Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1129 PM EST Thursday Mar 5 2015
cold high pressure will build east into the region overnight into
Friday bringing drier weather to end the week. This high will
track south of US by Saturday into Sunday. A front moves across by
Near term /through Friday/...
as of 815 PM EST Thursday...
Cloud shield continues to gradually shift east this evening
allowing much drier and colder air with Arctic high pressure to
the west to advect in. However still seeing a few light bands of
flurries/snow showers just east of the Blue Ridge within leftover
residual deep moisture and across the far northwest with the actual 850 mb
boundary. Passage of this feature will also act to produce a few
added upslope snow showers northwest so included low probability of precipitation there and out
east a while longer before clearing sets in as a bit
stronger/drier northwest trajectory develops aloft. This should also
help temperatures fall espcly where deeper snow cover exists over the northwest
as expect some single digit readings which combined with a light
breeze will make for possible Wind Chill Advisory levels on the
ridges late. Otherwise tweaked lows up a bit across the south and
east outside of the snow cover with range from single digits northwest to
low 20s south. Other main concern with refreezing of slush and
water from the earlier snow/sleet so hoisted a Winter Weather
Advisory for black ice in northwest North Carolina...while including a
Special Weather Statement elsewhere for slick conditions into Friday morning.
Update as of 720 PM EST Thursday...
Quick update to drop all remaining headlines for the moment given
tapering of most precipitation to flurries or light snow showers.
Do expect to issue an advisory for black ice over northwest North
Carolina later this evening as well as an Special Weather Statement elsewhere for the
refreezing of water/slush overnight. May also hoist a Wind Chill
Advisory across a few counties over the northwest pending later observation. Few
other changes for now.
Previous discussion as of 250 PM Thursday...
High-res models and 12z NAM did fairly well in axis of precipitation though
differences occurred with thermal profile in this complex event.
Early this afternoon the back edge of the main band of precipitation was
along the Blue Ridge. As we head to the evening this will head east
out of our area. Additional snow/sleet accumulations will be highest
north of a Bedford to Appomattox/Farmville line...where additional 1-
4" could occur...higher toward Buckingham.
The high-res solutions are showing potential for banding setting up
in the Shenandoah Valley south to Franklin County Virginia...and will
follow this solution...but will be interesting to see where and if
it sets up. May get another 1-2 inches out it.
Will let the winter storm warnings/advisories run their
course...though not expecting much more in the mountains.
For the night...will wait until these headlines get close to
expiring then will more than likely be issuing a Winter Weather Advisory
for black ice in our NC counties per agreement with state officials.
In addition...look for enough wind and very cold air to bring wind
chills to sub zero in the Alleghany Highlands of Bath...west to
Greenbrier County WV. Will likely need a Wind Chill Advisory for
For the overnight expect clearing skies with potential for some
cloud cover lingering into morning over southeast WV.
Surface high will shift from the Ohio Valley into the middle Atlantic late
tonight through Friday. Discrepancies exist Friday in terms of cloud
cover with NE flow. GFS showing low level moisture pooling up across
the eastern 2/3rds of the County Warning Area while the NAM/CMC and European model (ecmwf) were
drier. Will lean toward more sun than clouds Friday. Temperatures warm into
the upper 20s to middle 30s area wide...and with more sunshine...expect
most snow cover to melt.
Short term /Friday night through Sunday night/...
as of 230 PM EST Thursday...
High pressure will build into the region on Friday night and remain
across the area through Sunday. A shortwave trough will cross from
the Great Lakes region into New England Saturday night. For most of
our region...a precipitation-free forecast will be offered during
this portion of the forecast. The exception will be parts of
southeast West Virginia where the southern edge of the shortwave
trough may clip this region of and bring some isolated snow showers.
Temperatures during this portion of the forecast will trend milder.
By Sunday night...a split flow pattern will become well established
across Continental U.S.. the GFS...ECMWF...and Canadian model solutions are
all fairly similar on having a disturbance exit the Tennessee Valley
along the northern periphery of the southern jet and traversing the
southern half or our region. Temperatures will be mild enough to
support light rain during the extent of the precipitation. The
northern edge of the rain may reach Route 460. The bulk of the
activity will be near the Virginia/NC border. At this point...the forecast
will only mention low end chance probability of precipitation as its highest probability.
Long term /Monday through Thursday/...
as of 100 PM EST Thursday...
A split flow pattern continues across Continental U.S.. the two streams are
prognosticated to merge across the western Atlantic...a few hundred miles
off the coast of the Middle-Atlantic States. For our region...this will
allow potentially for interaction from both streams. Guidance the
past few days has not been consistent with how much or how little
our area would be impacted...and likewise with the timing of any
potential weather makers. The latest iterations do show a bit more
consistency with each other regarding timing...but not by track. The
GFS...ECMWF...and Canadian solutions offer a solution of a southern
stream system Monday night through Tuesday night. The European model (ecmwf) trends
the system the farthest north...bringing precipitation to the whole
region Monday night and Tuesday. The GFS keeps the system southeast
of our region...with little if any impact. The Canadian solution has
the system clip the southern third or quarter of the forecast area.
Our forecast will continue to favor that of the European model (ecmwf)...but with
toned down precipitation chances. The low level temperature profile
along with expected surface temperatures do not favor a lot of
wintry weather. For the most part....rain will fall with the
system...but there will be a some pockets of snow across the
northern portions of the area Monday night...with pockets of
freezing rain on early Tuesday in the north as low level profile
warms even more.
Tuesday night into Thursday...the jet orientation does not change a
whole lot...and there are weaker signals within the models that
another...and weaker system may brush the southern half of the area
with patchy light rain during this time period.
After only a slight cooling trend on Tuesday...temperatures through
Thursday will trend milder. By Thursday...high temperatures will
range from the middle to upper 50s across the mountains to the lower
60s across the Piedmont.
Aviation /04z Friday through Tuesday/...
as of 1115 PM EST Thursday...
MVFR ceilings over the west will gradually improve overnight as abundant
dry air moves into the region under high pressure. May still see a
some lingering MVFR visibilities as well under small snow shower bands
around kblf through about 07z/2am before moisture fades. Elsewhere
looking at mainly VFR under scattered low clouds near the Blue
Ridge and high canopy out east for a while longer. Expect
clearing skies across the entire area late tonight...with light
winds and VFR conditions during the day Friday and again Friday
Will see continued overall VFR Saturday into Sunday with high
pressure sinking to the south. May be enough moisture with a
clipper passing to the north to generate some western slope MVFR
ceilings and scattered showers Sat night into Sunday. Low pressure
passing from the Gulf of Mexico to off the Carolinas may bring
sub-VFR conditions later Monday night into Tuesday otherwise VFR
pending the track of this system.
as of 810 PM EST Thursday...
Ongoing flooding persists in spots over the west...mainly in
Mercer County while rises slowly leveling off along the Roanoke
River around Roanoke but still rising on the James downstream from
Lick Run. Expect runoff to keep levels near flood a while longer
on the Roanoke around Salem...and close to flood at Buchanan on
the James. Please see the latest wbcflwrnk and wbcflsrnk products
for updates on ongoing flood warnings.
Virginia...Wind Chill Advisory until 10 am EST Friday for vaz019-020-024.
NC...Winter Weather Advisory until noon EST Friday for ncz001>006-
WV...Wind Chill Advisory until 10 am EST Friday for wvz507-508.