Flash Flood Warning 14, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
904 PM EDT Mon May 21 2018

.SYNOPSIS...
A front will remain over the Carolinas into the Appalachian
Mountains today through tonight. The front will return north as
a warm front on Tuesday with a cold front expected to pass
through the area on Wednesday. Weak high pressure will build
over the area for the second half of the week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Showers and thunderstorms in advance of a (very) slow moving
warm front have been rather persistent over the highlands of
eastern West Virginia and west-central Virginia the last few
hours. Low-level warm/moist advection and residual instability
should allow these storms to continue until around midnight
before gradually weakening. Isolated instances of flooding are
possible given high PWAT air and slow storm motion.

Precipitation should gradually weaken and become less widespread
as it pushes east overnight. Still, scattered showers and a
thunderstorm or two are possible into Tuesday morning ahead of
the slowly advancing warm front. Patchy fog is expected as well
but widespread dense fog seems unlikely with scattered to broken
cloud cover moving overhead tonight.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
After some morning low clouds and patchy fog, the warm front
will lift northward, although the extent of which is still in
question. This should place much of the region in the warm
sector by mid-afternoon Tuesday, especially DC southward.
Therefore, instability in this region will increase with MLCAPE
values progged to reach 1000-1500 J/KG. While shear will be
modest, on the order of 25-30 knots, this combination will
likely be enough to support a few strong to isolated severe
thunderstorms, and the region has been placed in a Marginal
Risk for severe thunderstorms. Synoptically, an area of low
pressure will be moving into the eastern Great Lakes, with a
cold front trailing into the Ohio Valley. Across the Mid-
Atlantic states, a lee trough is expected to develop, and will
likely serve as the focus for thunderstorm development Tuesday
afternoon, with convection then moving eastward. An area from
the Blue Ridge east and DC south currently appears to have the
highest chances of seeing stronger thunderstorms.

In addition, with precipitable water values in excess of 1.5"
and saturated soils, the risk of some isolated incidents of
flooding will be increased.

High temperatures Tuesday will range from the mid 70s to low
80s.

The cold front will then approach the area Tuesday night, and
while convection associated with the frontal boundary should be
weakening, some may make it into western/central MD and eastern
WV late Tuesday evening. Lows Tuesday night in the 60s.

The front should complete its crossing the first half of
Wednesday and settle across North Carolina Wednesday night. A
few lingering showers and isolated thunderstorms may be around
Wednesday, although coverage should be much less than Tuesday.
Dry conditions area-wide are then expected Wednesday night.
Highs Wednesday will range from 80-85F with lows in the 50s/60s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
A high pressure system will shift eastward into our region from the
Great Lakes region on Wednesday. Winds look to remain mostly
light and variable. 850 and 700 mb humidity levels look to
remain fairly low which will lead to mostly clear skies Thursday
through Friday. The high will shift eastward off the eastern
seaboard. A south to southwesterly flow will form leading to
weak warm air advection developing. Temperatures will trend
upward moving into the weekend. High temperatures on Thursday
will be in the upper 70s to mid 80s and will slowly trend up
into mid to upper 80s on Friday.

On Saturday, a strong south to southwesterly flow will be in place
over the region due to a high pressure sitting off the eastern sea
board. Temperatures will rise up into the upper 80s to lower 90s.
Rising temperatures and influx of tropical moisture from the gulf
will lead to a chance for some shower and thunderstorm development.
Sunday, the interaction of tropical moisture and higher temperatures
along with a approaching cold front from the west will lead to
increased chances for precipitation and thunderstorms.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
A warm front gradually approaching from southern Virginia will
lead to the development of lower stratus with MVFR/IFR ceilings
likely by early Tuesday morning. There is also the potential
for some patchy fog/br.

The front will then move northward Tuesday morning before a
weak cold front passes through Wednesday. Conditions will
gradually improve during the day before scattered showers and
thunderstorms develop Tuesday afternoon and evening. These
showers/storms will then wane Tuesday night, although chances
will linger into Wednesday.

Light winds and mostly clear skies on Thursday will lead to VFR
conditions. Friday, a weak southerly flow forms but VFR
conditions are expected.

&&

.MARINE...
A few gusts to around 20 knots have been observed early this
evening but will diminish with the loss of mixing. A front will
then approach the waters tonight from southern Virginia and
cross the region Tuesday, before a cold front passes through
Wednesday. Showers and thunderstorms are likely Tuesday,
especially during the afternoon and evening hours. Some storms
may contain gusty winds. South to southwest winds will increase
on Tuesday, followed by northwest flow behind the cold front
Wednesday. Winds may reach SCA criteria Wednesday.

A high pressure system will influence the region leading to
light and variable winds Thursday. No small craft advisory is
expected. A southerly flow is expected to form Friday leading to
winds flowing northward up the Chesapeake.

&&

.TIDES/COASTAL FLOODING...
Freshwater continues to decrease as water levels on the Potomac
River upstream have crested and they continue to fall.
Therefore, the threat for moderate flooding has ended. Minor
flooding is still expected near times of high tide through
tonight, and it is possible Tuesday for Washington DC. Will
continue with the advisory through tonight, and it may need to
be extended into Tuesday as well.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 6 AM EDT Tuesday for DCZ001.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

SYNOPSIS...MM
NEAR TERM...MM/DHOF
SHORT TERM...MM
LONG TERM...JMG
AVIATION...MM/DHOF/JMG
MARINE...MM/DHOF/JMG
TIDES/COASTAL FLOODING...LWX

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
754 PM EDT MON MAY 21 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0641 PM     FLOOD            3 SSE PETERSBURG        38.96N  79.11W
05/21/2018                   GRANT              WV   911 CALL CENTER

            THREE AREAS OF WATER FLOWING OVER DERGON ROAD BETWEEN
            NORTH MILL CREEK ROAD AND THE HARDY COUNTY LINE.

&&

EVENT NUMBER LWX1800362

DH

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
925 PM EDT MON MAY 21 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0845 PM     FLOOD            1 E YANKEETOWN          38.68N  78.93W
05/21/2018                   ROCKINGHAM         VA   911 CALL CENTER

            HIGH WATER OVER YANKEETOWN ROAD.

&&

EVENT NUMBER LWX1800366

DH