Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 120154
Area Forecast Discussion
National Weather Service Blacksburg VA
854 PM EST Wed Jan 11 2017
A weak warm front to the northwest of the area will continue to
lift north and weaken overnight. Warmer southwest flow behind
this boundary will increase later tonight and continue into
Thursday. Another cold front will approach the region from the
north by Thursday night, before spilling south through the area
Friday into Friday night.
.NEAR TERM /THROUGH THURSDAY/...
-- Changed Discussion --As of 845 PM EST Wednesday...
Patchy earlier rainfall in advance of a warm front passing to
the west has exited the region this evening leaving a varying
degree of residual cloud cover in place. Latest evening
soundings show quite a bit more moisture than last night but
most forcing overnight looks to stay to the north/west of the
region. Thus have removed most lingering measurable rain chances
overnight with focus more on spotty drizzle along with
areas/patchy fog pending just how much of the strong jet aloft
can mix down. Latest short term guidance also showing less
cloudiness across the east overnight, so appears this likely
the region that could see more fog and eventually some stratus.
Otherwise mainly cloudy and a bit gusty at elevation under the
southwest jet aloft. Expect temps to remain about steady for a
while longer with some quick drops where clouds thin before
slowly rising later as warm advection deepens from above. Did
lower some spots espcly valleys where have dropped off into the
30s, and below previous forecast lows, with most likely to stay
in the 40s overnight.
Previous discussion as of 320 PM EST Wednesday...
Low pressure will move from the Midwest this afternoon into eastern
Canada tonight into Thursday and an upper ridge builds across the
Southeast States. The frontal boundary will stall this afternoon and
return fairly quickly as a warm front tonight. Rain associated with
the front will lift north this afternoon into evening back across
the northern parts of the CWA. The warm frontal associated rainfall
will then drift north into northern VA/WV overnight. For pops
initially started with blend of HRRR and HiResW-arw-east and trended
towards the Nam for tonight into Thursday.
Considerable cloudiness will persist with the low level waa pattern
and the cool moist ground. Deep low-level moisture across the area
will result in patches of drizzle and fog especially from the
Shenandoah Valley southwest into the New River Valley. Low
temperatures tonight will range from around 40 degrees in the
northern mountains to near 50 degrees in the far western mountains.
Our region will be in the southern stream of a split flow regime on
Thursday, with a large cutoff low over the southwest and flat
ridging over the Southeast. This will keep us in a mild and moist
pattern with cold air bottled up well to our north. With a weak
baroclinic zone just off to our west, isolated to scattered rain
showers are possible west of the Blue Ridge Thursday. High
temperatures Thursday will vary from the mid 50s in the mountains to
the lower 60s in the Piedmont.
-- End Changed Discussion --
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 334 PM EST Wednesday...
Cold front enters the mountains Thursday night. Best low level
convergence stays across the Central Appalachians and points west,
so will stay with drier scenario per model blend east of the Blue
Ridge with high chance to low likely over Southeast WV to the Clinch
River Valley of Southwest Virginia. With front crossing the Blue
Ridge late, should see temperatures stay relatively steady Thursday
night and mild, with lows actually expected to be warmer than what
are normal high temperatures are for mid-January, in the upper 40s
to lower 50s. We may see some record warm low temperatures broken.
Friday, the front slides southeast to NC with a wave of low pressure
tracking along it from leading to an increase in chances of rain.
Should be a cooler day as wind flow turns more northwest yet light,
with cloudy skies. However, temperatures starting out in the upper
40s to lower 50s may surge up enough about 5 to 15 degrees before it
rains, especially in the piedmont to have highs range from the lower
50s out in WV to mid 60s southside VA to the NC foothills. Could see
a bust if the front is slower or faster and less or more rain occurs
Friday night-Saturday becomes tricky in terms of strength of high as
cold air damming sets up lee of the Appalachians. The 1046 high over
the Great Lakes Friday evening, crosses to New England by Saturday
morning slightly weakening. Low pressure over the TN valley starts to
lift northward bringing overrunning setup across the area with best
coverage across WV and the Alleghany Highlands Friday night into
early Saturday. Setup is such that cooler northeast to east flow
will send temperatures to around freezing overnight Friday night
into Saturday especially along the Blue Ridge north of
Floyd/Roanoke/Bent Mountain, northwest to the Alleghanys in Craig
County north to Bath. Warm nose aloft suggests more a freezing rain
vs rain scenario though further north column may cool enough for
sleet. At the moment too early for any headlines but will highlight
in the HWO icing threat for the Blue Ridge and Alleghanys late
Friday night into Saturday. Rest of the forecast area will see rain
with best chances across the mountains. Temperatures Saturday
southwest of the wedge will warm into the lower 50s, i.e. Chilhowie
and Richlands, while most stay in the 40s, except cooler across the
Blue Ridge north of Roanoke and the eastern slopes of the Alleghanys
north of New Castle, VA.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
.AS OF 334 PM EST Wednesday...
Amplified southern stream to take shape Sunday into next week with 2-
3 systems moving from the desert SW northward/northeastward to the
upper MS Valley. Will start to see the cold air damming setup weaken
by Sunday with frontal boundary over us weakening. Will still be on
the cloudier side at times, but at the moment Monday looks like the
driest day with highs in the 50s. Will see frontal boundary approach
midweek with southwest flow increasing aloft keeping temperatures
well above normal. Will see some showers scattered around Tuesday
with better chance Wed-Wed night as the front tracks west of the
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
As of 555 PM EST Wednesday...
Overall outside of the exiting rain/drizzle near KLWB,
conditions have briefly improved to VFR for early this evening.
However a warm front will lift north across the region tonight
resulting in another round of strong southwest winds aloft as
the jet increases to around 50 kts overnight. This will again
result in areas of low level wind shear espcly this evening so
included a LLWS mention in most spots excluding KBLF where
should see stronger surface winds.
As the front moves north of the region a moist air mass will be
left in place over some snow covered ground tonight into
Thursday morning. Expect widespread fog and drizzle to develop
as a result with attendant IFR-LIFR conditions at most TAF sites
by midnight, then continuing through the remainder of the
night. Latest ensemble HREF has the most widespread dense fog
developing out east so expecting the lower vsbys and cigs to
take shape there where more snow remains. Look for cigs and
vsbys to rise Thursday morning with most locations returning to
VFR during the afternoon.
Winds will remain light in most areas overnight as the jet aloft
skims across the top of the inversion and perhaps mixes down
along the ridges from time to time. Southwest winds should
increase as deeper warm air arrives Thursday with speeds at 10
to 20 kts including gusts perhaps to 30 kts Thursday afternoon.
Medium to low confidence in ceilings, visibilities and winds
through the valid TAF period.
Extended Aviation Discussion...
Little to no improvement is expected through the period. A
backdoor frontal system will work its way south into the region
Friday into Saturday, maintaining the threat for additional sub-
VFR in low cigs along with light rain and/or drizzle. Unsettled
weather will continue into Sunday with some slow improvement in
conditions as high pressure wedges in from the north, but
likely still MVFR cigs at best. Southerly flow will develop
Monday ahead of a frontal system in the Central Plains with
periods of MVFR possible mainly west where a few showers may