Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 241742
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
142 PM EDT Sat Jun 24 2017

.SYNOPSIS...
The remnants of former T.S. Cindy, located over northern
Virginia this morning will accelerate northeast of the Mid-
Atlantic coast by evening as upper troughing deepens across the
Great Lakes. A weak cold front will push slowly southeast
through the day, then southeast of the area by Sunday morning.
Upper troughing will remain in place through much of the
upcoming week, but at the surface weak high pressure will hold
until late week, leaving the area with mostly dry conditions
until late week with slightly below normal temperatures.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1255 PM EDT Saturday...

The biggest adjustments to the forecast for this afternoon is
an increase in forecast high temperatures by roughly two to four
degrees across the eastern parts of the area. A bit more
sunshine was received than earlier anticipated across the region
which allowed the increase. Clouds are now advancing into that
area, so the rate of increase should start to decrease, but
there will still be enough sunshine to warrant the forecast high
increase. Adjusted precipitation forecast from this morning is
on track with isolated showers now located across North Carolina
generally along and west of I-77.

As of 955 AM EDT Saturday...

The biggest forecast adjustment for today is a increase in
arrival time of clouds and isolated to scattered showers over
and east of the Foothills and neighboring sections of southwest
Virginia. Latest radar trends and the most recent meso-scale
models suggest arrival about three to four hours later than
those earlier advertised. Have adjusted the forecast
accordingly. The only other adjustment is a reflection of the
current observations of temperature, dew point, and wind with
expected trends into the early afternoon.

As of 415 AM EDT Saturday...

Surface pressure analysis shows that the remnants of T.S. Cindy
tracked through the heart of the CWA overnight and early this
morning were located over Loudon county VA, just west of D.C.
Any area of showers and gusty winds moved quickly through the
CWA just after midnight blowing a few trees down in the Henry
County VA/Rockingham County NC area, but other than that it was
just a breezy and muggy night, albeit about 10 degrees cooler
with the passage of the showers and Cindy.

So, we are done with problems associated with Cindy now as it is
progged to continue racing off quickly to the east-northeast
amidst strengthening 500mb flow thanks to a trough deepening
over the Great Lakes. A trailing cold front, will be much slower
to push south of the area, as the flow aloft is largely parallel
to the front. With the trough deepening, the front will
eventually sag south of the CWA later tonight and early Sunday.
Convective allowing models in addition to most of the synoptic
scale models, indicate good potential for showers and
thunderstorms to develop across eastern TN/western NC and
perhaps even into far southwest VA, such as the Grayson/Carroll
county area, this afternoon, before drifting east-southeast
through the evening. Brooks-Craven parameters suggest that there
is even some potential for a few severe storms, but mainly
closer to the I-40 corridor just south of the CWA. SPC has
indicated a marginal risk for severe this afternoon/evening, but
has kept it just south of our CWA with general thunder indicated
to the northwest into most of the areas previously mentioned.
With the wind fields much weaker than was the case earlier with
the passage of the remnants of T.S. Cindy, main threat would be
locally heavy downpours, CG lightning, and perhaps small
hail/localized wind gusts.

Any threat of convection will end very quickly after sunset with
the boundary shifting southeast of the area under the deepening
upper trough. Cooler/drier air will start to filter further
southeast overnight and Sunday morning will start off quite a
bit cooler than we have seen in the past few days with lows
ranging from the 50s in the northwest to the 60s in the
southeast with dewpoints dropping into the 50s northwest to the
60s southeast. This will end the daily thunderstorm threat for
the next few days.

The passing remnants of T.S. Cindy and the deepening upper
trough/lower heights will lead to fairly breezy conditions
today, so some wind gusts into the 20-25 mph range not out of
the question at all. But for most of us, especially north and
west of the Blue Ridge, it will be a very pleasant Saturday.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
As of 330 AM EDT Sunday...

A broad upper level trough will reside over the eastern half of the
US through early next week. Northwest winds will usher in cooler
drier air both Sunday and Monday. Besides some fair weather cumulus
clouds forming in the afternoon, both days look very comfortable.
Afternoon temperatures will average 3F-5F cooler than normal. Dew
points will range from the upper 40s across the mountains to upper
50s in the piedmont. No rain is expected until Tuesday afternoon.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
As of 339 PM EDT Friday...

The long range models are in good agreement with the overall upper
air pattern during this period with an anomalously deep upper trof
over the eastern U.S. early in this period, with 500mb heights 2-3
standard deviations below normal,transitioning to a zonal flow by
mid week, with ridging building by the end of the week.

The 12Z GFS is still fastest with the eastward progression of the
upper trof Tuesday night into Wednesday, but this has little impact
on the tranquil weather expected during this time. A weak frontal
boundary moving through early Tuesday morning may generate some
spotty showers in the mountains, but forecast RAOBS indicate there
will be very little moisture available. Otherwise, PWAT values will
remain below average until Thursday night/Friday so expect a
prolonged period of dry weather. By late in the week...a deep
southwest flow developing on the west side of an upper ridge and
ahead of an approaching upper trof in the upper mid west will
increase moisture and provide the opportunity for weak upper level
disturbances to pass over our area. This will result in increase
chances for scattered thunderstorms during this period.

As for temperatures, forecast 850mb temps from the GEFS are 2-3
standard deviations below average, which will lead to some cool
mornings Tuesday and Wednesday. Adjusted low temperatures down a
couple of degrees below guidance during this period. Temperatures
will moderate late in the week.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 130 PM EDT Saturday...

Isolated to scattered showers are expected the remainder of the
afternoon and into the early evening between roughly KTNB-KDAN.
MVFR to low end VFR ceiling are expected within this region with
mainly VFR ceilings north of this area. Visibilities will be
primarily VFR with brief IFR/MVFR visibilities associated with
the heavier showers or stray thunderstorm that develops. The
activity should wane around sunset as we lose the heating of the
day and the cold front partially responsible for the activity
moves southeast.

Overnight, most of the area will experience VFR conditions.
Areas between roughly KLWB-KBLF will encounter a brief period of
MVFR/IFR ceilings late tonight as low level moisture, and weak
upslope flow, combined to yield some stratus. Any sub-VFR
conditions should improve quickly to VFR a little after sunrise
Sunday. Winds will gradually increase Sunday morning from the
northwest with gusts around 15 to 20 mph possible across the
mountains.

Confidence is moderate to high regarding this portion of the
aviation discussion.

Extended Aviation Discussion...

Other than the potential for some brief late night/early
morning mountain and river valley fog, VFR conditions are
expected to prevail through Thursday.

On Friday, the potential will increase for some brief, localized
sub-VFR conditions as showers and thunderstorm chances
increase.

Confidence is high regarding this portion of the aviation
discussion.

&&

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

&&

$$
SYNOPSIS...RAB
NEAR TERM...DS/RAB
SHORT TERM...RCS
LONG TERM...PH/RCS
AVIATION...DS


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