Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
954 am EDT Monday may 4 2015
high pressure surface and aloft will remain centered near the
Carolina coast through Tuesday. This feature will result in mainly
fair weather with unseasonably warm temperatures through middle week.
Moisture will gradually increase per moist southwest winds...so
cannot rule out a stray shower or isolated thunderstorm during
the peak heating hours each day. A backdoor front is expected to
drop southward from New England on Wednesday...providing a better
opportunity for showers. Another feature to watch for late in the
week is an area of low pressure which is forecast to develop over
the Bahamas middle week...then drift northward to along the South
Carolina coast towards weeks end.
Near term /through tonight/...
as of 950 am EDT Monday...
No major changes to the ongoing forecast. Have only made minor
adjustments to hourly temperatures...dew points...wind and sky
cover for the remainder of the morning into the early afternoon
based upon the latest observations and expected trends.
As of 445 am EDT Monday...
In spite of a weather pattern that is becoming increasingly active
across the Continental U.S....our part of the country is pretty quiet at the
moment. High pressure surface and aloft centered near the Carolina
coast will provide another mainly fair/dry day with temperatures
climbing 5 to 10 degrees above normal. The airmass over the area
is still relatively dry...so the combination of dewpoints in the
40s and deep mixing will result in the relative humidity bottoming
out in the 25 to 30 percent range this afternoon.
Since the surface high is centered closer to the coast today
compared to yesterday...clockwise wind flow around the high will
begin to draw some moisture up along The Spine of the Blue Ridge
from the southwest. Forecast cape of 500-1000 j/kg suggest enough
moisture may be available for a few showers...isolated
thunderstorm...late afternoon...mainly southwest of
Roanoke...vicinity of the Blue Ridge Parkway from Floyd into the
mountains of North Carolina. Mean winds are pretty weak...less
than 10 kts...so anything that develops will move very little.
Inhibiting factor for anything more than isolated coverage is fact
that airmass above about 15kft is still dry...limiting deep
For tonight...mild conditions anticipated. Southwest winds will
continue the overall warming and moistening process with dewpoints
inching upward. Low temperatures most areas are expected in the
50s...and similar to last night look for scattered-broken Alto-cu.
Short term /Tuesday through Wednesday night/...
as of 400 am EDT Monday...
An upper level ridge will bring warm temperatures to the region into
Wednesday. Tuesday's temperatures likely to peak above normal with
middle to upper 70s west to lower 80s east. Being ahead of a cold front
to the north...Wednesday will be a few degrees warmer than Tuesday
unless more widespread showers drift across the area.
With an upper level ridge over the region...any showers that develop
late in the afternoon Tuesday will move slowly and not last long
past sunset. With the approach of a back door cold front Wednesday
afternoon...more areal coverage of showers are expected. Models may
be to aggressive with the frontal passage Wednesday
afternoon...especially with no strong convection developing over the
area. With the slower timing of the front across the area...will
increase probability of precipitation Wednesday evening...especially in the east as the
front wedges south across the Piedmont.
Long term /Thursday through Sunday/...
as of 335 PM EDT Sunday...
Main issue this period will be interplay between sub-tropical low
developing off of the Florida Atlantic coast and then initially
drifting north...and the position of the back door frontal boundary.
Becoming more confident that on Thursday the front will continue to
move southwestward...possibly aided by the strengthening low off the
southeast U.S. Coast. This will place a focus on any convective
development mainly across the western portion of the forecast
area...mainly west of I-77...and possibly even farther southwest if
trends continue. A little trickier in southeast WV as frontal
boundary could get hung up there or could at least still be in that
area earlier in the day...so kept a chance pop from Alleghany
Highlands south toward northwest NC foothills. This all may need to be
pulled farther toward southwest as we get closer to Thursday.
By Friday most longer range models are then shifting the low back
toward the west or stalling it...well south of US and still probably
off the coast...as pattern becomes blocked. In this position there
could actually be increasing subsidence over our region into the
weekend...perhaps with still weak convergence over mountains and at least
isolated shower activity. Think thunder chances would be limited
given this subsidence aloft...so kept thunder mention out by
Saturday and Sunday. This of course is all very dependent on where
this sub-tropical low...potentially with some tropical
characteristics...ends up drifting. So overall a fairly low
confidence forecast. While appearing less likely with all 12z model
cycles that this will drift northwestward all the way into the
southern Appalachians...this system needs to be watched closely
since a track this far north could mean significant rainfall if it
did. Such a path would also have a major influence on high temperatures by
late week into the weekend...but for now the rather warm conditions
with ridge being the dominant factor look the most likely.
Aviation /14z Monday through Friday/...
as of 800 am EDT Monday
VFR ceilings expected through the taf valid period.
There is a persistent layer of trapped middle-level moisture in the
5-10kft range underneath an pronounced inversion. This will
persist through the valid taf period with high pressure aloft
over the region. Thus...expect scattered-broken cloud bases...all cloud
elements remaining above 5kft above ground level. During the peak heating part of
the afternoon some isolated deeper convection may develop vicinity of
the Blue Ridge southwest of Roanoke...kroa...into the mountains of
North Carolina. Steering winds are light...less than 10 kts...so
expect little movement for anything that develops. While threat
for deep convection exists along Blue Ridge...the probability
remains too low to include in any of the taf sites at this time.
Medium to high confidence in cloud bases through the taf valid
period. High confidence in visibilities. Medium confidence in
wind direction and speed through the taf valid period.
Note...the visibility sensor at the ASOS at kblf continues to be
sporadically out of service. Repairs may not be possible until the
end of may. Will continue with amend not schedule appended to blf taf.
Extended aviation discussion...
Scattered afternoon and evening showers and thunderstorms are
expected along the southern Blue Ridge on Tuesday...associated
with MVFR conditions.
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...lyh/Dan/bcb/lwb. Winds overall will be on the
light side through the week.
as of 200 am EDT Monday...
The visibility sensor at the Bluefield...kblf ASOS...is
experiencing intermittent outages.