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FXUS61 KRNK 172030

Area Forecast Discussion
National Weather Service Blacksburg VA
330 PM EST Tue Jan 17 2017

A cold front will track into the mountains this evening, then move 
southeast to the coast by Wednesday morning. Weak high pressure 
builds over by late Wednesday, then another storm system moves over 
the southern Appalachians by Friday. 


AS of 327 pM EST Tuesday...

A cold front to our west across central Kentucky and Tennessee this 
afternoon will east this afternoon and moves southeast through the 
forecast area tonight into Wednesday. An isolated thunderstorm may 
be possible over the Mountain Empire and northwest mountains of 
North Carolina with some instabilities this afternoon into tonight.
However, not expecting to much thunder because of cloud cover and 

The HiResw-arw-east, HRRR, RAP and NAM support placing the highest 
pops in the west this evening into Tonight. The GFS and ECMWF seem 
to develop an area of deeper convection east or southeast of our 
forecast area. The shortwave rotating through Southeast West 
Virginia supports likely pops in the west, with chance pops to the 
east. It will remain mild tonight with readings from the upper 30s 
in the northwest mountains to the mid 50s in the Piedmont. 

Increased winds speed late tonight into Wednesday morning. From 
Grayson county Virginia south through portions of the Northwest 
mountains of North Carolina, winds will approach wind adv levels for 
a small window around 12z. Because of limited areal coverage and 
time coverage with lagging CAA will hold off on any wind adv 
headlines.  The northern-stream trough exits Wednesday morning,then 
a ridge builds in from the west Wednesday afternoon. High pressure 
will build southeast out of the Ohio Valley. High temperatures 
Wednesday will vary from around 40 degrees in northwest Greenbrier 
county to the lower 60s in the Piedmont.  


As of 330 PM EST Tuesday....

As a large cutoff traverses the southern plains, the ridge over the 
eastern US will amplify and bring quiet weather to the region through 
Thursday as high pressure settles over the Appalachians and central mid 
Atlantic. In fact, Thursday looks to offer the first good glimpse of 
the sun for most of the region in a few days. However, this reprieve 
will be short lived. By Thursday night the ridge axis will move to our 
east, leaving behind a lingering wedge of high pressure, and the closed 
low to our west becomes a progressive open wave. This will allow a 
surge in isentropic lift and vigorous dynamic support to accompany a 
frontal passage late Thursday night/early Friday with a good chance of 
rain. By late Friday the front any dynamic support will be pulling out 
of the area and bring an end to widespread precipitation.

There will be no appreciable change of airmass so temperatures will 
remain above normal through the end of the week.


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 1245 PM EST Tuesday...

Poor flying conditions this afternoon into Wednesday with 
rapidly changing conditions and widespread reduction with low 
clouds,rain and fog. MVFR ceilings with scattered IFR and LIFR 
in rain and fog. A cold front expected to get into the 
mountains this evening, and main focus for showers will be from 
the ROA/BCB areas west to BLF/LWB and at times LYH with DAN with
lower threat. Some instability may sneak into the mountains of
Southwest VA southwest of BLF this afternoon into this evening 
bring an isolated thunderstorm. Showers should start to taper 
off later this afternoon/evening in the ROA/LYH/BCB area and 
south, while keeping it showery into tonight at BLF/LWB per 
upper level support with front. Lower confidence in ceilings 
and visibilities overnight. At the moment expect enough wind to
keep most places no worse than MVFR, except the BLF airport 
which is more elevated and cigs will be around 1kft. Clearing 
will take place behind the front on Wednesday. Conditions will
become VFR Wednesday afternoon into early Thursday. Southwest
winds will increase in speed this afternoon into tonight. A cold
front will then cross the region tonight into early Wednesday 
with a turn to northwest winds. Winds will gust up to around 25 
knots by Wednesday afternoon.

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

Extended Aviation Discussion...

VFR conditions will prevail Wednesday afternoon into Thursday. 
However, this is expected to be short-lived per return of 
unsettled weather by weeks end as moisture returns from the 
southwest. No precipitation type issues are expected through the
end of this week...just plain ole rain. However, IFR conditions
may be possible in rain Thursday night into Sunday.





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