Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
155 am EDT Monday Jul 28 2014
upper disturbances will continue to work across the area this
evening in advance of a strong cold front that will be
arriving from the northwest after midnight. These features may
trigger strong to potentially severe thunderstorms into early
tonight. The cold front will move across the region by early
Monday...resulting in cooler weather into the middle of the work
Near term /through today/...
as of 115 am EDT Monday...
Convection approaching from West Virginia has weakened over the
past few hours...amounting only to shower activity at this time.
See no need to prolong the Tornado Watch...and have therefore
cancelled it early for the mountain Empire through the Shenandoah
Valley. Adjusted rain chances for the next few hours based on
radar trends and hrrr model data which appears to be handling the
current rainfall very well. Expect only spotty upslope showers
should be all that remain by sunrise.
Latest surface observations indicate the cold front is situated
near the Ohio River...progressing a little slower than previously
forecast. Expect the front to enter our southeast West Virginia
counties by around 5 am...and then continue east through the
As of 200 PM EDT Sunday...
500 mb trough crosses east of the area Monday allowing high pressure to
start building in from the west during the afternoon. However
another shortwave rounding down the back of the cool pool may help
to enhance the showers as it coincides with the coldest 850 mb temperatures
and maximum heating. Thus boosted probability of precipitation western slopes to a period of
low likelys Monday afternoon with a quick cutoff to rain showers Blue
Ridge and points east where downsloping should allow for less
clouds. Odor will be a breezy and cool day for late July over the
mountains where may struggle to get out of the 60s where clouds
persist and along higher elevations. Should be able to get well
into the 80s under dry downslope Piedmont but only 75-82 Blue
Short term /tonight through Wednesday night/...
as of 215 PM EDT Saturday...
West to northwest upper flow will persist over the Blacksburg
forecast area through the short term period as series of weak short
wave troughs embedded in upper flow help anchor pin-Wheeling upper
trough over the Great Lakes.
Cooler air aloft...weak forcing from initial short wave...and weak
upsloping may support isolated to widely scattered showers across
the western flanks of the Appalachians on Monday night...and perhaps
diurnally driven even into Tuesday. However...despite additional
weak stream energy...arrival of surface ridge and amplification of
subsidence inversion should be sufficient to limit threat for any
additional shower activity Tuesday night through Wednesday night.
Upsloping clouds across the west should maintain unseasonably cool
temperatures in the mountains...with daytime highs not likely to
climb out of the 60s on either Tuesday or Wednesday across the
highest terrain. East of the Blue Ridge...any influence of cold
advection will be offset by downsloping/compressional heating and
good insolation such that highs reach into the lower to middle
80s...yet still ~5f lower than climatological averages.
Nighttime lows will be largely governed by extent of mixing and
cloud cover. Higher elevations where/if clouds can clear...and
especially the mountain valleys where boundary layer decoupling will
more readily occur...should experience at least spotty readings down
into the 40s. Readings east of the Blue Ridge will be a bit
milder...mainly 50s...yet still 5-10f below climatological averages.
Long term /Thursday through Sunday/...
as of 1200 PM EDT Sunday...
A surface high Thursday over southern Michigan will shift east
towards New England by Friday and Saturday. At the middle levels a
persistent trough is set up over the eastern US with a ridge over
the western US. Thursday lacks low and middle level moisture so expect
the day to be dry. Moisture and instability increase for Friday and
through the rest of the period as several disturbances pivot across
the region around the base of the trough. Expect scattered showers
and thunderstorms to develop each afternoon/evening and taper off to
just scattered showers during the evening. Focus of the highest
chance probability of precipitation are over the mountains where the best convergence will
be located...with lower chance probability of precipitation out east.
Thursday will be the warmest day of the period with 850mb temperatures
around +16c. This will correspond to surface high temperatures in the middle
80s out east and near 80 across the mountains. As the high shifts
east on Friday the winds will shift from north/northwest to an easterly
direction. This will wedge the area in through the remainder of the
period. With the increased low/middle level moisture expect cloudy
conditions. This along with expected scattered precipitation and 850mb
temperatures falling to +11-14c...surface high temperatures will be 5-10 degrees
below normal Friday through Sunday.
Aviation /06z Monday through Friday/...
as of 150 am EDT Monday...
Keeping an eye on the last of the convection entering the mountain
Empire this morning...breaking up as it begins to move downslope
east of the highest ridges. May see brief gusty winds at blf as
Showers Pass...drawing stronger winds aloft to the surface.
Showers will exit by 08z...and expect only isolated development
thereafter along the western ridges.
The cold front is making its way across WV and will enter the
vicinity of klwb/kblf by around 09z...and progress east quickly
through the morning. Westerly downslope winds will maintain VFR
conditions for kroa/klyh/kdan east of the Blue Ridge while
lingering stratocu will result in patchy MVFR ceilings for a few
hours before sunrise for kbcb/klwb/kblf.
Through the day...energy rotating through the upper trough will
combine with upslope and instability below the subsidence
inversion and steepish lapse rates as seen on model soundings to
squeeze out a few sprinkles at klwb and kblf by late afternoon.
Winds look to be gusty through the first part of the taf as 850mb
flow is zipping along and downward momentum Transfer should be
efficient to mix it down after daybreak. The latter portion of the
taf period looks quiet with VFR east of the ridge and MVFR west
and winds settle down toward evening before decoupling.
Extended aviation discussion...
drier air pushing in for Tuesday-Wednesday will bring mainly VFR
conditions...but cannot rule out late night fog at kbcb/klwb...
although the low levels may stay dry enough for less fog coverage.
Variable ceilings expected under anomalous upper low throughout the
rest of the week. A few -shra not completely out of the question
across eastern WV...along with occasional MVFR ceilings. Typical fog
potential less than normal for this time of year throughout the
week because of turbulent mixing and prevailing cyclonic flow.
Toward the end of the week...as the upper low retrogrades just
west of the region...increasing potential for rain showers/thunderstorms and rain but mainly
SW of the taf sites into Friday.
the weather radio at Hinton West Virginia transmitting on frequency
162.425 mhz remains off the air likely due to phone line problems.
Restoration of service is not expected before noon on Monday.