Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

FXUS61 KLWX 150052

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

A front over the area tonight will lift north on Tuesday, then
drop southward again Wednesday. It will continue to meander
across the region through Friday. The front may lift north
again during the weekend.


The strong to severe storms will clear the Bay and lower Tidal
Potomac River by 10 pm this evening.

Anvil showers will persist for a few hours behind the storms
late this evening for areas near and east of the Blue Ridge and
Catoctin Mountains before clearing out overnight.

The backdoor boundary that mixed out may re-develop near the
Potomac River, and an upper-level disturbance passing by to our
north may trigger a couple showers overnight, but the boundary
is weak so coverage should be isolated to widely scattered.

Breaks in the clouds and plenty of low-level moisture around
from recent rainfall suggests that areas of fog and low clouds
are possible overnight. Locally dense fog is possible. Lows
will still be mild, with 60s for most areas.


After stalling across the area tonight, the front should lift
handily north of the region on Tuesday, with southwest flow
becoming dominant. This is in response to a weak wave of low
pressure pushing east to our north, which should then cause the
front to drop back south across the region Tuesday night and
Wednesday. We should warm up substantially on Tuesday in the
warm sector, with temps into the low 90s, which will aid in
destabilization as the front drops back south Tuesday night, so
another severe weather risk is present, though the shear is

We should end up cooler overall on Wednesday as the front
settles to our south, but another wave of low pressure will ride
eastward along the front late in the day and at night, so while
we will be more stable, another round of showers and t-storms
looks likely as we head through Wednesday into Wednesday night.
The severe risk should be reduced, however. Highs will be
cooler, and our current forecast may in fact be notably too
warm, with some guidance suggesting highs will get stick in the


A low pressure system looks to be positioned in the northern
Gulf of Mexico early on Thursday. An approaching upper level
short wave trough ejecting out of the lower MS valley, along
with a strong subtropical ridge over the western Atlantic will
funnel moisture from this system into our direction Thursday
into Friday. With the stationary front still parked over the
region, this will only enhance rainfall even more. Thursday
night into Friday looks to be the timeframe where the heaviest
rain will fall. Ensemble guidance suggests that 1 to 2 inches of
rain could fall in many areas. This additional rainfall,
combined with what will already have fallen in the past several
days leads to concerns over flooding, especially along the I-95
corridor. Temperatures during this period will remain around
average, as clouds and precipitation will keep things from
getting too warm.

The aforementioned shortwave lifts into our area some time
Saturday into Sunday. This should help to push the
aforementioned stationary front out of the region. However,
model guidance is split as to when this happens. GFS guidance
suggests that the front tries to move back south on Sunday,
while the European suggests the front stays to the north. So,
confidence in Sunday`s forecast is low and very dependent on if
the stationary front can stay out of the region. For now,
keeping chance PoPs in the forecast until guidance is a little
more clear on a solution. Temperatures on Saturday should warm
up to the low middle 80`s as the front lifts north. However,
Sunday`s temperatures will be dependent upon the progression of
the front.


Areas of low clouds and fog are possible overnight into early
Tuesday due to low-level moisture being trapped underneath the
nocturnal inversion. IFR conditions cannot be ruled out.

Any low clouds and fog should break early Tuesday morning with
VFR overall on Tuesday. Showers and storms are again expected
late Tuesday and Tuesday evening, however. Showers and storms
will remain possible on Wednesday as well, but low cigs are also
possible much of the day as the front drops back south across
the region.

With a stationary front lingering around the region Thursday
and Friday, it is likely that we will see clouds throughout that
entire period. Sub-VFR conditions could be possible at times
during the period. Scattered afternoon thunderstorms are also
possible during this period.


Strong to severe thunderstorms will clear the lower Tidal
Potomac River and middle portion of the Bay by 10 pm.

A Small Craft Advisory remains in effect through late this
evening for the middle portion of the Bay and the lower Tidal
Potomac River. The gradient will subside overnight so winds
should drop below SCA criteria.

More likely to have gusty winds across the waters much of
Tuesday as low pressure passes to our north. Storms again may
result in special marine advisories late Tuesday and Tuesday
evening. Winds probably relax a bit Wednesday, but showers and
storms will remain possible.

Despite all of the unsettled weather in the area on Thursday
and Friday, thanks to a stubborn stationary front and deep
southerly flow, winds look to remain below SCA criteria.
However, any thunderstorms that may form could create windy
conditions on the waters.


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.


MARINE...Small Craft Advisory from 6 AM Tuesday to midnight EDT Tuesday
     night for ANZ530>543.
     Small Craft Advisory until midnight EDT tonight for ANZ532>534-


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