Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 281656
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1256 PM EDT Thu Jul 28 2016

.SYNOPSIS...
Low pressure will move along a stalled front from the mid
Mississippi Valley to the Ohio Valley today and tonight. This wavy
frontal system will remain across the region through Monday. The
front is expected to drift south and dissipate next Tuesday and
Wednesday.

&&

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

Expect no significant changes to the forecast through the
remainder of the afternoon. Isolated to scattered convection is
expected to start to develop within the hour across primarily
the mountains. After roughly 400 PM or 500 PM a more organized
band of showers and storms is expected to progress into the area
from the west and make progress eastward through the evening.
Forecast highs are on track for most areas. Added a degree or two
to the forecast highs around the Roanoke region based upon the
latest observations.

As of 1215 PM EDT Thursday...

Have decided to hoist a Flash Flood Watch for our southeast West
Virginia counties and Tazewell County Virginia. Latest one hour
flash flood guidance values for parts of these counties is in the
one to one and one-half inch range. These values will be
obtainable from late this afternoon into tonight with the
potential of multiple thunderstorms training across the same
location.

As of 1020 AM EDT Thursday...

Adjustments to the forecast for this afternoon will reflect a
slightly slower arrival time of the main band of showers and
storms that will enter the region from the west. While isolated
to scattered coverage of showers and storms are expected across
the mountains starting around noon, the main swath of potentially
strong storms is more likely going to arrive in the west closer to
400-500 PM EDT and spread eastward into the evening hours.

The storm prediction center has expanded the Slight Risk for today farther
west into southeast West Virginia. If severe weather is to occur,
the greatest potential will be damaging winds rather than large
hail.

Will continue to monitor and assess any potential for flash flood
watches for any portion of the forecast area. The latest guidance
suggests portions of southeast West Virginia may have the best
potential.

As of 430 AM EDT Thursday

Cluster of showers and thunderstorms was tracking northeast through
western part of the county warning area at 400AM. High resolution
guidance has a majority of this precipitation north of the forecast
area at 13Z/9AM. There will be some residual cloud cover this
morning which will cut back on the potential heating and
instability. Temperatures will still climb into the 80s today in the
mountains and into the 90s in the piedmont. Starting with muggy
conditions this morning in part due to surface dew points in the
upper 60s to lower 70s. Heat index will top out around 100 in the
east of the Blue Ridge this afternoon but will fall short of advisory
level values.

Short waves over the mid Mississippi valley early this morning are
forecast to track into the Ohio Valley by Friday morning. This will
provide better synoptic scale lift plus forecast area will be in the
right entrance region of the upper jet this afternoon and evening.
low and mid level winds increase from the southwest to west by late
this afternoon which will increase the helicity. Bufkit forecast
soundings were showing some decent speed shear. Directional shear
becomes stronger this afternoon too as the surface low that was over
southeast Missouri this morning moves east and backs the surface
winds to the southeast.

Once the short wave moves east...surface through mid level winds
turn to the northwest and best lift will be confined to the western
county warning area. No change in air mass overnight so minimum
temperatures will be similar to past few mornings.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 330 AM EDT THURSDAY...

A shallow slow moving upper trof will remain across the eastern part of
the country through the weekend. This will keep a steady stream of
short waves moving through the region, along with deep moisture and a
lingering frontal boundary just off to our southeast. This pattern will
produce broad synoptic lift and enhance convective activity that
develops in the unstable environment, and give us increasing chances
for showers and thunderstorms each day through the weekend with the
best chances mainly along and west of the Blue Ridge. Shear will be
limited so any marginal severe threat will be with pulse
storms/clusters, and the concern for hydro issues will be growing as
successive rounds of locally heavy rain will start to add up.

Temperatures will be right around normal for late July with highs
generally around 90 east of the Ridge, low/mid 80s west.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 1150 AM EDT Thursday...

Belt of westerlies will be laying across the area Sunday night into
Monday, with front situated across the mid-Atlantic. Afterward the
upper flow takes on a more NW to SE orientation across our area as
ridge builds over the Central Plains. The front weakens but
convergence along it to remain through midweek. In addition, the
upper pattern favors potential ridge runners, where convective
clusters form over the upper midwest and shift southeast over our
area.

Overall, will keep threat of showers and storms in the forecast all
periods but looks like Sunday-Monday have the better chance for
measurable rainfall.

May see slight nudge downward in temps early but overall humidity
levels should stay the same, so no appreciable dry air expected
thru Thursday.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 745 AM EDT Thursday...

Lingering LIFR clouds and fog at KLWB and in the western
Appalachian mountains this morning will dissipate by 14z/10AM.

Storms will develop over the mountains during the early afternoon
and then move east into the foothills and piedmont during the mid-
late afternoon. High confidence of a couple hours of MVFR
conditions due to the storms at all the airports in the central
Appalachians but timing is still uncertain. Bufkit showed a
favorable shear profile for more organized storms and the
potential for microburst winds within the thunderstorm cores
leading to isolated surface gusts of 30-50kts.

Coverage of thunderstorms will diminish after sunset in the
piedmont. Scattered showers will continue in the mountains
overnight. Models bring in IFR ceilings with deep westerly winds
after 06Z/2AM in the western mountains. Have added this with
medium confidence of occurrence.

Extended aviation discussion...

An upper ridge of high pressure will remain just south of the
area and a residual frontal boundary will remain over the area through
Monday. This will allow for periodic, mainly diurnally
driven, deep convection. A more widespread sub-VFR potential
exists into Friday per a strong wave of low pressure which will
ripple east along a stalled front. After the passage of this
wave, some decrease in coverage of precipiation is expected over
the weekend. In addition to the thunderstorm threat, late night
and early morning fog will likely occur at the usual valley
locations.

&&

.CLIMATE...
Record warm minimum temperatures for July 28

Bluefield WV.....69 in 2010
Danville VA......76 in 1997
Lynchburg VA.....77 in 1930
Roanoke VA.......80 in 1930
Blacksburg VA....68 in 1987

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flash Flood Watch from 4 PM EDT this afternoon through Friday
     morning for VAZ007.
NC...None.
WV...Flash Flood Watch from 4 PM EDT this afternoon through Friday
     morning for WVZ042>044-507-508.

&&

$$
SYNOPSIS...AMS
NEAR TERM...AMS/DS/WP
SHORT TERM...MBS
LONG TERM...WP
AVIATION...AMS/PM
CLIMATE...PM



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