Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 181731

Area Forecast Discussion
National Weather Service Blacksburg VA
1231 PM EST Wed Jan 18 2017

A cold front will move southeast to the coast by midday today.
Weak high pressure builds over tonight, then another storm
system moves over the southern Appalachians by Friday.


AS OF 1225 PM EST Wednesday...

Raised temperatures and high temperatures in the Piedmont this
afternoon. Adjusted cloud cover in the west for this afternoon
with cold advection. Increased winds and wind gusts for early
this afternoon. More changes later...

AS OF 918 AM EST Wednesday...

Modified temperatures with latest sfc obs and trended towards
GLAMP to capture warmer temperatures in the Piedmont with
downslope wind. Made a few minor adjustments in pops for this
morning. More changes later this morning...

AS OF 630 AM EST Wednesday...

Just a quick update to take pops out in the southeast, lower
cloud cover a little quicker lee of the Blue Ridge and bump
temps a few degrees warmer the next couple hours.

Previous forecast discussion...

Frontal boundary bisecting the forecast area this morning will
slide southeast to the Outer Banks of NC west-southwest to the Gulf
Coast states by early afternoon. Should see shower activity diminish
this morning and temperatures in the west will star to drop off. A
decent shortwave moves across the Central Appalachians into the mid-
Atlantic during the morning to midday. A brief period of strong
subsidence behind this will bring strong wind gusts to the higher
elevations from around dawn to early afternoon. At the moment should
stay under advisory level winds of 45 mph for gusts, though some of
the elevations above 4000 feet in the NC mountains and Grayson
Highlands should see some gusts to 45 to 55 mph for a few hours.
Will only mention in the HWO and possibly a Special Weather
Statement since coverage will not be great.

This shortwave and northwest flow will also increase the moisture
across the upslope side of the mountains in WV so keeping some pops
in through the morning. 8h temps sink to zero or below briefly
across the Alleghanys so some snow flakes possible in the Greenbrier

Going with a somewhat non-diurnal temperature forecast mainly in the
west where early morning temperatures still sitting in the upper 40s
to mid 50s. Temperatures should drop to the upper 30s to lower 40s
by the afternoon over WV with mid 40s to near 50 elsewhere west of
the Blue Ridge. The foothills/piedmont will be in the mid 50s to
lower 60s.

Sunshine will finally make a return to most of the area except the
mountains of WV.

Tonight skies will be mostly clear with some increase late in the
west of the high variety. Low temperatures as high pressure builds
overhead should be in the 30s, but still a bit above normal for most
areas for mid January.


As of 145 AM EST Wednesday...

This portion of the forecast will be characterized by a series of
upper level troughs that will progress northeast from the Four
Corners region northeast into the Central and High Plains states.
This scenario will keep our region within a mild, southwest flow
regime with impulses ejecting across our region from off the eastern
edges of the main upper troughs, all while tapping Gulf of Mexico

The exception to this rule will be on Thursday when a brief upper
level ridge swings trough the region bringing drier weather and more
sun than clouds.  Otherwise, Thursday night into Friday look for a
band of widespread light to moderate rain to overspread the region.
After a brief break Friday night into early Saturday, another round
of light to moderate rain is expected move into and across the area
late Saturday into Saturday night. For the most part, we will be
forecasting stratiform rain with these pseudo-warm front features as
they impact our region. The exception will be the western quarter of
the region Friday afternoon where rain showers are forecast.
Guidance is suggesting some weak surface based instability.

Temperatures will be on the mild side during this part of the
forecast, averaging around fifteen degrees above normal.


As of 330 PM EST Tuesday....

The main concern for the extended period is the potential for
significant precipitation, and to a lesser extent wind, in the
Sunday/Monday time frame. Guidance has been consistent with developing
a full latitude trof with a deep closed low over the deep south by
Sunday night. Persistent southerly flow will allow for efficient
moisture transport into the region and by Monday morning, precipitable
water values will be approaching 1.2 inches which is near record
territory for January. At the surface, occluded low pressure will be
moving up the Mississippi valley with a frontal boundary pushing in
from the west. With a very moist atmosphere, strong low level flow
parallel to thew baroclinic zone, and orographic effects from the Blue
Ridge, guidance begins to generate substantial rainfall on Sunday with
a continuation through Monday as the front moves through. These
parameters are consistent with heavy precipitation events, though we
are still out in the day 6/7 time frame and much of this, especially in
regards to timing and placement of heavy precipitation, is subject to
change with later model runs so the situation will be monitored
closely. Some embedded convection is also possible especially as the
front moves through Sunday night/Monday morning so this is another
aspect to watch in the days ahead. Lingering wrap around precipitation
will continue as the large system unwinds and pulls off to the north
early next week.


As of 1230 PM EST Wednesday...

MVFR SCT to BKN clouds will continue this afternoon into tonight
in the western taf sites of KBLF and KLWB. Gusty Northwest
winds will continue in the mountains, including Roanoke
this afternoon, then winds will trail off this evening into overnight
with high pressure building in. Some gusts could exceed 30 to 35 mph
early this afternoon. As high builds in tonight the lower cigs
at KBLF and KLWB should erode as well becoming scattered by
02z. VFR conditions will prevail after 02z and continue into

High confidence in ceilings,visibilities and winds during the
taf period.

Extended Aviation Discussion...

VFR conditions will continue into Thursday afternoon. However,
this is expected to be short-lived as moisture returns from the

Expect periods of rain Thursday night-Friday night, then again
Sunday into Monday. During this time expect sub-VFR cigs and at
times vsbys.




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