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County Warning Area [CWA]: RNK
Regional NWS Weather Office: Blacksburg, VA
FXUS61 KRNK 240840
Area Forecast Discussion
National Weather Service Blacksburg VA
440 AM EDT Mon Apr 24 2017
Wet weather will persist into Tuesday, as a slow moving area of
Low Pressure moves from the southern Appalachians to along the
South Carolina coast by Tuesday morning.
.NEAR TERM /THROUGH TONIGHT/...
As of 400 AM EDT Monday...
No change to Near Term Forecast. Rain...Heavy at times pretty
much sums it up.
Upper low over the southern Appalachians has ground to a halt,
showing only little movement the last 12 hours and is forecast
to move very little today per being cut-off from the mean upper
level flow. Overall projection is for this feature to drift ever
so slowly to the South Carolina coast by daybreak Tuesday. This
will maintain a deep southeast to easterly fetch of moisture
into our forecast area resulting in a persistent rain with
periods of heavy rain. As such will maintain the Flood Watch for
most of our forecast area along and east of the VA/WV border
and into NC.
As the rainfall continues to add up, expect streams to respond
with small stream flood warnings morphing into larger scale
river flood warnings. River Forecast Centers will be doing a lot
of number crunching this morning, so watch for revised river
forecasts and warning headlines.
Rainfall today is expected to be the heaviest along and east of
the Blue Ridge where the southeast upslope wind component will
add orographic lift. Additional rainfall of 1 to 2 inches is
likely (in some cases on top of the 2 to 4 inches that has
already occured). Heaviest rain thus far has been along and just
west of I-77 from Tazewell and Marion VA, south into Sparta and
Wilkesboro NC. Focus today is expected to shift farther
northeast into the headwaters of the Dan and Roanoke River
Temperatures today and tonight will change very little, cool
northeast to easterly low level wind persisting until the low
drifts off the coast Tuesday.
.SHORT TERM /TUESDAY THROUGH THURSDAY/...
As of 400 AM EDT Monday...
We`ll have one more day of cloudy and rainy/showery conditions on
Tuesday. However, trend will be toward above-normal, more springlike
temperatures looking ahead into the midweek period.
Slow-moving, vertically-stacked cyclone should be roughly centered
over the coastal NC/SC border based on general consensus reflected
in 21z SREF mean/00z global model progs. Little significant change
noted in the projected evolution of the cyclone, that being
deamplificaton and gradual northeastward progress. Moisture plume on
the eastern periphery of the cyclone, associated with PWAT values of
up to 1.3" will continue to be drawn back westward, supporting a
continued period of rain particularly for the central Virginia
Piedmont and into the Southside of Virginia. Weak/nebulous forcing
elsewhere across the CWA supports periods of light showers mainly
during the first half of the day. As upper level low approaches the
Chesapeake Bay and deeper moisture plume is shunted
eastward/northeastward later in the day, PoPs then begin a taper to
slight chance/lower Chance range areawide. An additional tenth to
two-tenths of an inch of rain are possible in central Virginia
associated with the most persistent rain band tapering to a few
hundreths from the Blue Ridge foothills west. Thus a continued wet
outlook but the steadiest and heaviest rains will have since ended.
Aside from southeast West Virginia into western Smyth and Tazewell
Counties in Virginia where at least some partial clearing is
anticipated toward afternoon, for many it will continue to be
another relatively dreary day with highs only in the 60s. Greater
clearing anticipated on Tuesday evening with some radiational
cooling under clearing skies in the upper 40s to mid 50s.
Trend toward warmer temperatures remains on track starting Wednesday
with building 500 mb heights and mostly sunny skies. Our 850 mb
temperatures steadily rise Wednesday into Wednesday night to values
around +14 to +16C. Much milder temperatures well into the 70s to
low 80s anticipated for Wednesday, with lows Wednesday evening into
the low 50s to around 60. These are some 10 to 15 degrees milder
than 1980-2010 climatological normals.
For Thursday, focus shifts to large-scale troughing evolving across
the central Plains states and the ejection of a deamplifying mid-
level trough embedded in deep south-southwest flow, its associated
surface cold front expected to move from the Ohio Valley to the
foothills of the western Appalachians Thursday. I`m hesitant to
introduce slight to low Chance PoPs any earlier than Thursday
afternoon given the amplified southerly mid-level flow that may act
to slow the cold front down than currently depicted in most model
guidance, and we also are capped to any convection out ahead of
this. Generally expect mostly sunny skies through much of the day,
albeit with increasing cloudiness later in the day toward Thursday
evening. Even warmer conditions anticipated on Thursday; aside from
the higher elevations, many areas stand a good shot at reaching the
low to mid 80s particularly east where clouds will be slower to
advance. These are a couple degrees cooler than MEX MOS guidance
which would argue for some upper 80s values in the Piedmont and
.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
As of 300 PM EDT Sunday...
500MB heights rise Friday over the southeast United States but with
an overall deepening upper trough over the central United States. A
deep closed low develops over the Rockies by the end of the week
which will keep much of the east downstream in broad southwest flow.
At the surface a low pressure system tracks into the Great Lakes.
The front with this system stalls in the Ohio and Tennessee Valleys
brushing our far western counties Thursday night and early Friday.
Thereafter, differences become apparent between the 00z GFS and
ECMWF on how far north and east a warm front associated with the
next developing Plains system extends. Generally maintained
continuity with prior forecast for the upcoming weekend until these
details can be better agreed upon. In any event, temperatures
appear to remain above normal.
.AVIATION /08Z MONDAY THROUGH FRIDAY/...
As of 200 AM EDT Monday...
Little change during the 24 hour valid taf period with
widespread rain resulting in IFR cigs and MVFR to ocnl IFR
Slow moving upper low over the southern Appalachian will slowly
drift toward the Mid-Atlantic Coast. This will result in poor
weather conditions across the Carolinas and into Virginia
Extended Aviation Discussion...
Look for gradual improvement 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.
As of 300 PM 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" 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 kept the 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.
Saturated ground may also result in downed trees and rock or
VA...Flood Watch through this evening for VAZ007-009>018-022>024-
NC...Flood Watch through this evening for NCZ001>006-018>020.
WV...Flood Watch through this evening for WVZ042.