Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
200 am EDT Tuesday may 5 2015
high pressure will remain centered over the coast of the Carolinas
through most of this week. A back door cold front will head south
into the region by Wednesday. An area of low pressure is expected to
form off the coast of Florida by the middle of the week...and then
late this week into the weekend...track onshore through the
Near term /through today/...
as of 1125 PM EDT Monday...
Anticipate a quiet weather night with a few clouds arriving into the
the mountains by dawn...but still mainly clear. Updated grids
reflect some patchy river fog in the New River valley by dawn.
Low temperatures will be in the middle to upper 40s deeper valleys with 50s
Previous valid discussion from 4pm Monday...
On Tuesday...both temperatures and low level moisture content will
be greater than what was experienced Monday. We are expecting
another day of afternoon shower development with increased cloudy
cover. Coverage is expected to be scattered across the
mountains...with isolated thunderstorms a greater potential.
Coverage will be isolated just east of the crest of the
Blue Ridge...east to a line from roughly Lynchburg Virginia to
Yadkinville NC. High temperatures will be a little warmer than
those of Monday. Expect middle 70s to near 80 across the mountains
with low to middle 80s across the Piedmont.
Short term /tonight through Thursday night/...
as of 330 PM EDT Monday...
Similar to previous nights...shower activity and cloud cover will
diminish Tuesday evening with the loss of daytime heating...making
for mostly clear skies after midnight. May see a few pockets of fog
develop...mainly across areas where significant rainfall occurred on
Tuesday afternoon/evening. Overnight lows will fall into the low to
Rainfall coverage will be more widespread on Wednesday as high
pressure moves across the Great Lakes...pushing a cold front
southward across the middle Atlantic. Exact timing of the frontal
passage through our area is still in question...but latest model
guidance suggests that the front will pass through during the
afternoon and evening. Convergence ahead of the front will offer
enough support for scattered showers...with a few thunderstorms
during late afternoon into the evening. A few storms may become
strong...but believe severe thunderstorm activity will be isolated
at best. Deeper moisture will pool ahead of the front however...
pushing precipitable water values to 1.1 inches mountains to 1.4
inches Piedmont. And with light steering winds expected...believe a
few showers/storms will be capable of producing locally heavy rain.
Expect highs to range from the middle/upper 70s for the mountains...to
the middle 80s across the Southside.
High pressure will build into the area Wednesday night with the
passage of the cold front...turning winds across our area easterly
for Thursday. Much of the time...the high pressure wedge and
easterly wind shift would result in significantly cooler
temperatures for the middle Atlantic. However...upper level ridging
across the east will counteract the easterly flow...shaving off
only a few degrees for Thursday afternoon highs compared to
Wednesday. High pressure will provide more stability however...and
expect only spotty shower activity...with perhaps one or two
thunderstorms during the evening.
Long term /Friday through Monday/...
as of 345 PM EDT Monday...
Models are coming into better agreement that a tropical low riding
north from the Caribbean will move onshore somewhere along the South
Carolina coast Thursday evening. The main impact for our area would
be an increase of deeper moisture heading through the weekend...
which would in turn support locally heavy rain in some of the
showers and thunderstorms that develop each afternoon and evening
with daytime heating. Upper level winds will remain light through
the weekend...indicating that any showers and thunderstorms will be
slow moving. Afternoon highs will range from the middle 70s west to the
low 80s east each day...while overnight lows will be in the upper
50s to low 60s.
Aviation /06z Tuesday through Saturday/...
as of 200 am EDT Tuesday
VFR ceilings expected through the taf valid period.
Some patchy fog possible in the New River valley early this
morning between bcb-mkj...otherwise no visibility restrictions.
Daytime heating will result in cloud build-ups after 14utc/10am
with widely scattered -shra and isolated thunderstorms across the
mountains Tuesday afternoon courtesy of daytime heating and weak
convergence across the higher terrain. Still not enough coverage
to have in prevailing group but enough to have vcsh at roa/bcb/blf
where somewhat greater threat exists.
As the low levels moisten up we have to watch for the development of
fog at night/early morning over some of our taf sites...such as
bcb/lwb...but not enough confidence to begin adding to the taf
sites at this time.
Medium to high confidence in all taf parameters this period.
Extended aviation discussion...
Showers and thunderstorms will be more numerous on Wednesday and
Thursday as a back door front enters the region from the northeast.
Extended periods of sub-VFR ceilings/visibilities appear unlikely this week...but
morning fog will become an increasing issue...especially the
mountain valleys vicinity of kbcb and klwb. Winds overall will be on
the light side through the week. Exception will be vicinity of
rain showers/thunderstorms and rain where downdraft gusts may approach 25 kts.