Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
issued by National Weather Service Raleigh NC
115 PM EDT Tuesday Jul 7 2015
a cold front approaches from the northwest tonight. The front is
expected to stall just north of the region by Wednesday...then
lift back north as a warm front late in the week...as high
pressure aloft builds across the southeast states.
Near term /through tonight/...
as of 1012 am EDT Tuesday...
Valley fog beginning to burn off...although taking a bit longer
than usual. Latest hrrr suggests it will be gone within the next
hour or so. Otherwise...current forecast in good shape with no
changes for the morning update.
Today will be our drier of the next few days as we are between
impulses in the upper levels. Still not a 100 percent chance of
dry...as there will be some weak convergence in the mountains aided
by differential heating...to allow for some pop up storms. At this
time...the best chances will be along and west of Interstate 77 and
more into WV/far SW Virginia into Kentucky. A very warm day since more sunshine
is expected with SW flow and building heights. Previous forecast of
middle 80s west to lower 90s east looks good.
Tonight...a frontal boundary will sag southeast toward the upper
Ohio Valley into Kentucky and models are keeping the majority of the
forecast area dry with the active weather staying in a region from
Missouri to western PA. Still convective outflows ahead of this activity
may work into the mountains of WV overnight...so kept higher probability of precipitation over
the Greenbrier valley...with slight chance as far east as the
Shenandoah Valley to NC mountains muggy lows expected with middle to upper
60s mountains...to lower 70s east.
Short term /Wednesday through Friday night/...
as of 330 am EDT Tuesday...
Upper level ridging across the southeast states will build west
along the Gulf Coast on Wednesday...allowing for increasingly zonal
flow across the middle Atlantic. The building ridge will help keep an
approaching cold front north of our area for Wednesday afternoon and
evening...causing it to stall near the Ohio River. Regardless...
still sufficient instability associated with a passing upper level
disturbance riding along the front to trigger widely scattered
thunderstorms during late afternoon and evening...with rain chances
highest near the Interstate 64 corridor. Instability parameters are
modest for the most part...but indicate enough cape and low level
shear to trigger a few strong to severe storms...capable of
producing hail and locally strong winds.
The front will drift northward on Thursday as yet another low
pressure system passes just south of the Great Lakes...and expect
minimal shower and thunderstorm activity for much of the day. Rain
chance will increase during the evening however as the low pushes
east for the Upper Middle Atlantic...dragging a cold front southward
toward our region. Best rain chances will be across the western
slopes...with northwesterly downslope windflow further east causing
showers and thunderstorms to break up.
The cold front will pass across our are Thursday night...and stall
just to our south for Friday. Will have to keep an eye to our
northwest for any approaching disturbances as the center of upper
level ridging shifts to the lower Mississippi River valley...shift
upper level winds across the middle Atlantic from the northwest.
With our area south of the front on Wednesday Thursday...expect
afternoon highs to range from the low/middle 80s across the
mountains...to the upper 80s/low 90s across the Piedmont. Frontal
passage Thursday night will knock off a few degrees for highs on
Friday...ranging from low 80s west to low 90s east. Overnight lows
will range from the middle 60s to the low 70s.
Long term /Saturday through Monday/...
as of 200 PM EDT Monday...
Models are in agreement the subtropical ridge that builds over the
southeast states for middle/late week will retrograde toward
Texas/Oklahoma for the weekend then expand northwest into The
Rockies for the first part of next week...July 13-17. Short wave
energy which will initially traverse the northern tier states this
week with an active frontal zone to our north...will begin to track
farther south over the weekend as the upper ridge wanes over the
eastern Continental U.S.. as troughing aloft increases...expect frontal
boundary to drift south over the region providing a better
opportunity for showers/storms in addition to more cloud cover and
lower daytime high temperatures.
Have not been able to identify any given day where we could
completely remove threat for showers/storms...thus entire extended
period of the forecast will reflect daily chance of showers.
Temperatures...although nothing extreme...will favor the warm side
of guidance this weekend...then retreat to something near or just
below normal for the start of the following week.
Aviation /17z Tuesday through Saturday/...
as of 115 PM EDT Tuesday...
VFR expected through the rest of this afternoon with cumulus and
stratocu in vicinity of the higher terrain. Showers/thunderstorms across eastern Kentucky and
northern/western WV are prognosticated to weaken as they move east...so for now
have kept them out of the tafs. As the front moves closer tonight
and ealry Wednesday...the risk for rain and sub-VFR conditions will
increase...especially at blf and lwb.
Extended aviation discussion...
A cold front will stall near the WV/Maryland border west to Ohio by Wednesday.
South of this boundary...we will remain on the warm/moist side of
the front...and subject to daily threat for MVFR showers/storms.
Expect widespread late night/early morning low clouds/fog with
IFR-LIFR cigs/vsbys. Overall...conditions should improve to MVFR-
VFR outside rain showers/thunderstorms and rain activity during the afternoons.