Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 100900

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
400 AM EST Tue Jan 10 2017

A warm front will gradually approach from the south today and
tonight as high pressure slides east off the coast and a storm
system passes to the northwest Wednesday. The warm front will
cross the region Wednesday. A cold front will then drop back south
across the region Thursday night into Friday. The front will stall
to the south and a wave of low pressure will ride east along the
front this weekend.


High pressure is centered along the eastern seaboard, however mid
and high level clouds are quickly approaching from the west, so
expect a mostly cloudy to cloudy day. A lobe of vorticity is
producing a band of light snow in the upper Ohio Valley, although
obs suggest it is virga south of I-70. Have some low end POPs for
northwestern parts of the area through the morning, but would expect
little to no accumulation with dry low levels. It`s not totally out
of the question a flurry could reach the DC/Baltimore area, but it
appears the band should be dissipating as it crosses the area.

Otherwise, the remainder of the day should be dry in most areas.
It`s possible the second band of precipitation currently near the
Ohio/Indiana border could scrape the far NW CWA this afternoon,
which would have a better chance of being mixed precipitation due to
warming profiles (if anything occurs. Temperatures should warm some
today with a steady southerly wind, but the cloud cover will not
help in eroding the dense Arctic air. Have highs in the 30s...with
hopes most areas rise above freezing by mid-late afternoon.

A shot of isentropic lift/PVA will approach early this evening ahead
of a cold front moving into the Ohio Valley. Precipitation will
spread eastward into the area, with the greatest coverage in the
northern and eventually eastern parts of the area. By this time,
temperatures aloft will have warmed enough for liquid hydrometeors.
However, there is some signal in model data that some pockets of
subfreezing air could still exist...mainly near the PA border and in
Highland County, whether due to evaporative cooling or the cold air
never being scoured out. In addition, pavement temperatures are
currently in the teens and it is uncertain how quickly they will be
able to recover without sun today (i.e. we could have ice form even
if thermometers are reading 33 or higher). Would not be surprised if
a Freezing Rain Advisory is needed for a brief period this evening,
but in coordination with neighboring offices, will hold off on
issuing for now due to uncertainty in the extent of subfreezing
temperatures and timing of precipitation.

The area of rain will push off to the east by daybreak. Temperatures
should hold steady or slowly rise through the night. Fog may develop
as warmer moist air moves over the cold ground.



The cold front will basically fall apart over the area on Wednesday
as it becomes parallel to the upper flow. The pressure gradient will
weaken so winds will be light and clouds and possibly fog are
expected to persist. Have therefore cut back some on high
temperatures, to the upper 40s to lower 50s. The next low level jet
induced batch of rain will approach during the afternoon and move
across the area through the evening. Expect low clouds and possibly
fog to linger after the rain ends. Lows will stay in the
40s...perhaps some upper 30s.

The wave from Wednesday night will help lift the front back to the
north on Thursday. It appears we will get into better southerly
flow, and it`s even possible the clouds could thin a bit. Thus
Thursday will be the warmest day this week with highs potentially
into the 60s. Meanwhile low pressure will be passing by to our
north, with some guidance indicating the associated cold front will
sink south into the area by late Thursday night. At this time, it
appears most precipitation will be confined to the western slopes of
the Appalachians.


Front slips south on Friday with perhaps some showers accompanying
it as gusty northwest wind ushers in colder air. Wedge looks to
get stuck across the region over the weekend as high pressure sits
to the northeast. This spells potential trouble as a wave of low
pressure rides eastward Saturday and Sunday, bringing rain and
possibly some ice or snow. Temps will be tricky but wedge
scenarios always tend to run colder than progged. Temps look to
gradually warm early next week as low pressure rides northward to
our west.


Mid and high clouds dominate today ahead of Great Lakes low
pressure. A disturbance could produce some flurries at MRB this
morning but confidence is low. Southerly winds could gust to 20 kt
at times.

A weakening cold front drops toward the area tonight. Precipitation
spread in during the mid to late evening. At this time it appears to
be rain at the terminals, but will need to watch surface
temperatures (mainly MRB) for ice potential. Conditions will also
drop to MVFR and possibly IFR by late tonight, even though any rain
should end by daybreak.

Low clouds and fog may persist through Wednesday as light winds
don`t mix the airmass. The next batch of rain will arrive Wednesday
afternoon into evening with continued sub-VFR conditions. IFR
cigs/vsbys could linger into Thursday morning. However improvement
to VFR is possible later in the day with gust southerly winds.

Sub-VFR possible Friday thru the weekend as front settles back
south and low pressure rides east. Potential for low cigs and vis
in rain, and possibly some ice and snow Friday night into Sunday.


Southerly flow over the waters this morning and will likely persist
through the middle of the week without any strong frontal passages.
SCA goes into effect for all waters this morning, although the start
time may be a little early for some locations. However, already have
some gusts in the 15 kt range. Think strong winds persist through
the evening until a batch of rain moves through. Will have the SCA
tapering down from NW to SE between 3 and 10 AM Wednesday.

There will be a lull in winds Wednesday, but flow will strengthen
again, especially by Thursday when good mixing should promote SCA
conditions. Fog may also develop from late tonight through Wednesday

Small craft potential with gusty NW winds behind the cold front on
Friday. Winds look to diminish over the weekend as front stalls in
the area.


MARINE...Small Craft Advisory from 8 AM this morning to 6 AM EST
     Wednesday for ANZ530-531-538-539.
     Small Craft Advisory from 8 AM this morning to 10 AM EST
     Wednesday for ANZ532>534-537-540>543.
     Small Craft Advisory from 8 AM this morning to 3 AM EST
     Wednesday for ANZ535-536.


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