Area Forecast Discussion
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FXUS61 KRNK 310117
Area Forecast Discussion
National Weather Service Blacksburg VA
917 PM EDT Sat Jul 30 2016
Low pressure will drift east passing north of the area overnight
into later Sunday. A cold front with this feature will move to
the Central Appalachians by Sunday night. Monday into Wednesday
the low will be offshore with the front extending into the
.NEAR TERM /THROUGH SUNDAY/...
As of 900 PM EDT Saturday...
Surface trough axis trailing the shortwave passing well to the
north has been the main focus out east this evening where deeper
instability has coincided with better supports/winds aloft to
result in isolated deep convection. Latest analysis shows this
feature slowly swinging east but given leftover 1-2K CAPE and
stronger westerly unidirectional flow off evening soundings may
continue to see bands redevelop out east until around midnight.
Also spotty showers possible elsewhere given outflow and soupy
dewpoints so leaving in some low pops before tapering around
midnight. Next upstream wave looks to push east late tonight with
added showers possible mainly western third late as seen with
cloud cover off earlier models and isolated shower potential off
the latest HRRR. Otherwise mainly partly cloudy and very muggy
again with patchy fog espcly east where rain has occurred and
across the mountain valleys. Left temps similar to previous with
most in the east staying the 70s with 65-70 west.
Previous discussion as of 325 PM EDT Saturday...
Mesoanalysis this afternoon showing best moisture convergence along a
line from near Raleigh north toward the Shenandoah Valley. Radar
showing scattered showers and storms across the Blue Ridge from the
NC foothills northeast toward Amherst and more isolated west.
As we head into the evening, models are favoring the piedmont with
more coverage which is in step with sfc analysis. Still looking at
high chance pops north and northeast to lower in the south and
southwest. There is some upper level energy back over middle TN this
afternoon that slowly moves east toward the mountains late tonight.
So for now will have some break in the showers and storms after
midnight then increase pops from the southwest toward morning though
the coverage may lessen given time of day being unfavorable.
Sunday, the main belt of westerlies stays over the northern CWA with
a lee trough developing at the sfc over the Piedmont. Nothing really
to latch onto but watching upper impulses and timing them. Models
are favoring a better threat of storms along/near the Blue Ridge
Sunday afternoon spreading east to southeast to the piedmont. Will
have pops in the high chance to low likely range by late afternoon.
Lows tonight will range from the mid 60s west to lower 70s east,
then rise to the lower 80s west for highs Sunday to around 90 east.
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
as of 300 PM EDT Saturday...
Low amplitude trough will continue to affect the eastern CONUS from
the Great Lakes into New England over the next few days. Several
spokes of short-wave energy will be rotating through this trough in
a fairly chaotic fashion with various model solutions as to strength
and timing. Models agree that an associated frontal boundary will be
dropping southeast across the forecast area Sunday night into
Monday. Not expecting much in the way of sensible weather with this
feature but may become a focus for showers and thunderstorms later
in the day Monday as heating/destabilization takes place with the
best chances for convection focused across the southern sections of
the CWA. Slightly drier and cooler air will filter southward behind
this front with highs Monday about normal for the first day of
August. Tuesday looks to be mostly dry as the front is to our south
and high pressure over located over the northern mid-Atlantic will
provide weak northerly flow at the surface. Still maintained slight
chance pops with diurnal heating cycle but not expecting much
activity. Highs again near early August climo although slightly
drier air should make it a tad more pleasant.
.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 300 PM EST Saturday...
Surface high will drift slowly northeast Wed-Thu as upper heights
begin to rise again. The boundary over the Carolinas will more or
less undergo frontolysis by Thursday leaving most of the mid-
Atlantic region back in a familiar pattern; daily thunderstorm
chances and near seasonable warm and humid conditions. Mesoscale
features and subtle short-waves will regulate the favored areas for
convection within the diurnal heating cycle unless a stronger short-
wave is able to maintain overnight activity but not really possible
to pin down anything at this longer range. We remain near the summer
climatological maxima for temps but the slow downward trend will
commence only a few days after this extended forecast period ends.
.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
As of 700 PM EDT Saturday...
Widely scattered shra/tsra look to persist into this evening with
best coverage mainly north and east of the taf locations. Since
still cant rule out an isolated shower or storm popping up in the
next hour or two, maintained a vicinity mention at most spots
until a while after loss of heating. Some added showers may move
into the west or persist across the far northeast sections into
the overnight but too uncertain to include any mention after
better instability wanes. Otherwise looking at fog potential at
most sites, but more likely KLWB/KBCB where IFR vsbys to LIFR
After fog/stratus burns off 14z/10am Sunday, looking at VFR into
midday although some lingering mid deck and isolated showers
possible, with more storms developing around or after 18z/2pm.
Coverage looks a bit more widespread with possible development
over the mountains just ahead of the front early on, with
progression east of coverage into the eastern lee trough later in
the afternoon. However given uncertainty will basically include a
VCTS or VCSH Sunday afternoon at most locations at this point.
Convection should again fade out Sunday evening with more
widespread fog/stratus and sub-VFR likely after midnight espcly
where earlier showers occurred.
Extended aviation discussion...
The weak cold front will sag through the region later Monday
before stalling just south of the area into midweek. This should
briefly push deeper moisture to the south to start the week with
mainly isolated convection Monday and perhaps mainly south/east
of the taf sites Tuesday into Wednesday. Moisture will return
north by Thursday ahead of the next upstream cold front with
shra/tsra likely increasing Thursday afternoon. Thus VFR
conditions are expected for most of the time, with the exception
being temporary sub-VFR conditions under any shower or
thunderstorm, and during the night with patchy fog and stratus
over parts of the region.