Special Weather Statement, NWS Blacksburg, VA

Area Forecast Discussion
National Weather Service Blacksburg VA
518 AM EDT Fri Mar 31 2017

.SYNOPSIS...
An upper level low and associated surface trough will pass
across the Mid Atlantic Region today. High pressure will
build across the region for the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 500 AM EDT Friday...

Active weather pattern today with strong upper level low over
the OH Valley with sharp N-S oriented surface trough advancing
east across the lower OH and TN valleys. Large area of showers
and thunderstorms was moving east in advance of this system
with entire forecast area subject to rain today, with widespread
coverage this morning, and scattered coverage this afternoon.
Thunderstorms were embedded within the rain area this morning,
resulting in occasional cloud to ground strikes and brief but
heavy downpours of rain. Rainfall was being enhanced near the
Blue Ridge where upslope southeast wind flow was causing higher
rain rates, rain gages indicating anywhere from 1.5 to 2.5
inches of rain overnight between Laurel Springs and Blowing Rock
NC. These higher rain amounts may result in some localized
flooding, but due to the dry antecedent conditions, the rain
will have less of an impact with respect to flooding and more of
a beneficial effect.

As the surface low over Ohio crosses the mountains this
afternoon, the expectation is for some clearing and a period of
heating east of the Blue Ridge which will result in
destabilization and re-development of a line of thunderstorms
along the actual surface front this afternoon. Main concern
would be areas from Highway 29 and points east where forecast
CAPE of 500-1200 J/KG will promote the development of strong
thunderstorms. With favorable shear anticipated, veering with
height from south to southwesterly and increasing to 40-50 kts
at mid-levels, some of these storms will likely become severe
with potential for rotation, supporting risk for hail, damaging
winds, and isolated tornadoes. The Storm Prediction Center has
outlooked areas east of a LYH-DAN line for Slight Risk of severe
weather for this afternoon.

After the cold frontal passage, conditions will improve with
clearing taking place tonight. As High pressure builds in for
tonight, expect breezy conditions with northwest winds of 15 to
25 mph. West of the Blue Ridge, and more so for the higher
terrain of WV and far western VA and into the NC mountains,
some lingering low clouds and light precip may continue per
shallow moist northwest flow.

Temperatures today will spike just ahead of the cold front with
readings topping out in the 60s, possibly 70 Southside VA and
the Piedmont of NC. Cool air advection tonight will permit low
in the 40s, but well above freezing.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 400 AM EDT Friday...

Northwesterly flow aloft returns along with cold pool of air in low
to mid levels on Saturday. Under slight cold advection aloft, 850 mb
temperatures by early afternoon cool to values ranging from +1 to
+5C. Increasing subsidence along with dry advection should help to
dry up any lingering upslope showers along the western slopes of the
Alleghany Mtns. Mostly sunny skies thereafter lead to a rather
breezy day. While northwesterly flow and adiabatic downslope warming
off the Blue Ridge pushes highs in northern NC and the VA piedmont
into the upper 60s to low 70s, it will only top out in the upper 50s
from the Blue Ridge west and will certainly feel on the brisk side
in these western areas. Ridging builds in Saturday evening with
northwesterly winds diminishing early. Radiational cooling along
with lingering cold pocket of air aloft should lead to near to below
normal lows in the mid 30s to low 40s.

Relatively uneventful Sunday as high pressure is in control. March
sun should push highs back into the 60s to low 70s. However, as the
ridge axis shifts eastward by mid afternoon pattern transitions
toward one of cold air damming. Related sensible weather effects,
that being easterly/southeast surface winds and increased cloud
cover along the Blue Ridge and eastward develops Sunday evening.
Some question how pronounced the CAD becomes as model wind fields at
the surface begin to shift to a southerly direction overnight, in
response to a pronounced parent upper low that digs into the mid-
Mississippi Valley. Actually, the setup as suggested by model
guidance looks pretty similar to that which unfolded in the past 24
hours. Kept lows mainly in the 40s to low 50s.

Active weather then returns for Monday. Early Monday morning, 850 mb
south-southeast winds increase to speeds of 50 to 60 kts which could
lead to breezy conditions along our southern Blue Ridge and NC
mountains. Strongly sheared profile is offered by the GFS with
magnitudes up to 60 kts, though overcast skies and cool near-surface
temperature profiles at this point appear to keep instability values
modest at best. This is not too dissimilar to what's currently
playing out this evening. Certainly need to monitor for potential
thunderstorms particularly in the warm conveyor belt from the Blue
Ridge eastward. Shown slight chances for thunder in this general
area by Monday afternoon. Could see significant variation in spatial
coverage in precip during the afternoon in western and southwestern
counties in the lee of the Blue Ridge given the strong
southerly/southeasterly flow. I've tried to account for this by
keeping PoPs only in the Chance range for the afternoon across parts
of the New River Valley and into the Mountain Empire region, while
trending Likely elsewhere. However, as broader synoptic scale
forcing approaches by evening most everywhere has at least Likely
PoP by that point. QPF forecast also is rather cloudy based on large
QPF bullseyes which may limit northward extent of heavier precip,
though southerly upslope against the Blue Ridge. So, potential for
several concerns including breezy conditions along the southern
ridges as well as thunderstorms/heavy rain. Kept highs in the 60s
with lows mainly in the 50s.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 330 AM EDT Friday...

Model difference expand with the second system late in the long term
period (Wednesday night/Thursday)with 12Z GFS continuing a faster
trend with the approach of a high amplitude upper trof. The 00Z
ECMWF is much slower with the 12Z Canadian starting to trend toward
the faster GFS solution. With individual GEFS ensemble member
showing a large range of solutions, confidence is low on the timing
with this system and leaned toward the Canadian timing which keeps
temps slightly cooler Wednesday and keeps Wednesday dry.

Much colder temperatures are expected behind the system very late
and just beyond (Friday) this period.

&&

.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
As of 200 AM EDT Friday...

Large area of rain with embedded thunderstorms will move across
the Appalachians this morning in advance of a strong upper
level trough of low pressure that will be moving from the OH
Valley across the Mid-Atlantic Region today.

Ceilings are expected to lower to IFR with occasional IFR VSBYs
due to rain and thunderstorms. Conditions will remain poor for
most of the day with improvement late in the day as winds become
westerly in the wake of the storm system.

Extended Aviation Discussion...

High pressure will bring improving conditions during Saturday
although appears sub-VFR cigs along with a few residual showers
may linger at KBLF/KLWB into Saturday afternoon. Otherwise will
see VFR return later Saturday through Sunday under diminishing
winds as high pressure slides across. Next similar low pressure
system to that seen at the end of this week will approach by
Monday with sub-VFR conditions likely returning Sunday night
into Monday as rain again transitions to showers and storms to
start the week.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

SYNOPSIS...PM
NEAR TERM...PM
SHORT TERM...AL
LONG TERM...AL/PH
AVIATION...PM

Hazardous Weather Outlook
National Weather Service Blacksburg VA
631 AM EDT Fri Mar 31 2017

VAZ007-009>014-018>020-WVZ042>044-507-508-011045-
Tazewell-Smyth-Bland-Giles-Wythe-Pulaski-Montgomery-Craig-
Alleghany VA-Bath-Mercer-Summers-Monroe-Eastern Greenbrier-
Western Greenbrier-
631 AM EDT Fri Mar 31 2017

This Hazardous Weather Outlook is for southwest Virginia, west
central Virginia and southeast West Virginia.

.DAY ONE...Today and tonight.

Strong storms today may produce heavy rain and small hail today.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Potential for heavy rain Monday night into Tuesday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

NCZ005-006-VAZ022>024-033>035-043>047-058-059-011045-
Rockingham-Caswell-Roanoke-Botetourt-Rockbridge-Franklin-Bedford-
Amherst-Henry-Pittsylvania-Campbell-Appomattox-Buckingham-Halifax-
Charlotte-
631 AM EDT Fri Mar 31 2017

This Hazardous Weather Outlook is for north central North Carolina,
central Virginia, south central Virginia and west central Virginia.

.DAY ONE...Today and tonight.

There is a risk for severe thunderstorms this afternoon containing
damaging winds and large hail. There is an isolated threat for
tornadoes east of Highway 29.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Potential for heavy rain Monday night into Tuesday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon.

NCZ001>004-018>020-VAZ015>017-032-011045-
Ashe-Alleghany NC-Surry-Stokes-Watauga-Wilkes-Yadkin-Grayson-Carroll-
Floyd-Patrick-
631 AM EDT Fri Mar 31 2017

This Hazardous Weather Outlook is for north central North Carolina,
northwest North Carolina and southwest Virginia.

.DAY ONE...Today and tonight.

Thunderstorms with heavy rain likely today resulting in localized
flooding. There is an isolated risk for severe thunderstorms this
afternoon, storms potentially containing large hail and damaging
wind gusts.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Potential for heavy rain Monday night into Tuesday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

Special Weather Statement
National Weather Service BLACKSBURG VA
413 AM EDT FRI MAR 31 2017

NCZ002-003-019-VAZ012>017-032-310900-
Surry-Wilkes-Alleghany-Grayson-Pulaski-Patrick-Floyd-Montgomery-
Wythe-Carroll-
413 AM EDT FRI MAR 31 2017

...A LINE OF THUNDERSTORMS WILL AFFECT EASTERN
ALLEGHANY...NORTHWESTERN SURRY AND NORTHEASTERN WILKES COUNTIES IN
NORTHWESTERN NORTH CAROLINA...SOUTHEASTERN PULASKI... SOUTHWESTERN
FLOYD...SOUTHEASTERN WYTHE...CARROLL...EASTERN
GRAYSON...SOUTHWESTERN PATRICK AND SOUTHWESTERN MONTGOMERY COUNTIES
IN SOUTHWESTERN VIRGINIA...THE CITY OF RADFORD AND THE CITY OF
GALAX...

At 412 AM EDT, radar indicated thunderstorms located along a line
extending from near Spring Valley to near Stone Mountain State Park
to North Wilkesboro. Movement was northeast at 50 mph.

Winds up to 40 mph and pea size hail are possible with these storms,
along with brief heavy downpours.

Locations impacted include...
Radford...
Mount Airy...
Galax...
North Wilkesboro...
and Hillsville.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

LAT...LON 3715 8055 3691 8046 3660 8054 3611 8113
      3644 8105 3678 8109
TIME...MOT...LOC 0812Z 221DEG 43KT 3670 8110 3643 8107 3618 8113

Loconto

Special Weather Statement
National Weather Service BLACKSBURG VA
652 AM EDT FRI MAR 31 2017

NCZ002>004-019-020-VAZ015>017-032-311145-
Stokes-Surry-Yadkin-Wilkes-Alleghany-Grayson-Patrick-Floyd-Carroll-
652 AM EDT FRI MAR 31 2017

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT
EASTERN ALLEGHANY...SURRY AND EASTERN WILKES COUNTIES IN NORTHWESTERN
NORTH CAROLINA...WESTERN STOKES COUNTY IN NORTH CENTRAL NORTH
CAROLINA...YADKIN COUNTY IN NORTHWESTERN NORTH CAROLINA...FLOYD...
CARROLL...SOUTHEASTERN GRAYSON AND PATRICK COUNTIES IN SOUTHWESTERN
VIRGINIA AND THE CITY OF GALAX...

At 650 AM EDT, radar indicated strong thunderstorms were located
along a line extending from near Glade Valley to near Roaring Gap to
Clingman to near Newton. Movement was northeast at 55 mph.

Winds in excess of 40 mph and pea size hail are possible with these
storms. Brief heavy downpours can be expected as well.

Locations impacted include...
Mount Airy...
Galax...
Elkin...
Fairview...
and Flat Rock.

LAT...LON 3616 8099 3633 8097 3656 8114 3707 8022
      3695 8017 3687 8023 3685 8012 3663 8012
      3626 8027 3626 8045 3614 8044 3611 8051
      3605 8050 3606 8098 3603 8106
TIME...MOT...LOC 1050Z 234DEG 49KT 3653 8106 3636 8093 3619 8096 3565
8125

Loconto