Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Blacksburg Virginia
330 am EDT Fri Aug 23 2019
a cold front moves south into the region today and tonight. By
Saturday, the front will extend from the Carolinas to the
Southern Plains. Cooler high pressure will build into the mid
Atlantic region Sunday and Monday.
Near term /through tonight/...
as of 320 am EDT Friday...
Latest rap guidance was showing a pocket of relatively higher convective available potential energy
from Wilkes County to Patrick County through 6am. Expect the line of
showers and thunderstorms to continue northeast through Patrick and
Stokes County then begin to weaken.
Southwest Virginia, northwest North Carolina and southeast west
virgina will be in the right entrance region of a 110 knot upper jet
today. Slightly stronger winds through mid levels of the atmosphere
will led to higher bulk shear today which would support bowing lines
and segments. Amount of instability will be the liming factor today
in determining the location of the strongest storms. Morning showers
and thunderstorms will weaken as they move northeast but may leave
enough cloud cover over the mountains to hamper heating in the
morning. Better convective available potential energy will be in the
Piedmont of Virginia and North Carolina. 3km NAM showed 2000 j/kg
this afternoon in Danville. Will continue to include heavy rain in
the forecast ahead of the front, due in part to efficient warm rain
processes and precipitable water values closing in on two inches.
NAM and GFS were in good agreement with the timing of the surface
front today and tonight. The 850mb front reaches the Virginia/North
Carolina border just after 00z/8pm with 850mb temperatures north of
the front lowering into the +12 to +16 range by morning. Mid and
upper levels of the atmosphere dry overnight but low level moisture
will remain. May lower minimum temperatures for tonight slightly
across the Virginia Piedmont and the North Carolina foothills and
Piedmont, otherwise no major changes planned.
Short term /Saturday through Monday/...
as of 300 am EDT Friday...
Increasing confidence that the weekend into early next week will
feature abundant cloud cover with cooler than normal (comfortable)
temperatures, lowered humidity levels and modest easterly breezes.
Periods of light showers mainly to our southern third of the
forecast area and against the Blue Ridge, becoming more intermittent
moving through the period.
Cold front, to be roughly positioned near the Virginia/NC border to open
Saturday, is expected to trudge slowly southward into central NC
through Saturday/Saturday night. Its presence near our NC counties
into Southside will offer the potential for lingering light showers
for these areas. Increasingly though, northeast to easterly flow
associated with a high pressure wedge nosing southward on the
northern end of the cold front will take hold of the region's
weather. Even into Virginia, a considerable amount of low-level
cloudiness looks likely. This will lead to temperatures running
below typical late-August normals. Met-based MOS guidance is quite
cool on the highs, in the 60s to lower 70s which are in the ballpark
of daily record low maximum temps. Won't go quite that low, but will
show lows ranging from the upper 60s to the mid 70s. Still some
lingering slight to low chance pops for Saturday night across our
northern NC counties, with lows in the mid 50s to lower 60s.
By Sunday into Monday, easterly winds become enhanced as strong
wedge interacts with an area of disturbed weather off the southeast
U.S. Coast. NHC is currently monitoring this distant coastal system
for possible tropical development; for the latest on this system,
please refer to the latest statements from the National Hurricane
Center. Models show this coastal low pressure circulation mainly
affecting coastal waters; its net effect for our area will be an
increase in northeast/east winds and drawing low-level moisture and
clouds back westward. We should see weather conditions that should
resemble what we often find with wedges: lots of clouds with high
temperatures on the lower end of temperature guidance. Best chances
for light rain showers are on the east-facing slopes of the Blue
Ridge into the adjacent foothills and Piedmont of NC, but the
coverage will be pretty spotty and intermittent. Highs on Sunday
only look to top out in the low to mid 70s, and only a few degrees
warmer than that by Monday.
Long term /Monday night through Thursday/...
as of 300 PM EDT Thursday...
A much cooler and drier period appears to be in store for the
into early next week. Highs will be 10 to 15 below what has
recently been experienced with daily highs in the 70s or even
upper 60s and overnight lows will be 50s west to low 60s east.
Will certainly feel different. The surface high will shift north
and east toward mid-week with increasing southerly flow and
warmer temperatures along with renewed chances for mainly
An approaching front toward mid- to late late week will
possibly trigger a few stronger thunderstorms in an increasingly
warm and unstable air mass. A trough of low pressure currently
along the Florida coast has been given a 30 percent chance of
tropical storm formation near the SC/NC coast in the latest NHC
5- day outlook but impacts on the local weather look to be
negligible or minimal at this writing.
Aviation /08z Friday through Tuesday/...
as of 155 am EDT Friday...
Radar showed showers and thunderstorms over western north
carolin and western Virginia early this morning. Laps and msas
analysis showed modest instability from kukf to kblf. The
showers and storms will continue to move northeast but gradually
weaken through 12z/8am as they move into more stable air.
Expect patchy MVFR fog this morning, especially east of the Blue
A cold front extended from southern Pennsylvania to central
Missouri this morning. This front will sink slowly south today
and tonight. Numerous showers and thunderstorms are expected
across the mid Atlantic region and central Appalachians this
afternoon and evening. Some of the thunderstorms will have
strong gusty winds and most will have very heavy rain along with
MVFR or lower visibility.
By this evening the front will be close to the Virginia/North
Carolina border. Models showed good consensus that MVFR or lower
ceilings and fog will fill in north of the front after 00z/8pm.
Confidence was above average for showers and thunderstorms
along and ahead of the front today, but confidence on exact
timing was lower.
Confidence on ceiling and visibility conditions behind the
front tonight was average.
Extended aviation discussion...
A cold front will continue moving south through the region
Saturday, resulting in scattered to numerous thunderstorms,
mainly for southern Virginia and across North Carolina.
Improving conditions with more in the way of VFR will be
possible for Sunday, pending just how far south of the mid
Atlantic area the front progresses. Some MVFR showers are
possible in the southwest Virginia and northwest North Carolina
on Monday. Scattered showers and thunderstorms with MVFR
conditions are expected Tuesday.