Scientific Forecaster Discussion
fxus62 kgsp 211406
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1006 am EDT Wed Aug 21 2019
expect a return to more typical late Summer heat and humidity today
through Friday as a cold front slowly approaches the area from the
northwest. The front will push into the region late Friday through
Saturday, then gradually settle just to our south Sunday into early
next week. An area of high pressure will build in from the north and
maintain cooler than normal temperatures and lingering moisture
behind the front.
Near term /through tonight/...
as of 1000 am EDT wednesday: minor adjustments made to
temperatures/sky/pop to coincide with latest trends, as the rest of
the near term forecast remains on track. Aside from a few light
showers along the Tennessee border, conditions remain dry across the area
this morning, with clouds continuing to burn off across the upstate
and northwest Piedmont. Otherwise, it's humid, with dewpoints in the lower
70s, and current temperatures in the mid to upper 70s/lower 80s.
Previous discussion: as a ridge continues to build over the Southern
Plains, a weak 500 mb vort lobe will cross the area during the peak
heating hours. The energy may help trigger convection in the usual
high terrain points by early aftn. Low to mid-lvl flow will shift
from southwesterly to wnwly, steering convection toward the Piedmont late
aftn into early evening. Also, a weak Lee trough will set up and may
enhance some convergence along the I-85 corridor. With all that
said, guidance is showing just modest SBCAPE and dcape potential. It
looks like severe threat from these storms will be slightly higher
than yesterday, but not as high as Monday. With some mid-lvl dry
air, pwats come down a bit (mainly 1.5-1.9"). The morning will start
out with areas of fog and stratus, but should mix out to partly
cloudy skies. So a rebound in temps back into the upper 80s to lower
90s is expected east of the mountains.
Tonight...a northern stream trough will begin to dig across the
upper Midwest, allowing a cold front to push into the Ohio Valley.
Convection is expected to be ongoing across the Ohio Valley thru the
evening hours, but should weaken/fizzle out as it approaches the
southern Appalachians. There will be enough elevated cape and a
light west-northwest flow that could trigger a few showers along the Tennessee border
due to some upslope forcing. The rest of the area should be dry
overnight with patchy fog and stratus developing once again. Lows
will be a category or two above normal.
Short term /Thursday through Friday night/...
as of 315 am EDT wednesday: heights will fall sharply across the
Great Lakes on Thursday, but the associated northern Continental U.S. Surface
cold front will make only limited progress southward toward our
forecast area. In the moist and unstable airmass along and near the
southern Appalachians well south of the boundary, afternoon
convective triggering is once again likely along the Blue Ridge
Mountain Escarpment early Thursday afternoon. This activity should
run east across the Piedmont in the westerly steering flow through
late day to warrant solid likely pops west to solid chance east.
Temperatures will remain above climo.
Moisture will deepen as the frontal boundary slowly settles
southward toward the forecast area on Friday. The front may stay
just north of western NC through late day, permitting an unstable
warm sector to stay in place most of the day. With SBCAPE values
running 2500 j/kg and precipitable water values closing in on two
inches, can probably introduce some heavy rain wording into the severe weather potential statement.
Long term /Saturday through Tuesday/...
as of 320 am EDT wednesday: a surface cold front is expected to
settle southward through the forecast area on Saturday. Upper-level
confluence over the northeast will aid cold air damming development
east of the Appalachians over the weekend, especially with another
round of height falls developing from the mid-MS river toward the
Appalachians. This will enhance upglide to help establish the cad
layer on Saturday and then maintain it Sunday, and beyond, as The
Wedge front settles south of the area. Anticipate The Heart of the
cold air damming conditions to be in place on Sunday, with maximum
temperatures struggling in the 70s east of the mountains. A heavy
rainfall threat could well remain in place as high precipitable
water air persists in profiles, but instability and associated
precipitation rates will be more of a question mark. Will hold off
on any weekend additions to the severe weather potential statement.
The upstream trough will cross the southeast early next week to
finally provide some measure of erosion of the surface wedge layer,
with gradual shallowing on Monday and then scouring on Tuesday. Will
keep well above climo pops going and permit temperatures to slowly
rebound to a little closer to normal by Tuesday afternoon.
Aviation /14z Wednesday through Sunday/...
at kclt and elsewhere: a weak mid-lvl low continues to slowly drift
northeastward thru the area, producing slow-moving shwrs and tstms that are
shifting east of clt. The rest of the taf sites are expected to be
dry overnight. With all the rain that fell yesterday, and a light
warm air advection southwesterly flow in the low-levels, there should be areas of stratus
developing across much of the Piedmont and valley fog/stratus in the
mountain valleys. Most of the stratus looks to be over the NC
foothills and Piedmont, affecting khky and kclt. The upstate sites
are less certain, and will be depicted by tempos for now. Conditions
should improve fairly quickly after daybreak today, as flow turns
out of the west/northwest and scours out some of the moisture. Convection is
expected to develop with peak heating across the high terrain first,
then generally expand/drift east into the Piedmont late aftn into
the evening. All sites will carry prob30 for thunderstorms and rain. Winds will be
light out of the S/SW overnight, increasing slightly out of the SW
Outlook: rain showers/thunderstorms and rain chances will increase with a cold front
Thursday and Friday, remaining elevated thru the weekend as the
front stalls over the area. Some morning fog and low stratus will be
possible each day, especially in the mountain valleys.
14-20z 20-02z 02-08z 08-12z
kclt high 93% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 100% high 100% Med 71%
khky high 100% high 100% high 100% high 100%
kgmu high 98% high 100% high 100% high 100%
kand high 100% high 100% high 100% high 100%
The percentage reflects the number of guidance members agreeing
with the scheduled taf issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link: