Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
718 PM EDT Monday may 4 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 Tuesday/...
as of 550 PM EDT Monday...
Quick update to Orient probability of precipitation a little closer to radar and latest
model trends. Also not getting any vertical development and
removed thunder from the forecast. Minor tweak to sky cover as
well to reflect Sat trends.
Previous forecast discussion at 4pm...
High pressure remains situated off the coast of the Carolinas. Flow
around associated ridge axis is bringing weak onshore flow is
westward through the GA/SC. The flow then veers southwest with
the Atlantic moisture reaching the southwest portion of the
forecast area. This moisture along with differential heating and
orographical influence is helping to generate some isolated
showers along the crest of the Blue Ridge from roughly Floyd
Virginia...southwest into the northern mountains of North
Carolina. This trend will continue the remainder of the
afternoon...with the activity quickly dissipating with the
approach and arrival of sunset.
Tonight...the cloud cover associated with the afternoon convection
will likewise not survive too long into the overnight hours.
Anticipate most areas to be mostly clear to clear by midnight. With
increasing southwesterly flow...anticipate higher dew point air to
advect into the region tonight as compared to conditions realized
this morning. Likewise...the forecast low temperatures will be
milder than those of last night. A mix of low to middle 50s are
expected across the mountains with middle to upper 50s across the
On Tuesday...both temperatures and low level moisture content will
be greater than what was experienced today. We are expecting another
day of afternoon shower development with increased cover than what
we are experiencing today. Coverage is expected to be scattered
across the mountains...with isolated thunderstorms a greater
potential than today. Coverage will be isolated just east of the
crest of the ridge...east to a line from roughly Lynchburg Virginia to
Yadkinville NC. High temperatures will be a little warmer than those
of today. Expect middle 70s to near 80 across the mountains with low to
middle 80s across the Piedmont.
Short term /Tuesday night 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 /23z Monday through Saturday/...
as of 712 PM EDT Monday
VFR ceilings expected through the taf valid period.
Any showers early this evening southwest of hlx to along the Blue
Ridge will fade with loss of heating.
There will be another threat of scattered rain showers and isolated
thunderstorms Tuesday afternoon with weak convergence around the
higher terrain. Still not enough coverage to have in prevailing
group but enough to have vcsh at roa/bcb/blf where the greater
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 tonight to add.
High confidence in all taf parameters this period.
Extended aviation discussion...
Scattered showers and thunderstorms are expected to persist along
the southern Blue Ridge into Tuesday evening...producing localized
MVFR/IFR conditions within the rain shafts.
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 throughout the week at
the usual spots...klyh/kdan/kbcb/klwb. Winds overall will be on
the light side through the week.