Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 211402
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1002 AM EDT Tue Mar 21 2017

.SYNOPSIS...
Weak high pressure will be over the region today. A cold front
will cross the area tonight into early Wednesday. High pressure
will return Wednesday through Thursday night. A warm front will
cross the region Friday. Low pressure may affect the area
Sunday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Plenty of stratus out there this morning with lingering low
level moisture and light north/northeast flow. Also seeing some
light rain/drizzle along and west of the Allegheny Front. As a
weak wave of low pressure passes by to our south and east, we`ll
see the low level flow turn more northwesterly which will allow
for some downsloping and that combined with increased mixing
should lead to some breaks in the cloud cover later this
afternoon. Temperatures therefore will be slow to warm this
morning, but should see a more marked increase later this
afternoon, with highs generally from around 60F for most
locations, with mid to upper 60s across central VA.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
While the wave of low pressure developing along the front to our
south will be too far away to affect us, there will be a second,
stronger cold front dropping into the area late tonight. Moisture
will be limited, although some guidance indicates a few light
showers may develop, with the best signal in central VA. There may
also be a brief period of upslope snow late tonight, but it too
should be light. Pressure surge behind the front will likely mean
wind gusts pick up noticeably even before the sun rises.

Strong cold advection behind the front will result in continued
breezy (25-35 mph gusts) conditions into the daytime of Wednesday
and temperatures that will be below normal. Highs may fail to reach
40 near the PA border, nudging to 50 in central VA, with 40s in the
remainder of the lower elevations. While high pressure will be
building in Wednesday night, it won`t be directly overhead, so there
will be some variance in decoupling. However, colder spots are
likely to dip into the teens with 20s elsewhere.

Sunny skies can be expected Thursday as the surface high crosses the
area. Temperatures will remain below normal though with most
locations in the 40s. Cloud cover increases Thursday night as
isentropic lift begins on the back side of the high. Most guidance
supports a dry night, although the ECMWF is notably quicker with
moving precipitation into the northwestern CWA. A light wintry mix
would be possible in this scenario since temperatures will likely
drop near or below freezing before clouds arrive.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Guidance remains in general agreement that a warm front will
advance across the region on Friday. The question is just how
fast and will there be any rain with it. Since this will be the
southeastern, tail end of the front, with forcing increasing
further north and west closer to low pressure, odds of any rain
will also increase as you go north and west. With warm air
advancing into the region, temperatures should turn out milder
with near-average readings expected, though with a noticeable
northeast to southwest gradient.

The high pressure which will bring our cool down Wednesday and
Thursday will settle off the Atlantic Seaboard later Friday and
Saturday, and with the warm front pushing north, winds will
become southwesterly. This same high, acting in conjunction
with an approaching low pressure from the west, will then act to
bring much milder air northward across the region for the
weekend. Widespread highs reaching the 70s for the first time
since March 9th are expected Saturday, with mostly dry
conditions as the storm continues to slow its approach in
guidance.

Mild conditions should continue Saturday night, then Sunday the
system approaches finally and we see an increasing chance of
showers. With temperatures remaining warm, there is a
possibilityof some thunder. This will need to be watched.

The low pressure slowly pushes across the region Sunday night
into Monday with some showers and temperatures dropping. With a
colder air mass close by, temperatures are uncertain, and it
could try to turn below normal once again.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
Some MVFR ceilings around this morning with stratus deck. These
will gradually lift and break during the late morning hours, and
VFR should be observed at all TAF sites by this afternoon.
Otherwise, light north/northeast winds this morning will become
northwesterly 5-10 kt as weak surface low slips southeast of
the area.

A strong cold front will push south through the area tonight.
Precipitation looks unlikely, but NW wind gusts will increase in its
wake with 20-30 kt gusts likely. These gusty winds will continue
much of Wednesday. Winds decrease Wednesday night into Thursday as
high pressure builds across the area.

Potential for sub-VFR cigs/vis exists Friday as showers may
cross the region, with best chance at MRB. VFR likely to prevail
Saturday.

&&

.MARINE...
Light/variable winds this morning will become northwesterly today
around 10 kt. A strong cold front crossing late tonight will
bring a surge of northwest winds of 20-30 kt. A brief period of
marginal gales late tonight to early Wednesday remains possible,
so will continue the mention in the HWO, but current guidance
doesn`t exude a solid enough signal to issue a warning at this
time. SCA conditions will continue into Wednesday evening at a
minimum.

Winds will be lighter Thursday into Thursday night as high pressure
builds across the area. Wind direction will become southerly by
Thursday night.SCA potential with a warm front passing on
Friday as a gusty southerly wind develops. Right now, it looks
like winds may subside a bit on Saturday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from midnight tonight to 6 PM EDT
     Wednesday for ANZ530>543.

&&

$$
SYNOPSIS...RCM
NEAR TERM...ADS/MM
SHORT TERM...ADS
LONG TERM...RCM
AVIATION...ADS/MM/RCM
MARINE...ADS/MM/RCM



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