Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 261141
Area Forecast Discussion
National Weather Service Blacksburg VA
741 AM EDT Fri Aug 26 2016
High pressure will be the dominant weather feature through the
upcoming weekend...becoming centered directly overhead by Saturday.
A cold front may slowly slide southward into the area by the middle
of next week. A tropical low will gradually strengthen off the
southern tip of Florida early next week and then possibly move
off the coast through the week.
.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM EDT Friday...
Mostly clear skies with light winds has resulted in patchy low
clouds and fog this morning. Strong subtropical ridge of high
pressure will remain across our region today and tonight.
An isolated shower or thunderstorm may be possible this afternoon
mainly over the southern Blue Ridge. It will be hot and humid this
afternoon. Heat indices in the Piedmont should stay just below the
century mark. High temperatures will range from the lower 80s in the
northwest mountains to the mid 90s in the Piedmont. Clear to partly
cloudy conditions expected tonight with areas of fog, especially in
the western mountain valleys. Low temperatures tonight will drop
into the lower 60s in the west to the lower 70s in Piedmont.
.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
As of 400 AM EDT Friday...
A strong 596dm upper ridge will be centered over the region yet
Saturday, with the center actually very near KROA or KBCB. Expect
strong subsidence with warm temperatures aloft, +20C to +22C at
850mb and -4C to -5C at 500mb. The old cold dissipating cold front
will likely lie across central NC into northern GA at this point.
Most models develop a fair amount of convection and associated
QPF around the western and southern periphery of the upper high as
well as near the front, but especially across northwest NC and
northeast TN. This appears overdone given the synoptic pattern in
place, so have stuck with slight chance/20% pops mainly along and
west of the Alleghany front/Blue Ridge, or primarily west of of
I-77. In addition, models hang on to convection too long after 00Z
as with no dynamics, activity will almost entirely be diurnally
driven and dissipate quickly with the loss of daytime heating. Am
not advertising pops in the 06Z to 12Z time frame. Temperatures
will remain very warm Saturday and a good 10 degrees above normal,
both lows and highs, with abnormally high dewpoints as well for
late August. Look for highs still in the low to mid 90s across the
Piedmont, with mostly 80s west. Lows will still only be in the
60s west to lower 70s east with dewpoints still hovering in the
60s to lower 70s same areas.
For Sunday, the upper ridge shows signs of weakening and shifting
just south of the area, but nonetheless remains the underlying
theme of the synoptic pattern across the eastern U.S. A new weak
cold front is evident across the OH valley into western PA/NY.
This will be too far north of the RNK CWA to have any impact on
our sensible weather at this point. There should again be
diurnally driven convection mainly across the mountains and along
the western periphery of the upper high, namely southern WV
southward through eastern TN and western NC. Overall coverage
should be on par with Saturday to perhaps less, with little to no
activity across the Piedmont. Again, convection should weaken
quickly with the loss of daytime heating. With upper heights and
850mb temps dropping a tad, expect daytime max temps to overall
drop 1-2F across the CWA, yet still leaving readings well above
By Monday, the ridge continues to weaken slightly, yet remains the
dominate feature for much of the mid latitudes of the U.S. A new
west-east oriented weak cold front beings to drift toward the
region from the north. As a result, most models indicate a slight
uptick in convection across northern WV/northern VA toward the
I-64 corridor by afternoon. Dynamics remain weak, but slight
cooling aloft may provide for slightly better coverage northern
areas than expected over the weekend. Southern parts of the CWA
should remain mostly rain free. Temperatures will remain above
normal, but instead of 10 degrees above normal, should be more on
the order of 7-8 degrees above normal. Minimum temps will continue
to show the greatest positive departures from normal, in the mid
60s west to lower 70s east.
.LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 430 AM EDT Friday...
As with previous days, the main concern during the extended
periods continues to revolve around a potential southeastern U.S.
tropical system. Models continue to exhibit notable differences,
but the general trend is toward a weak tropical low to drift into
south Florida early to mid part of next week, then move northeast
along the FL/GA/SC coast. The ECMWF has shown the most deviation
from previous forecasts, now advertising a much weaker system than
previous runs, and much closer to what the GFS has been
advertising for the past several runs. This leave the RNK CWA
largely unaffected on the northwest/dry side of the system with
the main concern being the aforementioned front lingering across
the region. It is quite possible that the RNK CWA will have no
impact at all from this tropical system, but the exact solution
remains to be seen.
The trend to a weaker and further east tropical system is largely
driven by a deeper trough now progged to develop across the
northeast U.S. during the mid and later part of next week. This
would tend to shunt the effects of a tropical system further east
and quicker out to sea.
Another feature of note that all models are picking up on is a
weak tropical system now slated to develop along the TX Gulf Coast
early next week. The moisture from this system could track north
and northeast along the weak southward moving frontal boundary and
enhance precipitation. However, for now, this appears to mainly be
a concern for the Midwest, not here. Despite these changes, there
is still not clear consensus to advertise anything greater than
slight chance to low chance pops with weak forcing and limited
synoptic systems of importance through this period.
Maximum temperatures should continue to slowly cool during the
period with a tendency toward upper troughing and lowering upper
heights. Increased cloud cover will also help. Maximum
temperatures will be mostly in the 80s through the period, except
70s mountains. However, PWAT/RH values will remain high and
minimum temperatures will remain well above normal in the 60s
mountains to lower 70s Piedmont.
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
As of 735 AM EDT Friday...
High pressure both surface and aloft will control our weather
today and tonight. Outside of morning fog and very isolated
convection mainly along the western periphery of the CWA, great
flying weather is expected. This morning, the combination of light
winds and abundant low level moisture has produced patches of
dense fog. KLWB and LBCB both seeing LIFR-VLIFR conditions in
localized dense fog and VV cigs. KLYH and KDAN have MVFR
conditions. Fog and associated cigs will burn off within a couple
of hours after sunrise. For the remainder of the day, just sct VFR
CU expected with strong subsidence aloft in place. Any convection
too isolated and likely west of any of the TAF sites. Only site
that may see convection nearby should be KBLF. Models do show a
period of mid clouds traversing the region during the mid to late
afternoon, so have introduced some 080-100kft clouds as a result.
Fog and associated ceilings will likely develop again after 06Z in
the usual spots, namely KLWB, KBCB, and KLWB in the very moist,
stagnant air mass. Winds will be light NW-NNE through the TAF
valid period at 4-7kts, becoming mostly calm after 00Z.
Medium to high confidence in cigs and vsbys through the TAF valid
Medium to high confidence in wind direction through the TAF valid
period, with high confidence in wind speed through the TAF valid
Extended aviation discussion...
Strong ridging to hold tight on Saturday with continued VFR and
again only isolated late day mountain shra/tsra resulting in
possible brief MVFR.
A weak front will drift into the area Sunday. Isolated to
scattered diurnal showers and thunderstorms still possible into
Sunday evening. Coverage will be limited in area and duration.
Monday high pressure bubbles in but still a very humid airmass to
keep isolated mountain storms around in the afternoon, but mainly
VFR. Another front situated north of us Tuesday could enhance
convective threat, mainly over the mountains and north of ROA/LYH.