Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 161740
Area Forecast Discussion
National Weather Service Blacksburg VA
1240 PM EST Thu Feb 16 2017
Low pressure was along the New England Coast, with High pressure
centered over the Lower Mississippi Valley. Pressure gradient
between these two features will result in blustery cool
conditions today. The area of high pressure will drift overhead
tonight, winds diminishing. An area of low pressure will move
across South Texas Friday, then across the Southeast and into
the southern Appalachians this weekend with scattered rain
.NEAR TERM /THROUGH FRIDAY/...
As of 933 AM EST Thursday...Just small cosmetic changes to the
grids, increasing sky cover slightly along and downwind of the
Alleghany and Blue Ridge Mtns as morning visible depicts streets
of mountain wave clouds. Additional areas of cloud cover
associated with upslope flow in northern Bath, Alleghany VA into
Greenbrier County, as well as in the OVC low-to-mid cloud layer
associated with weak isentropic lift extending into Smyth and
Tazewell County and into the eastern KY/TN/WV area. I also
raised dewpoints a bit over the VA Southside into the NC
piedmont over the next couple hrs.
Should still be a relatively breezy day with falling dewpoints
by the afternoon, though falling dewpoints especially to the
south and west may be offset to some extent by warm
front/isentropic lift which lifts northeast later in the day. No
changes to highs at this point, which appear to be on track.
Previous near-term discussion issued at 530 AM follows...
Pressure gradient between the strong storm system off the New
England Coast and High pressure over the Lower MS valley will
result in a continuation of blustery northwest winds today.
Strongest gusts will be across the the mountain ridges with
occasional gusts of 30-40 kts. Lower elevations will also be
entertained by a stiff breeze with wind gusts of 20-30 kts.
Existing airmass is cold and dry with temperatures in the
20s/30s this morning and dewpoints in the lower teens and single
digits. Cold air advection will continue through at least the
first half of the day, so temperatures will be slow to respond
with afternoon highs struggling to reach 40 in the mountains and
50 in the piedmont. Models are also forecasting SCT-BKN
mid level cloudiness per increasing warm air advection and
isentropic lift aloft. Some low level strato cu will also
straddle the western slopes of the VA/WV highlands with
scattered flurries. Combination of intermittent cloudiness, cold
air advection in the boundary layer, will maintain cool apparent
temperatures throughout the day.
By tonight, surface high pressure will pass overhead resulting
in diminishing winds. This should allow temperatures to slip
into the 20s for lows, but this will depend on overall extent of
the mid/upper level clouds. Models are hinting that at least a
good portion of the CWA will have some mid/upper level
cloudiness for a time during the overnight. As such temperatures
may end up slightly warmer than guidance depending on coverage
and thickness of this cloud cover.
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 400 AM EST Thursday...
The northern stream/northeastern U.S. upper trough will lift
out of the area fairly quickly Friday. Mean upper ridging across
central Canada will shift east through the period, keeping cold
air increasingly blocked and locked up well to our north. In
general, the northern stream, which has been the predominate
flow for our region recently, will lift further north as well
and remain generally north of 40-45 deg latitude through the
period. Meanwhile, the southern stream will remain quite active
yet suppressed fairly far south, generally near the southern
U.S. border/Gulf Coast. A series of vigorous closed circulations
will track through the southern stream as Pacific energy dives
southeast toward the southern CA coast under the mean Canadian
ridge, then tracks eastward near 25-30 deg. latitude finally
beginning to lift northeast as it moves into the southeast
states. As these systems move toward our region, they will be
encountering confluent flow and mean upper ridging, in essence
generally arriving in a much weakened state from the form they
will take across the southwest and south central U.S.
The first southern stream system to reach our area will arrive
Saturday night and Sunday. Models in generally good agreement on
the timing of this system, although differ on how much
precipitation it will produce across the region. As noted above,
this system will be in a weakening state moving into a mean
ridge prevailing across the Mid-Atlantic/eastern U.S. It will
also pass through the region fairly quickly as it is being
booted out by a much stronger southern stream system moving into
the far southwest/deep south Texas late in the weekend. The
antecedent air mass across our region as this system arrives
will be dry with dewpoints only in the 30s to lower 40s.
Precipitation will generally fall from mid-level clouds and
produce nominal amounts mostly less than 1/4 inch Saturday night
into Sunday morning. The most likely area for meaningful
precipitation with this system appears to be west of the Blue
Ridge where isentropic lift will be somewhat better. There is no
threat of winter precipitation with temperatures well above
freezing and the air mass is entirely too stable for any thought
of thunder. The short wave will exit the area Sunday evening as
a high amplitude ridge evolves across the region in advance of
the slow moving deep southwest/south central U.S. system
850mb temperatures will warm dramatically during this period as
mean ridging evolves over the area and the source of any
Canadian air lifts well north of the region. Most models are in
agreement that 850mb temperatures will level off in the +12C to
+14C level over the weekend and generally remain in place at
such levels into the new week. Although Friday morning will
start cold as the Canadian air mass rapidly retreats, afternoon
temperatures will reach the upper 50s to lower 60s, some 10-15
degrees above normal despite mid-level warm advection cloud
cover streaming from northwest to southeast across the CWA. This
cloud cover will be associated with the northward lifting
northern stream. On Saturday, mid/high cloud cover will be on
the increase from the south as the weakening southern stream
system approaches the area. This will leave Saturday`s
temperatures only a few degrees above those observed Friday,
yet still a good 15 degrees above normal across the CWA. After
Friday morning, below freezing temperatures are generally not
expected. Sunday will see temperatures on par with Saturday with
clouds and light rain in the morning, becoming partly cloudy
during the afternoon.
.LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 430 AM EST Thursday...
Extended period of unseasonably warm temperatures to continue.
Mean ridging across central Canada will gradually shift eastward
into eastern Canada. This will keep the northern stream and any
source of Canadian/Arctic air mostly north of the U.S. Canadian
border through the period. The result will be well above normal
temperatures throughout the entire period and beyond. The warm
air mass will be locked in place across the eastern U.S. with
the cold air blocked to our north and high amplitude mean
ridging across the eastern U.S. drifting only slowly east
through the period in advance of a strong, closed low
circulation across deep south Texas into the Gulf through the
period. 500mb heights are expected to hover near 580dm through
the period with 850mb temps averaging in the +12C to +14C range.
There remain some significant differences on how the
aforementioned southern stream system will eventually impact our
region. The ECMWF keeps this system on a very far southern track
taking it slowly across the Gulf and into Florida late in the
week. Meanwhile, the GFS paints a much dirtier picture, keeping
the main low track far to the south, but allowing associated
pieces of weak energy to lift north into the TN Valley and Mid-
Atlantic region. The Canadian is very bullish with the southern
stream system lifting it further north into GA and developing a
strong wedge across our area with overrunning precipitation. At
any rate, given this is a closed, vertically stacked,
essentially barotropic system, it will be very slow to move east
and the main effects do indeed appear to remain well to our
south. We should begin to see an increase in clouds as we head
into Wednesday, but timing and amounts of precipitation remain
questionable, but certainly none before Wednesday at the
earliest. ECMWF MOS creeps pops into the slight chance category
by Wed, while the GFS gets into the high chance range. For now,
have confined mentionable pops mainly to west/southwest areas
Wed, with Mon-Tue dry.
As noted above, with 850mb temps stuck in the +10C to +14C range much
of the period, surface temperatures will continue to be well
above normal, with max temps in the 60s west to lower 70s east
with lows only in the 40s. These readings are a good 15-20
degrees above normal. Certainly no signs of any winter weather
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --As of 1240 PM EST Thursday...
VFR through the TAF period. Main effect on aviation interests
this TAF period will be continued gusty northwest winds up to 30
kts at ROA, as well as potential for turbulence due to potential
mountain wave activity in/around the Blue Ridge. These should
primarily last through 00z with a decrease in speeds and gusts
to light/variable conditions overnight. While FEW- SCT fair wx
cu persist across the TAFs, will see an increase in mainly mid-
level cloud cover from SW to NE as a dry warm front advances
northeastward. Gradual thinning/decrease in mid-level cloud
cover anticipated by Friday afternoon.
Extended Aviation Discussion...
VFR conditions remain the rule through Saturday. Next potential
for sub- VFR conditions is late Saturday into Sunday as a
disturbance moves into the area from the Deep South. Warmer
temperatures will accompany this system, so any precipitation
should be in the form of rain showers. Lower ceilings associated
with these showers may linger into Sunday before clearing and
return to VFR Sunday night through Monday. Dry weather will
prevail Monday night into Tuesday.
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