Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 181351
Area Forecast Discussion
National Weather Service Blacksburg VA
951 AM EDT Thu Aug 18 2016
A weak residual boundary across the region will continue to
dissipate today allowing weak high pressure to slide in from the
west overnight into Friday. A strong cold front over the central
United States on Friday will cross through the region late Sunday
into Sunday night. Somewhat cooler and drier air follows the front
for early next week.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 952 AM EDT Thursday...
Made some minor adjustments in pops shaping towards WSR-88d images
and trends for this morning, then leaned towards HRRR for late
morning into this afternoon. Overall, it still looks like the
best chance of for best convective for this afternoon will be in
southwest portions of CWA especially along and west of I-77. More
As of 230 AM EDT Thursday...
Overall zonal flow aloft to remain in place through the next 24 hours
with subtle lowering of upper heights slowly flattening the offshore
ridge to the south into tonight. However water vapor shows the plume of
deeper moisture now across the area from the southwest with the residual
surface boundary having basically washed out just to the north. This
will make for more uncertainty with pops into this evening given added
shortwave energy sliding into the southwest zones while pwats slowly
decrease from north to south in the wake of the shortwave from late
yesterday. Latest short term guidance also showing weak west/northwest
flow across much of the region today following this feature with the
remnant axis of the boundary/outflow now over southern/southwest sections.
This looks to be the area for best convective chances, espcly along/west
of I-77, as well as into northwest NC, where the flow may turn southwest
ahead of the impulse and forecast instability is a bit more.
Otherwise like most chance pops south of highway 460 today with perhaps
mostly dry far north after any early morning shra fade. Weak but
unidirectional flow aloft suggests some potential for more banded
convection espcly south but parameters less for much more than isolated
pulse severe at this point. High temps not quite as hot out east given
slight cooling aloft and mid clouds that could limit rises over the
west where some spots may stay in the 70s/low 80s. However with weak
downslope appears will still be around 90 Piedmont sections with overall 80s
elsewhere pending exodus of the mid deck.
Latest ensembles suggest that isolated convection could linger south/west
into this evening with continued westerly flow perhaps keeping some
shra threat over the far west overnight. Since guidance showing a
gradual return of moisture southwest late, while having added
shortwave energy shear in from the west, leaving in some low chance
pops I-77 corridor overnight, but mainly dry elsewhere with fog
around. Lows likely a little cooler with dewpoints slightly lower
allowing most to drop back into the 60s outside of the far southeast.
-- End Changed Discussion --
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 300 AM EDT Thursday...
A lee trough will shift east over the coastal piedmont on Friday
with a washed-out boundary in the vicinity of the TN/VA-VA/NC
border. A mid level short wave is expected to track over the
southern Ohio Valley Friday morning, then move over the south-
central Appalachains Friday evening. This wave and lingering
boundaries in the area will bring another chance for showers across
the mountains Friday morning, then a chance for thunderstorms for
the entire area during the afternoon and evening. The strongest of
the storms should reside along and south of the VA/NC border. The
overall threat for widespread severe storms Friday will be low. The
short wave will pass to the east during the evening with the flow
becoming zonal going into Saturday. This zonal flow will limit
showers and thunderstorms across the area Saturday afternoon,
however a few pulse storms could become severe. It is worth noting
that the GFS wants to bring a wave across the Tennessee Valley which
could bring more areal coverage of storms Saturday, but appears to
be the outlier. Most models are holding the more widespread showers
and thunderstorms with a strong cold front on Sunday.
Temperatures will continue to remain above normal each afternoon
through Sunday. Temperatures will range from the low to mid 80s west
and near 90F over the piedmont. Overnight lows will remain muggy and
in the mid 60s to low 70s.
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 235 PM EDT Wednesday...
A strong cold front will approach the region Sunday morning, and
cross the area either Sunday night or early Monday morning. Guidance
is still flip-flopping on this detail. In advance of the front, look
for a significant increase in the coverage of showers and storms. In
the wake of the front, either Monday morning or Monday afternoon,
the area is expected to experience its first notable change in
airmass that has occurred in some time.
A cooler air mass with lower dew points will be in place across the
area by Tuesday and Wednesday. Both of these days, expect highs
across the mountains in the mid 70s to near 80 with the low to mid
80s across the Piedmont. Low temperatures will range from the mid to
upper 50s across the mountains to the low to mid 60s across the
.AVIATION /14Z THURSDAY THROUGH MONDAY/...
As of 700 AM EDT Thursday...
Lower IFR to MVFR cigs persist in spots across the far west early
this morning with mid deck VFR canopy elsewhere where seeing some
lighter showers still ongoing. Expect only slow improvement around
KBLF with weak upslope and added upstream light showers likely
holding sub-VFR in place until early afternoon. May also see lower
MVFR cigs fill in over the next couple of hours at KLWB/KBCB/KROA
before slowly mixing out by late morning into early afternoon
with heating. However mid deck canopy may be slow to exit with
strato- cu also possibly lingering before the next wave over the
TN valley arrives. In addition once heating takes shape expect to
see more cumulus buildups in the afternoon but to a lesser extent
than previous days given less instability and lingering mid
clouds. Convective coverage also iffy with main focus likely over
southern/southwest sections where somewhat drier air aloft wont
work into before the impulse arrives from the west. Think other
than KDAN/KBLF, too uncertain to include any vicinity mention of
shra/tsra with most sites likely to stay dry after early
sprinkles/showers under more clouds south and less across the
north later in the day.
Showers may again linger across the south this evening before
fading to patchy MVFR/IFR fog prior to clouds returning north
Extended aviation discussion...
Deeper moisture to the south will start to return north Friday
with coverage of showers and storms spreading back across the
region by late in the day. This should bring a return of periodic
sub-VFR in shra/tsra into Friday evening, with added at least
scattered coverage again Saturday afternoon given deeper moisture
in place. Best likelihood of more widespread showers and storms
including MVFR/IFR will take place Sunday ahead of a strong cold
front that will arrive Sunday night. Much drier air then looks to
return VFR to the region behind the front on Monday.