Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
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FXUS61 KRNK 201736
Area Forecast Discussion
National Weather Service Blacksburg VA
136 PM EDT Tue Sep 20 2016
An upper low combined with the remnants of former Tropical Storm
Julia will meander about eastern North Carolina and South Carolina
through late week before finally shifting out into the Atlantic
ocean. This will keep fairly unsettled conditions east of the Blue
Ridge over the next several days, less so in western areas. High
pressure will gradually build in from the west during the later
half of the week before a cold front approaches late in the
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 130 PM EDT Tuesday...
Slowed the arrival of showers into the piedmont. With more sun
and less rain this afternoon, increase temperatures a few degrees
especially across the foothills and mountains.
As of 330 AM EDT Tuesday...
A fairly complicated forecast through this period as a weak upper
low cuts off across the Carolinas. This upper low is combined from
the remnants of former T.S. Julia and an upper trough that cutoff
from the westerlies yesterday. Models continue to offer several
solutions as to how far west and north tropical moisture from
these combined systems will track back into the RNK CWA. The GFS
tends to be fairly dry keeping the associated rainfall closer to
the coast, while the NAM/Canadian/ECMWF spread the moisture much
further back west and north, all the way to the Blue Ridge. ECMWF
QPF is excessive, while the GFS is minimal at best. The concern,
however, is that the ECMWF, NAM, and Canadian are more similar in
QPF amounts, namely several inches as compared to the GFS. Having
said this, all models are in good agreement that more appreciable
rain will not spread back into the CWA until later today or this
evening. The HRRR and NCEP WRF models show little to no
precipitation making it any further west than the eastern parts of
the Piedmont today/this afternoon. Mid-level air spreading east
from the TN/OH valley is quite dry with mean RH less than 15%.
Therefore, in agreement with other offices, have decreased pops
for today/this afternoon, then increased into the high chance
range along RAH border after 00Z when a weak spiral band is
evident moving west into the region.
As always with this type of pattern of high tropical PWAT air
yielding an efficient warm rain process and enhanced upslope
easterly flow developing, there are concerns of enhanced, heavy
rainfall along the east slopes of the Blue Ridge. This will
certainly need to be watched over the next few days.
While we are almost a year to the date of a very heavy
rain/flooding event that evolved along the Blue Ridge in 2015,
the synoptic pattern this week is not similar. Several features in
place during the event last year are lacking at this time. We
lack a T.D. moving north out of the Gulf with PWATS in excess of
2.0 inches, an upper trough to the west, a stationary front over
the region, and strong easterly flow to the east of the front
thanks to a strong surface high over New England. So, at this
point, concerns are far less than at this time last year for such
type of event. Nonetheless, as noted above, we will need to keep a
close eye as the ECMWF/NAM/Canadian depict several inches of
rainfall across eastern NC very close to the RNK border and we are
dealing with remnants of a tropical storm, always problematic. The
key take away here is that confidence is low that the deep
tropical moisture from remnant Julia will ever make it this far
west. It is more likely to stay across the coastal plain in
association with the coastal trough.
As has been the case for weeks, no appreciable change in 850mb
temps noted through the forecast period. Temperatures will largely
be dependent on cloud cover today, less in the west, more in the
east. This will most likely yield max temps in the upper 70s to
lower 80s with lows in the upper 50s to mid 60s. These
temperatures are 5-10 degrees above normal, especially min
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.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
As of 315 AM EDT Tuesday...
During this portion of the forecast, a frontal boundary will remain
stalled from near Jacksonville, FL, northeast along the east coast
to the Outer Banks of North Carolina. A closed upper low will
meander north and south along this boundary, and be centered
somewhere near the coast of South Carolina.
Model guidance varies as to the degree to which moisture on the
northern side of this system gets advected into parts of our region.
The GFS is the driest with little if any precipitation impacting our
area. The ECMWF, NAM, and Canadian solutions all to some degree
offer solutions that have precipitation impacting roughly the
southern third of the region, with the greatest concentration
across the southeast parts of the area. WPC also has been leaning
towards this wetter scenario as noted in their QPF forecasts.
Our ongoing forecast has been been mirroring these wetter solutions,
and the one from this morning will continue likewise. The biggest
alteration will be a slight shift southeast of the northern most
extent of the slight chance probabilities. Other than that, the
general orientation of the precipitation in the forecast has been
altered very little.
By Friday into Friday night, the guidance is in fairly good
agreement that the closed low will transition into an open wave and
start to progress more out to sea. This process will allow for a
decrease in coverage across the southern sections of the area. By
late Friday night, all the precipitation is expected to be out of
Thanks to decreasing wind speeds, less cloud cover, and a moist
boundary layer, late night and early morning river and mountain
valley fog is expected, especially by Thursday night and Friday
.LONG TERM /SATURDAY THROUGH MONDAY/...
As of 330 PM EDT Monday...
The weak closed 500mb low opens to become absorbed in the general
west to east flow which gradually takes the clouds and rain east and
off the Atlantic coast Friday night.
Upper ridge strengthens by Saturday morning but remains undercut by
low level southeast flow Saturday ahead of a shallow backdoor front
that may slide south into the area by Sunday. This supports isolated
diurnal pops Saturday before deeper upstream moisture ahead of a
stronger Midwest cold front works east along the backdoor boundary
resulting in perhaps more widespread showers by early next week.
Leaned temperatures towards Superblend with cooler readings
especially for Sunday and Monday with moderating high
temperatures for Tuesday.
.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --As of 140 PM EDT Tuesday...
Weather through the TAF valid period will be driven largely by
remnants of T.S. Julia and a stalled frontal boundary along the
coast. This will result in a strengthening northeast flow and even
low end gusts across the Piedmont this afternoon. This will also
keep low-end VFR clouds across the piedmont, moreso towards KDAN.
Areas across the foothills and west of the Blue Ridge will
see scattered fair weather cumulus through the rest of today.
Outer bands of light rain may creep toward Danville tonight with the
best chance toward sunrise based on 12z model data. Western valleys
will likely see a repeat of the dense ground fog after 06Z Wed,
although confidence in this occurring is not as high as it was this
Extended aviation discussion...
Wednesday through Friday, outside of late night/early morning
fog/low clouds, expect mainly VFR conditions with the caveat to this
being any lingering slight chance of showers from Julia per
GFS/ECMWF, mainly affecting areas east of the Blue Ridge.
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