Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
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FXUS61 KRNK 182317
Area Forecast Discussion
National Weather Service Blacksburg VA
717 PM EDT Sat Mar 18 2017
An upper level area of low pressure and its associated cold
front will cross the region from the west this evening before
exiting overnight. High pressure will then follow the front for
Sunday and Monday. A series of cold fronts will drop south
across the area Tuesday into Wednesday with additional rounds of
.NEAR TERM /THROUGH SUNDAY/...
As of 625 PM EDT Saturday...
Forecast on track, had some thunderstorms with sub-severe hail
across the piedmont/foothills, and even over portions of the
Roanoke and New River valley since 3pm. The strongest convection
has now exited Halifax County. Cold front now lined up near the
Blue Ridge as evidenced by a northwest shift in winds at Roanoke
with gusts to 34kts.
Will still see some limited thunder/hail threat in the east til
about 8pm, while in the mountains we start to see some cold air
moving into the mountains with rain changing to snow showers
across the Greenbrier/Bath county higher terrain by 8pm.
Winds with this initial fropa surge may gust as high as 45 mph,
mainly in the higher elevations/foothills, but overall stay
below advisory levels except possibly in elevations above 4000
ft in NC. No advisory planned.
Previous discussion from early afternoon...
Cold front still just west of the mountains should finally push east
across the area this evening before exiting overnight. Already
seeing clusters of mainly small hail producing convection due to
cold air aloft, and expect this coverage to increase/organize a
bit more upon heading east of the mountains over the next few
hours despite only weak surface based instability. This in line
with the latest HRRR and Rap solutions so running with highest
chance pops eastern half into early this evening. 850 mb front
beneath the passing strong mid level shortwave trough will
follow the surface front across the mountains by sunset and work
through the rest of the area this evening. This will cause
northwest winds to quickly increase as well as deeper cold
advection as the nose of the jet aloft punches in. However
latest local scheme numbers suggest that winds, other than for
a surge with the front, will overall stay below advisory levels
given a 40ish knot jet under a rather steep inversion without
really cold air as seen in past events. Thus pushed gusts to
just below criteria southern Blue Ridge where best subsidence
will reside overnight. Otherwise should see clearing develop
east of the mountains this evening/overnight while upslope snow
showers kick in out west where an inch or two of snow looks
possible through Sunday morning. Kept lows on the warmer side of
guidance, mostly 30s, given mixing beneath a not overly cold
Upper cold pool will be slow to depart on Sunday with the core of
the mid level shortwave energy not exiting to the southeast until
Sunday afternoon. This in conjunction with high pressure building in
from the west may keep more of a northerly flow in place espcly east
where clouds could linger piedmont from late tonight through
midday Sunday. However this along with dry air/subsidence should
also tend to shutoff the upslope snow showers by midday if not
sooner, with mainly sunny skies in between early on. Expect all
except the far northwest to finally clear out during Sunday
afternoon with winds diminishing a bit as the pressure gradient
starts to weaken, but still quite blustery. High temps under
the cold pool likely to struggle in the 40s to near 50
mountains, while recovering into the mid/upper 50s east given
aid of downslope drying and warming of dry air.
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 230 PM EDT Saturday...
High pressure builds overhead in the wake of the exiting upper cold
pool Sunday night before sliding to the south Monday in advance of
the next upstream cold front. This will make for another cold Sunday
night with lows in the 20s to lower 30s under good radiational
cooling. Warmer air quickly returns Monday under westerly flow aloft
and 850 mb temps jumping to near +10C by the end of the day.
This combined with sunshine and clouds not increasing until
afternoon supports highs mostly in the upper 50s to mid 60s
with any isolated showers holding off across the far northwest
until late. Deepening moisture/clouds continue to increase
Monday night with added shower bands arriving across the western
sections espcly after midnight. Otherwise mainly dry out east
under strong downsloping flow aloft and better moisture
convergence stuck over the far west. Should be milder under
warming aloft and mixing with lows mostly in the 40s.
Front will drift into the area Tuesday and perhaps linger southern
sections Tuesday night before finally getting shoved to the south
via passing stronger shortwave energy to the north on Wednesday.
This scenario remains uncertain with guidance showing a possible
weak wave along the boundary by Tuesday night which could result in
more widespread precip into early Wednesday. Exactly where/if low
pressure develops key to pops Tuesday afternoon into Wednesday with
some solutions farther south and others leaving moisture around with
colder air bleeding in from the north at the end. For now will
continue mostly chance pops except a period of likelys late Tuesday
into Tuesday night mainly southern/eastern half including some light
snow far northwest toward daybreak Wednesday as deeper cold
advection arrives. Models also indicate quite a bit of instability
over the far southern sections late Tuesday so including a thunder
mention there as well. Should finally see decreasing clouds from
north to south by Wednesday afternoon but cooler with highs mainly
40s north/west to 50s elsewhere after a rather mild Tuesday.
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 1245 PM EDT Saturday...
Shortwave ridging will strengthen over the region later next week in
the wake of a passing cold front to the south by Wednesday night.
This will give rise to strong high pressure building southeast
across the Great Lakes before wedging south down the Mid-Atlantic
coast Thursday into Thursday night. However models remain uncertain
in just how strong the wedge will be espcly in regards to low level
moisture and subsequent low clouds. At this point appears the dry
wedging wont be strong enough to scour out clouds along the southern
Blue Ridge, but could see more clearing elsewhere given the closer
proximity of the parent high just to the north. Otherwise will be
chilly but dry into Thursday night. High then slides offshore later
Thursday night allowing a weak warm front to shift north on Friday,
in turn scouring the wedge under rebounding temps to more seasonal
levels. Next round of shortwave energy heads out of the Rockies by
the end of the week with an associated cold front approaching by
next weekend. Timing of this boundary into the eastern ridging
remains iffy but appears enough return of deep moisture to warrant a
chance of showers mainly Saturday afternoon and overnight. Should
also be all liquid with temps well above normal by Day7.
.AVIATION /23Z SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --As of 712 PM EDT Saturday...
Looking at drying conditions east of the mountains this evening
with cold front pushing across and out of the piedmont by 01z.
Will see gusty winds across the mountains/foothills early on,
with some gusts over 35 kts near TNB-HSP, but a little less at
the taf sites. Should start to see some lower cigs working into
BLF/LWB after 03z, with rain or snow showers starting up after
06z, changing to all snow showers by 09z. Appears most of the
snow will be west or northwest of LWB/BLF so have no limited
Northerly flow will work in Sunday with cigs rising to VFR in
the mountains by 12-15z. Not out of the question from LYH/DAN to
have some mid/high clouds Sunday but nothing to affect aviation.
Extended Aviation Discussion...
High pressure building in on Monday should yield VFR all
terminals to start the week. However moisture ahead of another
cold front and associated weak low pressure may arrive by Monday
night, with sub-VFR possible later Monday night mountains and
all areas Tuesday into Tuesday night before improving
conditions back to VFR take shape during Wednesday.
By Thursday high pressure will wedge in from the northeast so
will stay VFR though increasing clouds are expected by
afternoon, but should stay VFR.
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