Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS62 KGSP 260719

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
319 AM EDT Mon Jun 26 2017

Dry and cool air will continue to spread in from the northwest over
the forecast area through much of the week as Canadian high pressure
remains to our north. An upper level disturbance will bring a chance
of rain to the area on Tuesday, and then as the high moves offshore
late this week, moist southerly flow will return, along with a
chance of mainly afternoon thunderstorms.


As of 310 AM EDT Monday: we have mostly clear skies overhead with
just a few high clouds streaming overhead and some lingering stratus
moving over the far SE zones from the SW as a weak frontal bndy
remains to our SE. The stratus should gradually dissipate to our SE
later this morning as the deeper moisture gets pushed offshore.

Otherwise, broad upper trofing will remain over the eastern CONUS
with steep upper ridging persisting over the west. As we move into
Tuesday, a shortwave will round the backside of the upper trof and
approach the CWFA from the NW by the end of the period at 12z. This
will generate some mid to upper lvl divergence over the higher
terrain, thereby promoting ascent over the area. I kept a slight
chance PoP over the higher terrain to reflect this, otherwise the
period will be dry. At the sfc, cooler and drier Canadian high
pressure will remain over the region thru the period. A weak,
reinforcing cold front will move through the fcst area later this
morning and bring slightly cooler and drier air to the region. In
its wake, the models still show some sort of weak lee trof briefly
setting up later this afternoon and lingering into tonight. Whether
or not this actually materializes remains to be seen. Temps will be
about a category below climatology thru the period.


As of 230 AM EDT Monday: As the short term begins, a sharp upper
trough will be pushing toward the Appalachians, with increasing PVA
and a strong upper jet lifting to the NE, leaving us in the right
entrance region of the jet streak. Moisture associated with this
upper wave will push into the mountains just before the start of the
period, and should be enough for at least a chance of showers
through the afternoon. Cannot rule out a few rumbles of thunder, but
not really enough CAPE to work with for much in the way of
instability. Increasing cloud cover plus decreasing thicknesses
aloft will lead to temperatures 7-10 degrees below seasonal normals
(upper 70s to lower 80s across the Piedmont). This wave, and
associated reinforcing surface cold front, will push through Tuesday
night with another drop in temperatures expected for Wednesday
morning lows, a good 10 degrees below normal. A return to full sun
on Wednesday will compete with the weakening CAA behind the front,
with only a slight recovery for afternoon  highs. Flow aloft
flattens late Wednesday into Wednesday night as the surface high
moves offshore, bringing return flow into the area by the end of the
period, with lows still below normal but on a bit of an increasing
trend. Over all, with the exception of some Tuesday afternoon
showers, a really really nice period.


As of 245 AM EDT Monday: With the extended portion of the forecast
comes a bit of a pattern change from the cool/dry conditions to
average (temps)/wetter conditions. Near zonal flow aloft over the
northern half of the country will allow a sharp shortwave crossing
the northern tier into the Great Lakes to push east, dragging a
front across the Mississippi and Ohio Valleys. The surface high
pressure that brought us the pleasant temps in the short term will
continue to hang around off the Eastern Seaboard, with return flow
lifting Gulf moisture into the Deep South. By Thursday afternoon,
lightly-below-diurnal pops should return to the mountains as
temperatures creep ever so slightly back toward seasonal normals
(but still 3-5 degrees below).

A stronger wave dives out of the Canadian Rockies toward the Upper
Midwest Thursday night into Friday. Stretching off the Rockies as
the trough pushes into the Plains will result in a big of a wiggle
in the flow, and with continued moist return flow at the surface,
should see a real enhancement to pops by Friday afternoon as the
wiggle turns into a true shortwave over the Midwest. The associated
front takes on slightly better shape by Saturday, with flow aloft
transitioning to more SW, and widespread moisture warranting
widespread chance pops to some likelies over the mountains. By this
time, highs will be just a couple of degrees below seasonal normals
(tempered by cloud cover), with lows now above average due to the
increasing surface moisture. Actually kind of uncomfortably muggy by
this point, but at least not ridiculously hot. With the front
nearby, there might be some concern about more significant
convective activity, but for now doesn`t look like much more than
what we would expect with pulse severe...just perhaps slightly more
widespread. The Canadian Rockies trough pushes east into eastern
Ontario/western Quebec by the end of the period, though the trough
axis for now does not look like it will have crossed the
Appalachians, so an enhanced diurnal trend to pops continues for the
end of the week as an upper ridge begins building into the Southern


At KCLT and elsewhere: expect VFR conditions to persist over the
fcst area thru the taf period. A persistent area of enhanced upper-
level divergence to our north will continue to bring a few high
clouds over the region thru the overnight and into the morning. In
addition, some sct stratus in the 4 to 6kft range continues to
stream across our southern zones as deeper lyr moisture and a weak
frontal bndy linger to our southeast. Most of this cloud cover
should dissipate over the next 4 to 6 hrs as the deeper moisture
gets pushed farther south. Winds will remain light and NLY through
most of the period. More of the guidance is now backing winds to
more of a WLY direction by the late afternoon at all sites except
KAVL in response to a weak lee trof developing briefly. I included
this wind shift in the TAFs, however confidence is not very high.

Outlook: Light winds and VFR conditions should continue through mid
week. Moist, SLY return flow will return around the offshore ridge
by Thursday.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     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:




AVIATION...JPT is the U.S. government's official web portal to all federal, state and local government web resources and services.