Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 210801
AFDLWX

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

.SYNOPSIS...
A weak high pressure will envelop the region today. A cold
front will cross the area tonight. 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/...
A weak upper level disturbance is currently crossing the area. While
showers are quite numerous, they are very light and will result in
less than a tenth inch of rain. A weak surface low is located in
southwest West Virginia. Convective remnants ahead of this low may
skirt Highland to Nelson Counties through daybreak. After these
showers move out and/or dissipate, only some light upslope rain
showers or drizzle will occur through the rest of the morning.

Light northwest flow will ensue for the afternoon as the weak low
pulls a front into the Carolinas. Clouds will likely be slow to
break, but there will be some glimpses of the sun in the afternoon.
These breaks should be enough to allow temperatures to rise into the
60s for much of the area.

&&

.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 conjuction 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 possiblity
of 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 /08Z TUESDAY THROUGH SATURDAY/...
Showers associated with a weak disturbance should be pushing away
from the terminals by 09Z. Guidance indicates low clouds are
unlikely this morning, although lower VFR cigs could occur through
midday or so. Otherwise, winds will become northwesterly 5-10 kt as
a front slips south 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 as a weak front slips south of the area. A stronger
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
SHORT TERM...ADS
LONG TERM...RCM
AVIATION...ADS/RCM
MARINE...ADS/RCM



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