Area Forecast Discussion
Issued by NWS Sterling, VA-- Remove Highlighting --
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FXUS61 KLWX 180236
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
936 PM EST Tue Jan 17 2017
A warm front will stall out across Maryland tonight. A weak cold
front will push through the area early Wednesday. High pressure
returns Thursday followed by an approaching warm front Friday.
High pressure returns again for Saturday. Low pressure will affect
the area to start the new week.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
-- Changed Discussion --The latest surface analysis (9pm) indicates that the warm front
has reached the Potomac River, evidenced by the sharp dewpoint
gradient in that vicinity, as well as light surface convergence.
Visibility across Maryland (north of the front) has sharply
dropped, with the development of fog. However, observations have
been wavering. Ultimately, have decided to place the northern
portion of the forecast area in a Dense Fog Advisory until 4am.
Visibility observations outright support this action in metro
Baltimore. For the rest of the Advisory area, believe that the low
clouds (200-300 feet) have enshrouded most of the hills in fog.
Still have a few showers crossing the area as well. The more
organized activity departed by dusk. What`s left is weakly forced
by overrunning. Am carrying chance PoPs to cover.
The associated weak cold front presently (9pm) is across West
Virginia. It will arrive during the overnight hours. Temperatures
will either remain steady or rise slightly up until the frontal
passage. Made those adjustments to the database earlier this
evening. The fropa will also provide enough drier air, not to
mention mixing, to break up any residual fog. Thus, expect fog to
largely be gone by daybreak.
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.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
Compact area of upper-level energy passes over the area
tomorrow...with spotty light rain chances mainly across the
Allegheny Front and along the Mason Dixon line. Elsewhere...expect
drying/warming conditions as high pressure builds into the region
through Thursday. Next system approaches late Thursday with
showers approaching our SW zones by early Friday. Highs Wednesday
and Thursday in the 50s.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
A storm system over the western Ohio Valley will pivot northeastward
into the Lower Great Lakes region Friday into Friday night. Some
energy associated with this main low will push across our region
during the same time. Light to moderate rain will gradually spread
northeastward across the Shenandoah Valley early Friday. Rain should
reach the District of Columbia and surrounding areas by Friday
afternoon. Temperatures will remain mild with high temperatures
about 10 degrees above normal. Drier air will work its way into our
region from the west behind this wave low pressure energy and
escorted by high pressure building in from the Ohio Valley.
Weak high pressure will be overhead Saturday into Saturday night.
Temperatures will stay mild throughout the period. A separate area
of high pressure over New England could aid in some cloud cover
with an upslope flow.
A storm system will develop over the Mississippi Valley and deepen
as it pivots northward Sunday and Sunday night. This low could send
additional energy into our region Sunday into Sunday night, bringing
the chance of rain showers once again.
On Monday, the main low will move northward into the eastern Great
Lakes. The threat for showers and perhaps a rumble of thunder exist
Monday. Temperatures will remain mild. Drier air will push in
behind the departing storm system Monday night.
High pressure will usher in cooler and dry air on Tuesday. Clouds
will breaking for sunshine, except for clouds and upslope rain
and/or snow showers in the Potomac Highlands possible.
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Flight conditions have been variable this evening. A warm front
stretches along the Potomac River, with IFR to LIFR north of the
front. CHO, on the other hand, has been VFR. Increasing fog
northeast of the front may result in further deteriorating
conditions until the arrival of a cold front. Anticipate the cold
front to reach the terminals after midnight but before dawn, with
improvement to come thereafter.
Mainly VFR tomorrow...though gusty NW winds up to 25 mph possible
in the wake of cold front.
IFR to LIFR conditions Friday with rain showers. MVFR conditions
Friday night. Winds southeast around 5 knots Friday. Winds light
and variable Friday night.
Primarily southerly sub-SCA winds expected through tonight.
However, with strong low-level wind field, may see some gusts
approach SCA-criteria this evening and tonight. Have continued
trend to keep winds just under Advisory criteria.
Winds will then turn to the northwest on Wednesday following cold
frontal passage. Gusts up to about 20 knots expected...a Small
Craft Advisory is in effect. Winds will then subside for
Wednesday night through Thursday night.
No marine hazards Friday through Friday night. Winds southeast
becoming light and variable 5 to 10 knots Friday through Friday
-- Changed Discussion --DC...None.
MD...Dense Fog Advisory until 4 AM EST Wednesday for MDZ003>006-011-
VA...Dense Fog Advisory until 4 AM EST Wednesday for VAZ028-031-505.
WV...Dense Fog Advisory until 4 AM EST Wednesday for WVZ050>053-504.
MARINE...Small Craft Advisory from 7 AM to 6 PM EST Wednesday for
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