Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 130209

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

A cold 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.


As of 02z, a cold front stretches from near Caribou, through
central Pennsylvania, to near Charleston WV. Showers and
thunderstorms from this afternoon along the front have weakened,
but a solid line has held together as they approach the forecast
area. Some leading showers have entered northern Maryland and
adjacent eastern West Virginia; have updated forecast to account
for scattered showers north of DC through the evening. Guidance
still predicts the line will fall apart before entering the area
further, which is accepted given the loss of feeble January
daytime heating.

Temperatures still in the mid 60s. In light of this, have adjusted
hourly temperatures, and thus low temperatures, upward. Lows will
be warmer than normal highs for this date.

Strong high pressure (1040mb+) will 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 conditions ahead of a cold front. As frontal boundary moves
across the region between midnight and dawn, may see a brief
period of MVFR ceilings. Like predecessor, have left out of TAFs
due to expected limited coverage and uncertainty. 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 tonight with Small Craft Advisory in
effect. 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.


Two record daily high temperatures were set for January 12th:
70 degrees at BWI (ties record for Baltimore area from 1890)
70 degrees at IAD (breaks record of 63 set in 1995)

Record daily warm low temperatures are possible for January 12th:
DCA (DC area) record is 47 set in 1890
BWI (Baltimore area) record is 46 set in 1890
IAD (Dulles area) record is 41 set in 2013

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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