Area Forecast Discussion
Issued by NWS Blacksburg, VA
FXUS61 KRNK 301959
Area Forecast Discussion
National Weather Service Blacksburg VA
359 PM EDT Fri Sep 30 2016
A strong upper level area of low pressure centered over Kentucky
will slowly drift to the north later tonight into Saturday. This
system will combine with a residual stationary front across the
region to produce periods of showers and thunderstorms into late
tonight for central and eastern Virginia. The low will move
northeast, away from the region, resulting in drier weather this
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 330 PM Friday...
Showers and thunderstorms continue to develop along the leading
edge of a large nearly stationary cutoff low in the upper levels
of the atmosphere. These showers/storms are initiating in a very
soupy near 70 dewpoint airmass over southside va and the piedmont
of NC and then quickly moving north with the mean wind...the
activity congealing and gradually weakening as the activity passes
into somewhat cooler more stable air in the Shenandoah Valley.
Concerns this evening will be for torrential downpours and
potential for flooding. Greatest rainfall the last 24 hours has
occurred from Bedford north and west into the Highlands of VA
where 3 to as much as 7 inches has been observed, this area
warranting a higher level of threat with respect to flash
flooding. Areas farther east will be under the gun too, but stream
levels not nearly as susceptible to flooding concerns. Never the
less, potential exists for thunderstorms offering a 1 to 3 inch of
rainfall...the higher amounts occurring where training of storms
or repetitive shower activity occurs.
Greatest rain threat through this evening will be along and east
of the highway 220 corridor with likely to categorical pops. A dry
air intrusion aloft will limit coverage farther west with parts of
the forecast area seeing little or no rain. Areas from the
western New River Valley down into the Mountains of North Carolina
and northwest NC piedmont may actually be clear due to the very
dry air moving in from the southwest.
For the overnight and into the day Saturday, the upper low will
finally begin to lift north allowing drier air aloft to overspread
the entire region from southwest to northeast. This should result
in a continued decrease of shower coverage with time with the
entire forecast area clearing out for Saturday. With diminishing
cloud cover, temperatures should dip closer to the seasonal norm
with temperatures falling into the 40s for North Carolina
mountains and from the New River Valley west. Foothills should dip
into the 50s...and low 60s farther north and east where clouds
linger. For Saturday...temperatures expected to rebound into the
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
As of 330 PM EDT Friday...
The closed low will continue to slowly migrate off to the northeast
through the period as it continues to fill and open up, dragging a well
occluded surface low with it. This will position our region essentially
in the dry slot under a neutral thermal advection regime with slight
warming aloft. This should yield essentially a dry forecast through
the weekend. By Sunday night, high pressure pushing in form the upper
midwest will nudge a cold front to our western doorstep before it
stalls, but the best forcing and instability will be shearing off to
our northwest and any chances for frontal precipitation will remain off
to our west. The upper low will give way to ridging in the eastern US
through the early part of next week, allowing a large area of high
pressure to settle over New England and wedge down the east side of the
Appalachians. Moisture will be lacking and isentropic lift over the
wedge will not yet be appreciable do Monday looks to remain dry as well.
Expect temperatures to be seasonable with highs near 80 east of the
Blue Ridge and in the low/mid 70s west. Lows will range from well into
the 40s in the valleys west of the Ridge to the upper 50s east.
.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 330 PM EDT Friday...
The big variable mid to late week lies with the potential track of TS
Matthew as it is expected to turn north and move up the Atlantic coast.
The latest guidance indicates the tropical system will remain far
enough to our east to keep direct effects of this system out of our
region. However, the wedge will remain in place and the squeeze between
the wedge and the tropical system will create enough overrunning to
generate precipitation by late Tuesday/Tuesday night especially in the
east and continuing through the end of the period.
Temperatures in the wedge will remain cool and generally several
degrees below normal.
.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
As of 200 PM EDT Friday...
Cutoff low over the Ohio Valley will remain the primary weather
influence through the upcoming weekend. Scattered to numerous
showers and thunderstorms will be found from the Blue Ridge east
to the coast, in addition to numerous showers underneath the
cutoff low over the ohio valley. A dry slot coming around the
south side of the low will result in little or no activity from
western virginia southward into Georgia. This dry slot is forecast
to move northeast, bringing an end to the shower/storm threat for
central VA/NC by Saturday.
Until then look for areas of showers/storms with sub-vfr
conditions for ROA/LYH/DAN. VFR conditions will be found farther
south and west, although potential exists for late night
fog/stratus and early saturday. Once the fog lifts Saturday,
anticipate a larger area of VFR with only scattered low level
Extended aviation discussion...
The deep upper level low will finally shift farther to the north
by Saturday Night and away from the region on Sunday. The weather
will trend back into a dry pattern with mainly VFR conditions next
week, aside for river valley fog in the mountains resulting in
brief period of late night early morning LIFR conditions at some
of the mountain valley airports.
VA...Flash Flood Watch until 6 PM EDT this evening for VAZ019-020-