National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 210000
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
800 PM EDT Sat Jul 20 2019

.SYNOPSIS...
High pressure will continue to build across the region into Sunday
resulting in a third day of the summer heat wave with
temperatures about 10 degrees above normal. A cold front should
cross the area later Monday bringing cooler and less humid
weather by the middle of next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 800 PM EDT Saturday...Heat indices have currently fallen
below heat advisory/excessive heat thresholds, but are expected
to reach those levels again tomorrow in the standing areas under
an advisory/excessive heat warning. To clear up any confusion
(e.g. why a heat product is in effect when heat indices are at
their lowest point in the diurnal cycle), I tweaked some of the
phrasing in the NPW text product for the heat advisory/excessive
heat warning. The text changes are somewhat nuanced, but tries
to convey that the highest heat indices will be for Sunday
afternoon with little relief expected tonight. Hopefully, that
helps to clarify things.

Still a very warm and muggy early evening across the area, with
current temperatures having cooled into the mid-upper 80s. Did
add some isolated thunderstorms across Monroe, Summers and
southern Greenbrier County through late evening based on current
radar trends. These will likely be short-lived and unlikely to
reach even strong levels as daytime instability wanes with loss
of strong insolational heating. Strongest convective activity
currently is over southeast KY and northeast TN, buoyed by weak
vorticity maxima in southeast low/mid-level flow which is
helping to induce a weakness in the heat ridge. 18Z GFS brings
some of these showers or storms into Tazewell and Smyth counties
after midnight - confidence is pretty low if this does occur
given lack of other guidance agreement. Will continue to monitor
and if trends and/or forthcoming guidance indicate better
chances, I`d then look to increase PoPs in this area but too
uncertain to go any higher than 20% PoPs.

Previous discussion from 250 PM Saturday...

Dangerous heat wave ongoing from the central CONUS to the East
Coast.

Excessive Heat Warnings and Heat Advisories extend from parts of the
Kansas to the Middle Mississippi/Ohio Valleys and parts of the Great
Lakes as well as parts of the Northeast southward to the Southern
Mid-Atlantic as upper-level ridging extends from parts of the
Southwest eastward to the Northeast/Mid-Atlantic. Hot air is being
funneled from the desert Southwest all the way across the country,
and combining with high levels of moisture off both the Gulf of
Mexico and western Atlantic (dewpoints in the mid-upper 70s) to
produce high heat indices. Afternoon temperatures in the mid to
upper 90s combined with high dewpoints will result in heat indices
of between 105 to 115 for a big chunk of the country.

Temperatures across the foothills and piedmont have warmed into the
mid to upper 90s with heat indices into the triple digits this
afternoon. With less of a chance for a cooling shower or
thunderstorm across the piedmont tomorrow, a repeat of Heat
Advisories and Warning criteria are again expected during the
afternoon. Mountain temperatures have also been very warm today with
readings in the upper 80s to lower 90s. Temperatures may be a little
cooler across the mountains Sunday with a better chance for
afternoon and evening showers. Temperatures will still remain warmer
than normal with highs in the mid to upper 80s.

For most of the day today, showers and thunderstorms have been
confided to a boundary draped along a line from Raleigh to Boone NC.
This convection may wobble slightly to the north and south before
fade this evening. Once west wind mixing decreases this evening,
scattered showers and thunderstorms may form and linger into the
early morning hours across the area.

The upper level ridge will slowly move east and weakening on Sunday
well ahead of height falls aloft in advance of a developing upstream
trough. The moisture and energy aloft associated with an upper wave
along the Gulf coast will try to lift northeast and split the heat
dome in two. This may be enough to create some scattered showers and
thunderstorms along and west of the Blue Ridge given the flow
turning more southwest ahead of the cold front to the northwest.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 230 PM EDT Saturday...

Diurnal convection likely to linger at least over the mountains
Sunday evening with perhaps some of this coverage persisting
across the north into the overnight as a weak wave aloft unfolds
to the northeast. However with loss of heating not expecting
much more than chance coverage despite progged lingering
instability through the night. Otherwise partly to mostly cloudy
and muggy with only isolated pops over the southeast in the
evening and then dry overnight outside of the northwest. Lows
mainly in the 70s with a few 60s mountains.

Pattern change will take shape heading into early next week as a
sharp mid level trough dips southeast toward the area Monday
before passing overhead Tuesday/Tuesday night. Models suggest
either a lead pre- frontal trough or residual outflow will enter
the region Monday afternoon ahead of the actual surface cold
front that wont push through until Monday night or early
Tuesday. Decent instability given lingering moist dewpoints and
increasing southwest flow aloft ahead of the upstream shortwave
trough should act to generate clusters/bands of convection over
the higher terrain Monday afternoon before progressing into the
eastern lee trough later in the day. Since still appears a bit
slower, cut back on pops early Monday followed by likelys to low
end categorical across the west Monday afternoon and high
chances out east. With forecast soundings showing an inverted V
under dry air aloft appears some pulse severe potential into
late Monday. Highs still quite warm outside of the far west with
readings likely topping back into the low/mid 90s east, and
low/mid 80s for most of the mountains, but below heat advisory
headlines at this point in the piedmont.

Surface front pushing into eastern sections by early Tuesday will
be followed by the 850 mb boundary along the leading edge of
the trough aloft into Tuesday afternoon. Still some uncertainty
as to how things may evolve between features as guidance shows
added showers over the west with the dewpoint type boundary
later Monday night and then enhancing these showers upon heading
southeast during the day under cooling aloft. This may be more
post frontal nature type rainfall with limited thunder except
over the southeast in the afternoon per instability. However
given consensus of solutions indicating a decent band of lift
and subsequent rainfall, went ahead with higher pops Tuesday
that should decrease from northwest to southeast by late in the
day. Will be cooler with lows mostly 60s Monday night and only
in the 70s to low 80s Tuesday under the clouds and influx of
cool advection.

Axis of deep moisture will finally slide to the southeast Tuesday
evening resulting in clearing skies and lower dewpoints. May see a
few showers linger southeast into the evening espcly if a wave
forms along the boundary, otherwise decreasing pops/clouds with
skies clearing from northwest to southeast by morning. Will be
much more comfortable with lows in the 50s and 60s with even a
few upper 40s in the valleys.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 100 PM EDT Saturday...

Mean upper trough regime will dominate starting midweek with a brief
return to more zonal flow by the weekend. This combined with cooler
surface high pressure building into and northeast of the region should
lead to mainly dry as well as much more comfortable conditions through
much of the period. However moisture may slowly return into far
southwest sections by late in the week and across the mountains next
Saturday. Thus will include some isolated pops along portions of the
southwest mountains given heating/orographics but iffy since still
looks quite dry aloft. Otherwise plan to leave out pops with mainly
sunny days and clear overnights for most of the area at least into late
week. Highs mostly 70s mountains to low/mid 80s east given rather cool
850 mb temps for late July except a bit warmer by Day7 as weak return
flow develops. Lows quite pleasant with 50s west, including perhaps a
few 40s valleys Thursday/Friday pending fog, and mostly 60s east of the
Blue Ridge.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
As of 800 PM EDT Saturday...

VFR conditions should predominate until overnight when we`ll see
opportunity for sub-VFR mist/fog in the western mountains
(mainly affecting Lewisburg and Blacksburg). Didn`t hit visbys
as hard with afternoon temperature-dewpoint spreads being
rather sizable. Kept visbys no worse than prevailing MVFR, with
a tempo IFR at Lewisburg. Winds light southwesterly.

Any mist/light fog should erode quickly with heating by early
Sunday morning. Will likely see greater thunderstorm coverage by
as soon as early afternoon, but overall coverage likely no
better than scattered and mainly in the mountains. Will indicate
VCSH after 17z at Roanoke, Lynchburg, Bluefield and Blacksburg.
Winds mainly light southwest under 6 kts.

.Extended Aviation Discussion...

Sunday afternoon, a bit better coverage of showers/storms is
expected late Sunday and even better chances Monday as a cold
front approaches slowly from the west. The front is expected to
stall in or near the area thereafter leaving good chances for
showers and storms just about every day next week, especially
along and east of the Blue Ridge. Temperatures will be cooler,
however.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Heat Advisory until 11 PM EDT Sunday for VAZ034-035-044-045.
     Excessive Heat Warning until 11 PM EDT Sunday for VAZ046-047-
     058-059.
NC...Heat Advisory until 11 PM EDT Sunday for NCZ005-006.
WV...None.

&&

$$
SYNOPSIS...RCS
NEAR TERM...AL/RCS
SHORT TERM...JH
LONG TERM...JH
AVIATION...AL/RCS