-- Discussion containing changed information from previous version are highlighted. --
801
FXUS61 KRNK 240024
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
824 PM EDT Fri Sep 23 2016

.SYNOPSIS...
Low pressure along the coast of the Carolinas will weaken and head
east tonight. A back door cold front enters the area by Saturday
night. As it moves south of us Sunday the flow turns east which
brings in more clouds and a threat of rain into early next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
-- Changed Discussion --
As of 745 PM EDT Friday...

Temperatures were running quite a bit warmer than forecast, so had
to raise them a few degrees over the next few hours. Otherwise,
forecast on track with no cloud cover and zero pops through much
of the night.

As of 310 PM EDT Friday...

An upper level trough across the southeast coast will move offshore
tonight. Heights will build behind this trough from an upper level
ridge centered over the southern Mississippi Valley. Heights will
begin to lower again as a back door cold front approaches the area.
This front may bring in low clouds and light rain late in the
afternoon to the southern Shenadoah Valley. Even though the
atmosphere remains stable, weak convergence over the foothills and
along the Blue Ridge may also pop a few shallow showers in the
afternoon. For now, the best chance for any rain will be north of
I-64. Since this is a slow moving front, Saturday afternoon
temperatures will once again be warmer than normal with widespread
80s, near 90F toward the NC/VA border.
-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 250 PM EDT Friday...

A upper level ridge will be building over the eastern part of the
country through Sunday,  then it flattens Monday into Monday night.

Surface high pressure over central Canada will build southward and
wedge down the east side of the Appalachians. A back door cold front
drops south across the area Saturday night into Sunday. Initial,
shaped the pops for the light upslope with the HiResW-ARW-east and
NAM for Saturday evening into Saturday night. Low temperatures
Saturday night will range from the mid 50s in the mountains to the
mid 60s in the Piedmont.

Look for much cooler conditions behind the front Sunday with a good
deal of low level moisture and isentropic lift over the wedge. The
wedge looks to be solid and wet bulb temperatures are in the 60s so
any precipitation into the wedge will be effective in holding
temperatures down. Lowered high temperatures Sunday to the upper 60s
in the north with wedge to near 80 degrees in far west.

Sunday night will feature plenty of clouds and potential for some
light upslope rain showers.  Low temperatures Sunday night into
Monday morning will generally be from the mid 50s in the northern
mountains to the lower 60s in the southeast.

By Monday evening, the axis of the upper ridge will move to our east
and allow a large closed low over the Great Lakes region to push a
cold front toward the region from the west. Southwest flow ahead of
the front will continue to generate lift over the wedge, while the
western and southern portions of the region on the fringes of the
wedge may get into enough unstable air to support a slight chance of
thunderstorms. Highs on Monday will range from the around 70 in the
northeast to the upper 70s in the western mountains.

Monday night will cloudy with chance of showers. Elected to increase
pops to allow for the mention of likely in northwest Greenbrier
county in Southeast West Virginia. Low temperatures Monday night
will vary from the lower 50s in the northwest mountains to the
mid 60s in the Piedmont.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 230 PM EDT Friday...

A deep upper level low over the Great Lakes will slowly push a cold
front into the region Tuesday. The front and a secondary trof axis
should continue to move east Tuesday night into Wednesday and push
further off the coast Wednesday night into Thursday. (The 12Z GFS is
on the slow end of the guidance envelope, while the 00Z ECMWF shows
a more progressive solution with the surface cold front passage.)
Decided to used Superblend with ensemble solution approach for the
timing with the front. High pressure will build east across the
region Thursday and Friday, then slide into the Atlantic ocean on
Saturday.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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As of 745 PM EDT Friday...

VFR conditions expected throughout most of the TAF valid period,
with the exception of late night/early morning fog in the usual
locations.

Synoptic pattern features a west-east weak cold front sagging
southward through NY/PA this evening. This front will reach the
I-64 corridor by Saturday afternoon, then move toward the NC/VA
border by Saturday evening. It appears the atmosphere will be too
stable and dry in the lower levels for any precipitation with the
front, which is unusual in the east. However, as currently noted,
an extensive area of mid clouds will accompany the front. It
appears that these will mostly be in the 050-080 range, depending
on elevation. So have introduced bkn clouds in this range
beginning Saturday afternoon, but no precipitation.

Confidence is lower than normal in fog development tonight because
of abnormally warm temperatures this afternoon and a dry boundary
layer. Model cross sections and BUFKIT soundings are not favoring
fog development tonight. For this reason, have backed off
advertising LIFR FG at LWB/BCB from a FM group to a TEMPO.

Winds will be light and variable or calm overnight, then becoming
NW 6-8kts after 14Z Saturday.

Medium to high confidence in cigs through the TAF valid period.
Medium confidence in vsbys through 14Z, then high confidence
through the remainder of the TAF valid period. Medium to high
confidence in wind speed/direction through the TAF valid period.

Extended aviation discussion...

As the weekend progresses and the backdoor front stalls just to
our south allowing easterly flow to become established across the
region, low-level moisture increases and a wedge evolves. Expect
cigs to lower into the MVFR category or worse and likely remain in
place through Monday with areas of fog and drizzle or light rain
developing with time as well, especially along the east facing
slopes of the Blue Ridge.

A strong, but slow moving, cold front will be approaching the
area from the west on Tuesday. Models have significant differences
on the timing and location of this front, but rain chances during
the first half of next week will be on the increase.
-- End Changed Discussion --

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...RCS
NEAR TERM...RAB/RCS
SHORT TERM...KK
LONG TERM...KK
AVIATION...RAB/RCS