAPE of 1000-2000 J/KG and sufficient 0-6km shear values of 30-
40 kts will promote conditions favorable for primarily damaging wind
gusts, with a lesser threat of hail. Convection will wane during the
evening hours with a drier trend expected overnight. Temperatures
will settle in to the mid to upper 60s after seeing highs top out
today in the low to middle 80s.



The stationary boundary will lift further northward on Tuesday,
residing across Pennsylvania by Tuesday afternoon. Much warmer
conditions expected on Tuesday as a result with highs reaching the
lower 90s, and humidity values well above normal. Continued showers
and thunderstorm chances expected Tuesday afternoon, with another
Slight Risk of severe storms possible for much of the area. Shear
values will be less on Tuesday, but strong to severe storms will be
possible with sufficient instability and lift. The stationary front
dips back southward across our area on Wednesday, bringing continued
threat for showers and afternoon thunderstorms once again.
Temperatures will be cooler Wednesday with ample cloud cover and
showers around, with highs topping out around 80, and lows in the
mid to upper 60s both Tuesday and Wednesday nights.



Tropical moisture will be funneled northward across the mid
Atlantic states Thu-Fri between a mid-upper level trough over
the lower MS valley and a strong subtropical ridge over the
western Atlantic. A stationary front across the area will also
act to enhance rainfall over the area. In addition, largely
unidirectional flow Thu night also suggests potential for
training convection. The Thu night-Fri period looks like the
wettest period of the week particularly late Thu night into Fri
morning. Widespread amounts of 1 to 2 inches appear likely
during this period. 13/18Z MMEFS guidance show potential for
river flooding based on the 10 to 50th QPF percentiles. Given
all the ingredients described above and increasingly wetter
soils, some flooding appears likely this week, but location and
timing are still uncertain. It does appear though as the I-95
corridor would be the most vulnerable to flooding.



IFR/LIFR conditions being observed across the terminals early this
morning with low CIGs and VIS restrictions due to fog, while winds
remain light and variable. These restrictions will continue through
early this morning before improving by mid-morning, likely returning
to VFR until early afternoon. Showers and thunderstorms will return
to the terminals this afternoon, bringing episodes of sub-VFR
condtions once again, with winds favoring a more southerly

The persistent stationary boundary will lingering across the Mid
Atlantic through midweek, bringing plenty of clouds and rain chances
to the terminals. Sub-VFR conditions will be possible through this
period as a result, with winds generally remaining 10 knots or less,
outside of convection.

IFR conditions seem likely Thu night-Fri morning with heavy



No headlines expected through tonight with light winds prevailing
over the waters. Afternoon and early evening showers/thunderstorms
will once again cross the waters, bringing the threat for gusty
winds which could result in Special Marine Warnings. SCA conditions
possible during the day on Tuesday as southerly winds increase and
become gusty. Sub SCA conditions likely return through Wednesday
night as light winds prevail. With the persistent stationary
boundary remaining near the area, periods of showers and
thunderstorms will continue each day, bringing the possibility for
Special Marine Warnings should conditions warrant.

SCA conditions possible Fri afternoon into Sat in southerly



Minor coastal flooding possible at Annapolis and Straits Point
during the late evening/early morning high tide cycle next few
days. New minor coastal flood thresholds are expected to be
implemented on Tue for Annapolis and Straits Point assuming
there is no flooding ongoing which may temper the coastal flood
threat somewhat.


MD...Coastal Flood Advisory until 8 AM EDT this morning for MDZ014.
     Coastal Flood Advisory until 4 AM EDT early this morning for


TIDES/COASTAL FLOODING...LFR is the U.S. government's official web portal to all federal, state and local government web resources and services.