Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 121836

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
136 PM EST Thu Jan 12 2017

A cold front will approach from the northwest today. The front
will cross the region early Friday. The front will stall to the
south and a few waves of low pressure will ride eastward along the
front over the weekend into early next week.


Deep southwest flow is in place across the region this afternoon
ahead of an approaching cold front from the northwest. Seeing
partly to mostly cloudy skies with breaks of sun in the high
clouds aloft. Temperatures have responded nicely with widespread
60s to near 70F out there right now. Will see these rise a few
more degrees with highs in the upper 60s to low 70s.

Cold front will then progress southeastward towards the region
tonight, crossing between midnight and sunrise Friday morning.
Precip associated with the front will be lessening as it
approaches, so showers likely across the higher terrain and in
western areas, with only a few light showers possible (20%) as it
crosses the rest of the region. After a very mild evening,
temperatures will drop post-front, with 40s to low 50s by morning
from north to south. Before the front, may be a few patchy areas
of fog, but winds should preclude more widespread development.

Strong high pressure (1040mb+) will then build into the Great
Lakes eastward to New England on Friday and Friday evening. This
will induce low level northerly flow. Still expecting plenty of
high clouds with baroclinic zone nearby. Highs mid 40s to mid 50s.


Waves of moisture will then move towards the region along the
stalled frontal boundary that will be positioned to the south
Friday night. As surface high holds over New England through
Sunday, will see continual northerly surface flow with cold air
damming, feeding in low level cold air into the region. This will
set the stage for a prolonged light mixed precip event from Friday
night through Saturday, and into Sunday morning.

Most widespread and organized area of precip will overspread the
region after midnight from west to east Friday night,
encompassing the entire area during the Saturday morning hours.
Forecast is highly temperature dependent with low level cold air
funneling in from the north with weak warm air advection occurring
aloft. General trend should be a start with light snow/sleet,
transitioning over to sleet/freezing rain from southwest to
northeast. By Saturday afternoon/evening, precipitation should
generally have tapered off to a either a very light
sleet/freezing rain (possibly some snow north) or drizzle/freezing
drizzle. This very light precip is expected to continue through
Saturday night and into Sunday morning. While event will be long
in duration, precip amounts will be light, and precip is not
expected to be falling continually during entire timeframe.

Total snow/sleet amounts expected to be a dusting to less than
one inch for most locations, except around one inch or slightly
higher where snow can hang on the longest across northern Maryland
and West Virginia. Ice accumulations will be a trace to a tenth of
an inch for most of the area, with one to two tenths possible
possible across portions of western Maryland and down into
portions of West Virginia, especially along the Allegheny Front.
There is some concern for higher precipitation amounts due to
upslope flow in these areas, but have held off on Winter Storm
Watch for now due to uncertainty. Lowest snow/ice threat from
central VA and into southern MD.


Strong high pressure centers over the Great Lakes on Sunday while
a stationary front stalls to our south, setting northerly flow
over our region. Precipitation is possible near the front as it
pushes south, which could bring precipitation to our region, but
guidance is not in agreement in p-types... and even if we will
have any precipitation at all.

The front will lift north as a warm front late on Sunday or Monday
with winds becoming southerly behind it and upper level ridging
building in. Another warming trend is expected Tuesday into
Wednesday with high temperatures reaching the 50s and 60s. A cold
front approaches from the west and weakens over our area, followed
by a low pressure system that will push northeast from the Gulf
states increasing the PoPs sometime Wednesday night into Thursday.


VFR through the rest of today with gusty southwest winds and high
clouds. As frontal boundary moves across the region later tonight
and early Friday morning, may see a brief period of MVFR ceilings,
but have left out of TAFs for now due to expected limited coverage
and uncertainty. There may also be a few areas of patchy fog
before the frontal passage, but winds should limit coverage. As
front passes, winds will turn to the north.

Front will stall south of the region Friday through Sunday with
light northerly flow expected to continue. VFR expected Friday,
but lower sub-VFR ceilings/visibilities likely developing later
Friday night and through at least Saturday night with areas of
light mixed precip and icing concerns.

Sub-VFR conditions possible as frontal boundary stalls near our
area Sunday, bringing some precipitation with it. Wintry mix
possible early in the day but details are still uncertain. The
front lifts north late Sunday into Monday and dry conditions
follow behind it into Tuesday.


Gusty southwest winds continue today and this evening with Small
Craft Advisory in effect. A few gusts nearing Gale are possible,
but will be brief and isolated. Winds weaken and turn northerly
overnight and into early Friday morning as front crosses the
region. Another Small Craft Advisory is in effect on Friday for
all waters and into Friday night for the lower Chesapeake and
Potomac as northerly winds increase behind the front.

Sub-SCA conditions will then return later Friday night through at
least Saturday night.

Frontal boundary stalls near our area Sunday, bringing some
precipitation with it. Wintry mix possible early in the day but
details are still uncertain. The front lifts north late Sunday
into Monday and dry conditions follow behind it into Tuesday.
Winds will be light, so not expecting small craft advisory
conditions Sunday into Tuesday.


MARINE...Small Craft Advisory until 3 AM EST Friday for ANZ530>534-
     Small Craft Advisory from 8 AM to 6 PM EST Friday for
     Small Craft Advisory until 10 PM EST this evening for ANZ535-
     Small Craft Advisory from 8 AM Friday to 1 AM EST Saturday for


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