Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 180028

Area Forecast Discussion
National Weather Service Blacksburg VA
828 PM EDT Mon Oct 17 2016

High pressure will take up residency along the southeast coast of
the United States through at least Thursday and provide mild and
dry conditions to our region. A cold front will cross the area
Thursday night into Friday along with its associated showers.
Gusty winds are expected behind the front Friday into Saturday.


As of 820 PM EDT Monday...

Made some minor adjustments to T/Td grids to bring better in line
with current observations. No major changes needed at this point.
Adjusted sky grids to reflect expectation of dense fog along/near
rivers after 06Z and patchy fog elsewhere, clearing around 14Z. No
other changes needed at this time.

As of 215 PM EDT Monday...

The center of surface high pressure was off the coast of NC/SC with
its associated ridge axis extending westward into AL/GA.  An upper
low was located over central Manitoba with is associated occluded
front extending southeast into southern Ontario. The associated warm
front was positioned eastward to near the NY/PA border. Finally, the
associated cold front extended southwest from the triple point into

The location of these features is allowing for a generous southerly
low level flow to advect from the western Gulf of Mexico into the
Mississippi and Lower Ohio River valleys. This fetch is transporting
moist and warmer than normal conditions into this region of the
country for this time of year. A broad upper ridge over the
southeast U.S. is capping what would normally be ripe conditions for
decent coverage of convection in this area. As we progress into the
middle of the week, this relatively mild and moist air will work its
way into our area. While we too will be under the influence of the
capping upper ridge, look for temperatures to trend higher, as well
as dew point readings, but precipitation is not expected.

The warm air advection will have the impact of yielding warmer
ridges overnight as compared to their neighboring valleys by at
least five degrees. Also, most ridgetops will experience
temperatures equal to or slightly greater than the typically warmer
Piedmont region of VA and NC. Wind gusts of 15 to 20 mph can be
expected overnight at the highest elevations. Mountain valleys and
most of the Piedmont region will experience calm or light southwest
winds. This will lead to another night of patchy fog within these

High temperatures on Tuesday are expected to be greater than those
realized today. Readings of the mid 70s to near 80 are forecast for
the mountains with low to mid 80s across the Piedmont. Bluefield,
Blacksburg, and Danville are forecast to reach highs within one
degree of their records for the date. See the CLIMATE section of
this discussion for additional details.


As of 245 PM EDT Monday...

The 12Z GFS and 12Z NAM models continue to advertise a high
amplitude trof deepening from the northern plains to the Mississippi
Valley by Thursday evening. The GFS ensemble mean agrees with this
general idea, but is slightly less amplified.

For our area this means well above temperatures, and some cases,
record warmth for our area on Wednesday. Temperatures will continue
to be well above normal Thursday, but with low level winds backing
in advance of the approaching trof and an increase in high clouds
temps may be a couple of degrees cooler.

Overall, increased temps through the period and continued the trend
of delaying precipitation in the west on Thursday as forecast
soundings continue to indicate an abundance of dry air between 700-
400 mb. With PW values increasing in southeast WV late Thursday
along with weak shortwaves advecting in advance of the approaching
trof in the deep southwest flow, placed highest POPS (still in the
slight chance to low chance category) in this region.


As of 230 PM EDT Monday...

Differences on the timing of the passage of a strong cold front
early in the long term period are still evident in the medium range
models, with the GFS still deeper and slower with the associated
high amplitude upper trof. The 12z ECMWF is trending deeper, but
still not as slow or strong as the GFS, while the 12Z Canadian model
solution also is more progressive with this system.

Leaned toward the more progressive solutions and kept highest POPS
for Thursday night with rain ending in the east early Friday.
Northwest winds will generate some upslope showers into the first
half of the weekend.

Breezy and much cooler conditions will be found for the weekend, and
as the upper flow becomes more zonal early next week, temperatures
will moderate.


As of 745 PM EDT Monday...

High pressure, both at the surface and aloft, will remain over the
region for a couple more days. The surface high is located to the
southeast in a Bermuda High position, providing the region with a
warm southwest flow. With a strong subtropical upper ridge evident
over the area, model cross sections show little to no moisture or
clouds at any levels of the atmosphere, outside the immediate
surface layer near the ground. This has equated to SKC at all TAF
sites with no upstream cirrus slated to spread across the CWA
during this TAF valid period. Thus, the only concern to other VFR
cigs/vsbys through the TAF valid period is late night/early
morning fog as a result of the stagnant air mass and decoupling at
the usual spots.

KLYH, KBCB, and KLWB all saw several hours of LIFR conditions in
fog this morning (Monday) and KDAN saw several hours of MVFR
conditions in BR. While this afternoon was on average 5 degrees
warmer than what was observed Sunday afternoon, temperatures are
already cooling down into the 60s and dewpoints are in the lower
60s. Thus, expect another night of fog and attendant low
clouds/cigs at many locations, with the exception of KBLF and KROA
which will have west flow just off the surface and where fog
development is not expected. Expect the fog and low cigs/vsbys at
KLWB, KBCB, and KLYH roughly in the 06Z to 13Z time frame, with
KDAN likely seeing at least MVFR conditions in the 08Z-12Z time
frame. All of these sites should become VFR no later than 14Z Tue.

Through much of the night, winds will be light SSW-SW at the
surface at speeds 3-5kts. Conditions will decouple, as noted
above, at KLWB, KBCB, and KLYH and winds should become calm at
these locations. While the 850mb winds do increase from the west
late tonight/Tue morning, indications are that winds will not
reach or exceed 30kts within the 2000 ft. layer. Conditions for
LLWS shear appear to marginal to include at this point. KBLF will
have stronger surface winds, so there is definitely no need to
include LWWS there.

Extended aviation discussion...

Through Thursday morning, VFR conditions are expected during the
daylight hours, with redevelopment overnight of river and
mountain valley fog and associated IFR to LIFR stratus
layers/ceilings. Fog will be more widespread each night as the
week progresses due to rising surface dew points and increasing
low level moisture, however increasing winds and mid/high cloud
cover may decrease fog development somewhat Thu morning compared
to Wed morning.

A cold front is expected to move through the region Thursday night
into early Friday. Expect the initial onset of scattered showers
across western sections by Thursday afternoon. A southwest to
northwest wind shift is expected to occur Thursday night across
the region with gusty winds behind the front continuing into
Friday night and possibly Saturday. Areas of sub-VFR conditions
will likely accompany the front and precipitation associated with

A return to VFR conditions is expected for most areas Friday
night into Saturday. The exception may be western parts of the
region where a healthy northwest upslope flow, and lingering low
level moisture, may prolong an IFR/MVFR ceiling during this time


As of 125 AM EDT Monday...

Temperatures will be above seasonal levels for most of the week,
though our record highs may be hard to reach, except for perhaps
for Blacksburg or Bluefield, mainly Wednesday.

Record maximum temperatures through Thursday, Oct 20.

Oct 17

Location      Record Max
Bluefield.....78 in 2000
Danville......88 in 1989
Lynchburg.....88 in 1908
Roanoke.......86 in 1938
Blacksburg....80 in 1989

Oct 18

Location      Record Max
Bluefield.....79 in 2007
Danville......86 in 2007
Lynchburg.....91 in 1938
Roanoke.......91 in 1938
Blacksburg....80 in 1953

Oct 19

Location      Record Max
Bluefield.....81 in 1984
Danville......85 in 1953
Lynchburg.....88 in 1938
Roanoke.......91 in 1938
Blacksburg....80 in 1991

Oct 20

Location      Record Max
Bluefield.....79 in 1993
Danville......88 in 1984
Lynchburg.....85 in 1993
Roanoke.......84 in 2005
Blacksburg....82 in 1985




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