Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 270551
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
151 AM EDT Tue Jun 27 2017

.SYNOPSIS...
Weak high pressure over the region tonight will give way to a
fast moving upper level disturbance that should cross the area
from the northwest on Tuesday. Other than some isolated to
scattered showers and storms in association with this feature on
Tuesday, high pressure will provide for dry and cool weather
for much of this week. The chance for more abundant showers and
storms, as well as increasing temperatures, return Friday into
the weekend.

&&

.NEAR TERM /THROUGH TODAY/...
As of 147 AM EDT Tuesday...No significant changes needed with
this update. Did opt to increase sky cover slightly per 3.9
micron infrared imagery showing stream of mid-level cloudiness
ahead of mid-level disturbance over the Great Lakes region, with
leftover altocu layer generally near/north of the Roanoke
Valley. Other than that minor change, forecast generally holding
for this evening.

Previous discussion...

Return of moisture slowly occurring across the region this
evening as seen via the latest blended TPW and PWATS off soundings
just south of the area. This in advance of a fast moving upper
disturbance across the Midwest this evening per latest water
vapor loop. Some of this moisture from spreading out of afternoon
cumulus remains stuck under the inversion aloft this evening with
even a few sprinkles showing up across the far western I-81
corridor. Although not expecting too much eastward progression of
any light showers, will include a shower or sprinkle mention for
an hour or two to start late this evening.

Otherwise main inbound axis of deeper moisture likely to fade
upon arrival into the drier air aloft after loss of heating late
tonight as evidenced by latest drier solutions. However likely
best to keep some low end pops going late tonight as the NCAR
Cam ensemble shows some light showers far west late and perhaps
jumping the Blue Ridge early in the morning. Otherwise beefing up
clouds over the west and central overnight with partly cloudy to
clear elsewhere. Also bumped up lows a little given slightly
higher dewpoints southeast, and earlier arrival of strato-cu over
parts of the mountains, but still mainly 50s overall by daybreak.

Previous discussion as of 230 PM EDT Monday...

Daytime cumulus clouds should give way to mostly clear to clear
skies this evening. However, the approach of an upper level
disturbance will start to bring a return of cloud cover to the
area after midnight tonight, and conditions will remain mostly
cloudy to cloudy through the day on Tuesday.

Isolated showers may reach the far western sections of the area by
late tonight, but chances will increase during the day Tuesday. The
best potential for showers and storms will extend from roughly
Lewisburg, WV to Bluefield, WV to Marion, VA to Boone, NC. East of
this region, precipitation in the form of isolated showers will be
more likely, east to roughly a Lynchburg, VA to Reidsville, NC line
during the afternoon.

Temperatures will continue to be on the cool side for this time of
year. Lows tonight will range from the upper 40s to the lower 50s
across the mountains and the mid to upper 50s across the Piedmont.
High temperatures on Tuesday will range from around 70 to the lower
70s across the mountains to the mid to upper 70s across the Piedmont.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
As of 240 PM EDT Monday...

At 00z Wednesday (8 pm EDT Tuesday)...the axis of an upper level
trof will be exiting our forecast area and any lingering mountain
showers will have ended. With a large area of high pressure settling
over the region...morning lows Wednesday will be well below normal
and went a few degrees below guidance. The COOP MOS guidance is
forecasting lows in the upper 30s at Burkes Garden.

High pressure continues to influence our weather on Wednesday. With
limited mixing...leaned toward the cooler guidance for highs which
should range form the lower 70s in the mountains of NW NC to the
lower 80s in the NC/VA Piedmonts.

The transition to higher humidity levels and warmer temperatures
begins Wednesday night into Thursday as higher low level theta-e air
lifts north into the region as a deepening west/southwest flow
arrives. Most the area will remain dry on Thursday, but a few
showers cannot be ruled out in the southern Blue Ridge of NW NC and
far southwest VA on the nose of a low level theta-e ridge,
increasing PWATs and differiental mountain heating. With
downsloping winds, pushed high temps Thursday up a degree or two
from the previous forecast.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 200 PM EDT Monday...

A return to weather conditions more typical for summer are expected
during the long term period, as the long range models show good
agreement transitioning from an upper level zonal flow early in the
period to an upper trof forming somewhere around the Great Lakes and
extending south into the eastern U.S. by late in the weekend into
Monday.

This will result in increasing temperatures and humidity, as well as
an increase in storm chances. An upper level disturbance moving out
of the western Gulf of Mexico into eastern VA on Friday/Friday night
will help lead a surge in higher PWAT air our area. This higher
moisture combined with a series of upper level disturbances...with
the usual differences in timing shown in the long range
models...will help generate scattered showers and storms each day
during the long term period, especially during the peak heating in
the afternoon and early evening hours. With increasing CAPES, but
low shear through the period,a few pulse severe storms and locally
heavy rain are possible.

Warmest temperatures are expected Sunday and Monday as 850mb
forecast temps approach +20C. This may generate heat index values in
the low to mid 90s in the east.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 147 AM EDT Tuesday...

VFR through the TAF period. Expect a greater coverage in SCT to
OVC VFR mid-level cloudiness from west to east through 12z with
moisture on the increase ahead of a mid-level disturbance now
making its way across the eastern Great Lakes. Given how dry
today was across the region, prospect for radiation fog at the
TAFs is very low - the best chance may be at Danville where
slightly higher surface moisture exists, though confidence is
too low to mention in the TAF at this point. Should see winds
light westerly to calm.

For Tuesday, aforementioned mid-level disturbance moves east-
southeast across the airspace. Expect mid-level clouds
persisting until mid-afternoon with a few cumulus developing
underneath these. Some showers or sprinkles possible through the
first half of the day, but well-mixed boundary layer progged by
most model guidance suggests that visibilities in showers
likely > 6 SM. Winds west 4-8 kts with gusts to 17kts. Expect
clearing to occur by late afternoon and into the evening hours
with high pressure ridge building into the region. Though winds
should also gradually abate, there still should be enough of a
northwesterly wind between 00-06z to limit any fog development
to after 06z Wednesday.

Extended Aviation Discussion...

Expect VFR conditions with a limited potential for IFR to LIFR
overnight radiation fog after 06z Wednesday. Confidence in
development currently low but a better chance of occurrence if
wetting rain affects any of the airports Tuesday.

VFR conditions then anticipated until Friday, with potential for
overnight IFR to LIFR radiation fog Wednesday and Thursday
evenings.

Friday into Saturday, the potential for sub-VFR conditions
increase as showers and storms become more numerous. Saturday
appears to feature a greater coverage of showers and storms
associated with a cold frontal passage. Likewise, an increase
in the boundary layer moisture will also lend itself to better
chances of late night/early morning patchy fog.

&&

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

&&

$$
SYNOPSIS...DS/JH
NEAR TERM...AL/JH
SHORT TERM...PH
LONG TERM...PH
AVIATION...AL/DS


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