Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 111343
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
943 AM EDT Wed Oct 11 2017

.SYNOPSIS...
A frontal zone will remain nearly stationary across
the Mid-Atlantic through this evening. An area of low pressure
will track along the front tonight and push it to our south and
east late tonight into Thursday. High pressure will build north
and east of the area later Friday through Saturday before
moving offshore Sunday. A stronger cold front will pass through
the area early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A nearly stationary boundary remains over the Potomac Highlands
into central Virginia today. The boundary separates cooler
marine air to the north and east vs. warm and humid air to the
south and west. The boundary will remain nearly stationary over
the area today...but shortwave energy will pass by to our north
this afternoon. This will cause the low-level boundary between
925-850mb to move north and east as a warm front. Thus...warm
and moist air will be overrunning the surface cooler air in
place and the added lift from the low-level boundary will cause
showers throughout the day along with plenty of clouds. Will
continue to the slight chance for thunder across the Potomac
Highlands into central Virginia and southern Maryland...closer
and to the south of the surface boundary. PWATS over 2 inches in
spots will cause rain to be moderate to locally heavy at times.
As of now...any flood threat is low due to recent dry
conditions preceding the rainfall.

Max temps will range from the 60s across northern Maryland...to
the lower and middle 70s near Washington and Baltimore...to the
upper 70s and lower 80s across portions of central Virginia.

More shortwave energy will pass by to the north tonight while
the surface boundary remains nearly stationary overhead. More
showers are expected across the area along with possible
thunderstorms to the south and west of the boundary across
central Virginia into the Potomac Highlands and southern
Maryland. The shortwave energy will move off to the east
overnight and the surface boundary will drop south and west as a
cold front. The onshore flow will cause low clouds along with
areas of rain and drizzle/fog overnight.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
The pattern through the end of the week (Thursday and Friday) will
be similar, marked by east/northeasterly flow around building high
pressure over New England. Model guidance exhibiting a pattern of
cold air damming, with light precipitation lingering along the Mid
Atlantic. Forecast will be for ample clouds, chance of rain,
areas of drizzle, and patchy fog. The mountains will be
preferred for precipitation due to upslope, but chances reside
just about everywhere. Temperatures will be substantially
cooler, likely struggling to reach 70 degrees during the day,
and staying near the dewpoints (in the 50s) at night.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
A strong mid-upper level ridge will remain anchored to the
south on Saturday with a return to above normal temperatures on
Sat after a couple of cool days Thu and Fri. The ridge will be
pushed to the east Sunday as a shortwave-trough and associated
cdfnt move across the Great Lks region Sun night. There could be
a few showers Sun night with the frontal passage but the
westerly sfc wind trajectories ahead of the front and lack of
instability at night suggest any rainfall will be very light at
best. The trof axis will move across the area Mon night with a
taste of fall weather middle of next week as sfc high pressure
builds in from the northern Rockies.

&&

.AVIATION /13Z WEDNESDAY THROUGH SUNDAY/...
A stationary boundary will remain to the south and west of all
the terminals except KCHO through this evening. An easterly flow
to the north and east of the boundary will cause low clouds
along with occasional showers. MVFR to IFR conditions are
most likely. Timing of IFR conditions still remain uncertain as
of now. For KCHO...low clouds this morning may break this
afternoon behind the stationary boundary. However...a few
showers and even a thunderstorm are likely into this evening and
this will cause restrictions at times.

The boundary will drop south and west as a cold front late
tonight. An onshore flow behind the boundary will cause more
low clouds and some fog along with areas of rain and drizzle.
MVFR-IFR likely to linger for a majority of the time through
the remainder of the week with a real taste of fall weather for
the middle of next week.

Cdfnt will be crossing the area late Sun night and early Mon
with only a few showers but no flying restrictions anticipated
at this time.

&&

.MARINE...
An onshore flow will persist across the waters through this
evening. A Small Craft Advisory is in effect for the middle
portion of the Bay and lower Tidal Potomac into this afternoon.
There may be a break in the winds later this afternoon and
evening...but onshore winds should be increasing this later
tonight. A Small Craft Advisory in effect for the Bay and lower
tidal Potomac after midnight, and have extended it through
Thursday. It likely will need to be extended further.

Small craft advzy conditions likely Sun into Tue with a small
chance of gale conditions Mon night due to cold air advection
over warm water.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies have already begun to increase due to the
onshore flow. The onshore flow will continue through late this
week and this will cause water levels to increase. Minor tidal
flooding is possible with the high tide cycle this evening
across St George Island. Chances for minor flooding will
increase across all locations Thursday through Friday.

&&

.EQUIPMENT...
The NWS 88D Sterling radar (KLWX) will be down during the day
from 7 AM through 5 PM today through Saturday this week. This
is for nationally scheduled maintenance on the radome. Our
surrounding 88D radars as well as FAA terminal radars will
continue to scan our skies during this downtime.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from midnight tonight to 6 PM EDT
     Thursday for ANZ530>534-537-539>541-543.
     Small Craft Advisory until 3 PM EDT this afternoon for ANZ533-
     534-537-541>543.

&&

$$
SYNOPSIS...LFR
NEAR TERM...BJL/HTS
SHORT TERM...HTS
LONG TERM...LFR
AVIATION...BJL/LFR/HTS
MARINE...BJL/LFR/HTS
TIDES/COASTAL FLOODING...BJL/HTS
EQUIPMENT...BJL



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