Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 231744
Area Forecast Discussion
National Weather Service Blacksburg VA
144 PM EDT Sun Apr 23 2017
Expect wet weather at least through Monday night, with surface
low slowly moving from northern Georgia this morning, to the
NC/SC coast by Tuesday morning, while upper low slowly traverse
the same general area.
.NEAR TERM /THROUGH TONIGHT/...
As of 1024 AM EDT Sunday...
The cold front is pushing south and cool wedge is in place resulting
in clouds and cooler temperatures. Made some minor changes in
temperatures this morning using the GLAMP, with little change in
temperatures throughout the day with highs generally from 50 to
55 across the area. Rain cooled areas in the southwest
mountains may stay in the low 40s. Low pressure in Georgia will
move southeast into South Carolina tonight. This system will
generate rain across our area today into Monday. Rain will be
heavy at times and a flood watch remains in effect until 8pm
Monday. Current radar shows rain in the southwest moving towards
our area. Rain will become widespread this afternoon into
tonight. more changes later this morning...
Previous morning discussion...
As of 734 AM EDT Sunday...
Not much on radar at the moment but upstream area of rain coming
together over Eastern TN, and look for the southern county
warning area to fill back in with rain as upper divergence
shifts to the region after 10am. No other changes needed to the
Expect a lull in heavier showers this morning as we wait for the
positive tilt trough over the Mid-MS valley shift east and become
more neutral then negatively tilted by tonight, while deepening. For
this morning, pockets of deep moisture convergence situated from
the southern Appalachians northeast to the VA piedmont will continue
the shower threat here with less to little coverage over Southeast
WV to the southern Shenandoah Valley. Some fog at the higher
elevations is likely with low clouds in place.
Better lift/jet dynamics/upper difluence start to move into southern
forecast area after mid morning, then shield of rain stays elongated
from Southeast KY/Eastern TN east to the VA/NC piedmont with models
varying on where the heavier rain falls, but based on high-res runs
and track of sfc/upper low, the flow into the southern Blue Ridge
favors higher totals here, this afternoon/evening then expanding
over the Piedmont tonight. Convection should be limited with stable
airmass under high pressure wedge, but cannot rule out some elevated
convection near the NC piedmont south of Danville/South Boston, but
overall not enough support for thunder. Per models, and not
expecting deeper convection, hourly rainfall rates should be
limited, however, still after the past couple of days of scattered
to numerous showers, and adding on another 1-2 inches, with possibly
up to 3 inches near/east of the Blue Ridge south of Roanoke to the
NC piedmont, the flood threat remains for creeks/streams and rivers.
The flash flood threat will be isolated but cannot rule out some
pockets across the southern Blue Ridge this evening.
So in essence after somewhat of a quiet early morning, look for rain
to pick up late this morning and especially this evening and
overnight, when the flow in the low levels increases out of the
east. Late tonight, some potential for dry slot to work toward the
Mountain Empire before the easterly fetch off the Atlantic pulls
rain back to the west Monday.
Temperatures during this time will be cool with upper 40s to lower
50s for most, with coolest readings along the Blue Ridge south of
Roanoke to Boone.
Rainfall overnight will keep temps from falling much but expect 40s
.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
As of 400 AM EDT Sunday...
Vertically stacked cyclone will continue to slowly pinwheel into
central Georgia Monday into Monday night. There still is a good
transport of moisture in southeast flow Monday with PWAT values on
the order of 1.25" along/east of the Blue Ridge and into the
Piedmont, though the highest values are more focused into eastern
sections of North Carolina and eastern Virginia. In addition, stable
thermodynamic profiles owing to residual wedge should keep rainfall
rates lower/more gradual and also likely mitigate any thunder.
Steadiest rainfall and highest PoPs Monday into Monday evening will
also be more focused in the southeast upslope areas in the Blue
Ridge foothills and eastward into the Piedmont, with relatively
lower (Likely tapering to Chance) with more shadowing into southeast
West Virginia and adjacent sections in southwest Virginia. Will also
start to see increasingly more breezy northeast to north winds
particularly in eastern sections later Monday into Monday night.
This is due to a strengthening pressure gradient between high
pressure over the Northeast states and a sub-1000 mb low over the
Carolinas, with northerly isallobaric component also helping to keep
breezy conditions going even into overnight. Highs are only in the
50s tomorrow and fall to lows in the upper 40s to low 50s.
By Tuesday, upper low begins to undergo deamplification with an
eventual track along the Carolina coastline. As the upper low pivots
northward on Tuesday, we should see a northward commahead rain band
brush our Piedmont and Southside counties during the morning hrs,
with accumulations here tending to be two tenth of an inch or less.
Lighter showers in central and western counties are anticipated.
Forcing for precipitation then becomes more nebulous through
the afternoon with a taper-down in PoPs areawide to dry on
Tuesday night. A little less cloudiness in the afternoon should
help to boost highs back into the mid 60s to near 70 with lows
mid 40s to lower 50s.
We return to sunnier, milder and drier weather looking ahead to
Wednesday. The upper low that plagues our weather loses its
influence and pivots into New England, with mid-level ridging
building out ahead of more unsettled weather that looks to evolve
across the central Plains and upper Mississippi Valley.
Southwesterly warm advection pattern begins and temperatures then
return back into the upper 70s to a few 80s.
.LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 400 AM EDT Sunday...
The long wave trough deepens in the central United States putting
the region in broad southwest flow Thursday through Saturday. Models
were showing varying degrees of strength of the southeast ridge. Low
pressure tracking northeast into the Great Lakes will move a front
into the Ohio and Tennessee Valleys on Thursday. This boundary
stalls on Friday before another low moving out of the southern
Plains pushes a warm front into the Ohio Valley on Saturday. This
pattern keeps the rain potential to the west of the Mid Atlantic
states. Temperatures will be above normal Wednesday and
.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --As of 144 PM EDT Sunday...
Poor flying conditions during the taf period with low clouds,
rain and pockets of fog. Rain will continue to lift north this
afternoon and overspread the area from southwest to northeast
with moderate to heavy rain at times, especially along and
south of KROA/KBCB toward KTNB/KMWK/KUKF and KDAN. No thunder
expected at this time, so mainly expected MVFR to IFR vsbys in
rain, with VFR at times, while cigs fluctuate between high end
MVFR to IFR, with higher ridges more prone to lower cigs/vsbys
thru the period. Periods of LIFR can be expected with heavier
rain bands. Widespread low clouds and rain will continue into
Winds will be out of the east mainly around 10kts all sites,
some gusts to 20kts possible near KROA/KBCB/KLYH.
High confidence in ceilings, visibilities and winds during the
Extended Aviation Discussion...
Poor aviation conditions expected to continue through Monday
night, and at times into Tuesday, thanks to the slow moving
upper low and attendant sfc system. Look for gradual improvement
sometime Tuesday from west to east with better flying wx for by
midweek, though another front may bring scattered
MVFR showers/storms toward late Thursday in the mountains. Drier
weather will return for Friday.
-- End Changed Discussion --
As of 330 AM EDT Sunday...
No changes to the flood watch, with still some model differences
in placement of highest rainfall threat. High-res models and
analogs along with pattern recognition favor the southern Blue
Ridge from Roanoke to Boone, east to the piedmont of VA/NC as
those areas which appear to be in line to receive 2-3" today
through early Tuesday. This amount of rain combined with the 1
to 2+ inches that has already fallen since Friday should lead to
hydro issues on rivers, as well as smaller creeks and streams.
Looking at the analogs this pattern favors April 5th, 1993, and
March 27th, 1993 which produced some minor to moderate flooding
along portions of the Dan and Roanoke River mainly downstream of
Danville and Altavista. Still will have to see how this sets up
as we had been dry prior to this event.
WPC has moderate risk of FFG exceeded over the southern Blue
Ridge. As mentioned in the near term, deep convection seems
limited thereby will have to rely on upslope component to
enhance rainfall rates, so isolate flash flooding is possible,
but more longer term >6hr flooding is more likely.
VA...Flood Watch through Monday evening for VAZ007-009>018-022-023-
NC...Flood Watch through Monday evening for NCZ001>006-018>020.
WV...Flood Watch through Monday evening for WVZ042.