Scientific Forecaster Discussion
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Area forecast discussion...updated
National Weather Service Blacksburg Virginia
1151 PM EDT sun Jun 16 2019
a wavy front will drift across the Ohio Valley and mid Atlantic
region through Monday. Low pressure tracks east along the front
Thursday and Friday. The region will remain in the warm and
humid air on the south side of this boundary through the end of
the week with a daily threat of showers and thunderstorms.
Near term /through Monday/...
update as of 1150 PM EDT Sunday...
Line of showers and storms has quickly weakened upon approaching
southeast west VA so cancelling the going severe watch early.
With still some weak instability around would expect some
showers and isolated storms to continue over the west as some
redevelopment occurs upstream and off outflow. However not
expecting widespread or much in the way of strong storms so
running with low pops mainly mountains overnight. Otherwise few
added changes other than to add in more fog overnight.
Update as of 730 PM EDT Sunday...
Quick update for the issuance of Severe Thunderstorm Watch 389
across southeast west VA that will be in effect until 3 am. This
ahead of a complex of storms now in Kentucky that could continue to
organize and push east into the western mountains given
lingering instability. However lots of uncertainty to just how
far east these storms will make it given loss of heating with
some solutions weakening most of the storms to our west by
midnight. Otherwise updated to raise pops to low likelys and
intensity of storms in the watch area with only isolated coverage
farther east overnight where support is less. Temperatures
appear on track with lows in the muggy 60s overnight.
Previous discussion as of 225 PM EDT Sunday...
Moisture continues to increase in the low levels across our area, as
dewpoints have increased into the 60s. Residual outflow boundary
remains northwest of Greenbrier County this afternoon, and better
low level convergence remains north of the I-64 corridor. Visible
satellite plus web cams showing a capped atmosphere with limited
vertical development to the cumulus.
High-res models showing isolated coverage this afternoon mainly in
WV and downwind toward the I-81 corridor, but main development
upstream over Kentucky/Ohio appears to not reach our area this evening.
Westerly flow and ridge in the southeast will act to keep convection
limited in Southside Virginia and the NC Piedmont.
Convection will wane across the area late tonight, then appears an
earlier start to storms per synoptic models Monday, as better
surface convergence and just a drift southward in the upper waves
coincident with the front should bring storms further east and
south. The NAM and GFS are in agreement toward ramping up storms
along the Blue Ridge in the afternoon, with second area pushing into
WV during this time. Not everyone will see rain tomorrow, but
appears radar will be a lot more active. Severe threat will exist
though the shear is marginal to weak, but sbcapes reach 1500 to over
2000 j/kg, so some robust convection is not out of the question with
downbursts and marginally severe hail possible. Storm Prediction Center still has
marginal risk for much of the area Monday.
In addition, precip water values will be in the 1.6 to 1.8 inch
range, so torrential downpours are likely. Storm motion should be in
the 20 to 30 mph range, but further south the flow is weaker, so
will have to watch for training or some slower storms along the
southern Blue Ridge where have higher rainfall forecast. Localized
flash flooding in the mountains is possible.
For temps expect mild to muggy lows tonight in the 60s. Monday, high
temps will be dependent on how quickly we cloud up with
showers/storms and any upstream blowoff. Expect temps close to or
around 90 in the Piedmont where sunshine will be around longer, with
lower to mid 80s in the mountains.
Forecast confidence is medium on coverage of showers/storms this
evening and again Monday but higher on the rest of the weather
Short term /Monday night through Wednesday night/...
as of 330 PM EDT Sunday...
Warm and moist air mass remains in place through mid week, while
upper trough currently over the Southern Plains will be approaching
by late Monday night. However it will be be much weaker as it lifts
out in westerly flow by Monday night and into Tuesday. This could
help convection linger into Monday evening a little later than
otherwise simply due to diurnal cycle, and several models suggest
fairly strong convection firing over the Blue Ridge in the afternoon
will move into Piedmont and linger well into the evening. Increased
pops into mid chance range through about midnight for the time
being. Then for Tuesday with the aforementioned short wave moving
across this will provide a little extra lift, extra wind shear, and
at least some brief backing of low level winds to enhance upslope
convergence along Blue Ridge such that both a small risk of severe
storms as well as flash flooding are possible mainly along and east
of the Blue Ridge. Much depends on instability from degree of
daytime heating and while there could be some mid to high clouds
lingering for part of the day from upstream convection, believe this
will have minimal impact and with similarly warm/moist airmass
compared to Monday, believe the added upper wave and shear will help
some storms become strong. Storm Prediction Center marginal risk for the entire area
looks reasonable for now, but would not be surprised of the slight
risk area over northern Virginia for tues eventually gets expanded back
toward the southwest a bit.
Wednesday behind the short wave there is a bit more mid level dry
air which may entrain developing updrafts and help keep coverage
from being as high overall, but does not appear it will totally
suppress it, but overall moisture content is a bit less and storms
may not be quite as strong of have quite the same rainfall rates as
Wednesday. More of a westerly wind on back side of trough may also
prevent any convection from spreading too far east of Blue Ridge so
have somewhat higher pops in the west.
Long term /Thursday through Sunday/...
as of 355 PM EDT Sunday...
Warm and moist airmass remains in place with nearly stationary
frontal boundary just to our north most of the period, with a
stronger upper wave approaching on Thursday and moving east by
Friday. Still some discrepancy in timing so whether or not best
dynamics matches Thursday afternoon or not and how much mid-level
drying might take place by Friday afternoon still remains a
question, but for now have increased chances for showers and storms
for much of Thursday with likely pops for much of the area and could
once again have some chance for strong to severe and/or very heavy
localized rain. Also depicted drying trend by Friday and Friday
night even though we remain in the warm sector with no real surface
frontal passage but winds likely to turn more northwest and plenty of mid
level drying to take place so any shower or storm activity may be
confined to western slopes. Still some uncertainty as to timing of
this so if it slows down that could keep some precip chances a bit
higher until later in the day Friday.
The drying is short-lived however as upper ridge builds in again by
Saturday along with return of deeper moisture for the entire
weekend. Thus chances of showers/storms increase Saturday and more
so into Sunday. Near seasonal temperatures and increasing humidity
as well through next weekend. Generally pretty good agreement in the
guidance for these trends over next weekend.
Aviation /04z Monday through Friday/...
as of 705 PM EDT Sunday...
Mainly VFR continues through the evening with most convection
now all but faded and mainly to the south well away from the taf
locations. Cant totally rule out added isolated showers/storms
over the next couple of hours given outflow around but iffy.
Otherwise may see the next round of weakening showers arrive
from a complex well west of the mountains, with some this
coverage perhaps arriving toward midnight or later if it holds
Also the threat for fog increases overnight, espcly where
earlier downpours crossed over. This looks possible at kroa/kbcb
and klyh attm so added in a tempo group for MVFR vsbys in spots
before dawn on Monday. Also some fog possible around klwb, but
with clouds increasing ahead of next system, uncertainty to the
degree of fog coverage so leaving in high end MVFR there.
Monday morning will see VFR and increasing threat of storms
firing along the Blue Ridge and moving in from Kentucky/Ohio by early
afternoon. Since confidence in at least seeing decent coverage
along the Blue Ridge, added in some shower/thunder mention over
the west for now during late Monday afternoon.
Extended aviation discussion...
Active pattern Monday evening through Thursday with best chance
for storms each day, especially afternoon/evening as a wavy
front remains in place from the mid-MS valley to the mid-
Atlantic. Mainly VFR during the day aside from storms, with
potential IFR fog/low clouds late at night due to increased low
level moisture. Appears more in the way of VFR on Friday as
somewhat drier air arrives under weak high pressure.
Confidence is medium this time period.