Scientific Forecaster Discussion
fxus62 kgsp 230225
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1025 PM EDT Thu Jun 22 2017
the remnants of Cindy will move northeast into southern Arkansas
tonight while widespread tropical showers impact our region through
Friday morning. Shower coverage decreases briefly Friday morning
before a cold front approaches the mountains later in the day.
Showers and storms return Friday afternoon and evening as the cold
front slides into the region. Light showers linger on Saturday as
the front slowly departs the area, but unseasonably cool and dry
weather follows the front and will persist through next Thursday.
Near term /through Friday/...
as of 1025 PM edt: widespread showers have spread across the area. A
line of thunderstorms are moving out of NE Georgia and into the western
upstate. With lingering instability and good shear in place, a few
of these storms could produce damaging winds or even a tornado. The
threat of severe will diminish as the line moves into the eastern
upstate. Instability is much less over that area even though good
shear could continue. Instability is also much less across NC. An
isolated storm cannot be ruled out, but the chance of severe storms
is low. Cannot rule out any Hydro issues, but they should be limited
by the relative fast movement of the cells. The precipitation should
exit to the northeast overnight.
Otherwise, transient upper divergence will move up the NC mountains
through the near-term, but the 500 mb ridge over the southeast will
become resurgent to promote subsidence later tonight through Friday.
Drier air will wrap into the region under the building ridge, with
deeper tropical moisture shunted northwest toward the Tennessee border.
Meanwhile, the remnant Cindy circulation will move up the
Mississippi River valley through tonight and then east through
Kentucky on Friday, but with the deepest moisture west of the
mountain chain through late day. 850 to 500 mb lapse rates should
briefly build to 6+ deg c/km over the western mountains to support
scattered thunder chances there Friday afternoon. Sbcapes are
highest in southeast Piedmont sections Friday afternoon, but with no
triggering and more capping evident there. Expect more robust SW
winds and gusts with mixing on Friday afternoon.
Short term /Friday night through Sunday/...
as of 100 PM EDT thursday: at the start of the period, robust and
perhaps organized thunderstorms may be ongoing west of the mountains
within the encroaching llvl baroclinic zone and deeper layered
shear. The eastward translation of this feature should be able to
maintain numerous to widespread cvrg of deeper convection into the
NC/Georgia mountains Friday evening before diminishing east of the Blue
Ridge overnight within the waning instability.
Aforementioned frontal zone remains progged to sag southeast through the
cwfa on Saturday. Slow moving front should be able reactivate in the
afternoon, and current timing would suggest the potential for a few
strong storms in the Piedmont. The leading edge of a Continental
airmass featuring a progrssive lowering of sfc dwpts is expected for
Saturday night. This front is then progged to stall along the
coastal plain on Sunday and it is shaping up that any additional
showers will be limited to the I-95 corridor to the coast.
Atop the western Carolinas on Sunday though, developing sunshine is
expected with Max temperatures about a category below climo and sfc
dwpts toppping out a rather comfortable level.
Long term /Sunday night through Thursday/...
the sensible weather for the extended period will be about
as good as it's going to get for late June, with temperatures
running 5 to 10 degrees below normal and very pleasant humidity
values courtesy of dewpoints from the lower 50s to the lower 60s.
Aloft, the region begins the extended with a broad but fairly
deamplified longwave trough centered over the Great Lakes/Ohio
Valley/Tennessee Valley. A reinforcing shortwave trough digs south across
the Great Lakes Monday into early Tuesday, amplifying the longwave
trough and pushing its axis east past our region late Tuesday into
early Wednesday. With the longwave trough slow to propagate east
and surface high pressure centered across the mid-south, weak Lee
troughing will set up east of the Blue Ridge for Monday until a
reinforcing Continental high pressure system underneath height rises
behind the shortwave Ushers in an even cooler and drier airmass
for mid-week. As a result of the modified airmass overhead for
Monday, a lingering slight chance for isolated showers exists until
early Tuesday when dry weather dominates through at least Thursday.
Model discrepancies return to the forecast towards the end of
the period early Friday when there is some potential for another
shortwave trough to eject out of the upper Midwest and breakdown the
subtropical ridge across the southeast. The GFS is most bullish
about the ridge dominating our pattern, keeping US dry into the
weekend, while the ec and Canadian center the surface ridge offshore
in advance of an upstream cold front and bring a chance for showers
back to the forecast within modest Gomex return flow. For now the
forecast is a blend largely to stay in agreement with the neighbors.
Aviation /03z Friday through Tuesday/...
at kclt: widespread showers have moved east. However, showers will
return later this evening with MVFR restrictions. Cannot rule out a
tsra, but confidence not high enough for now. MVFR lingers through
the overnight after the showers move east. Skies lift to low VFR by
mid morning then scatter out for the afternoon. Light southeast wind
becomes S overnight. Winds increase in speed from the south-southwest during the
morning with gusts for the afternoon. Precip chance too low to
mention for the afternoon.
Elsewhere: instability has developed over the SC sites. Thunderstorms and rain will
cross the area this evening with MVFR restrictions. Kavl/khky will
only see showers but will also see MVFR restrictions. MVFR continues
through the night after the showers move east. IFR cigs cannot be
ruled out. Skies lift and scatter out through the morning. Kavl has
the best chance for afternoon convection, so prob30 was added there.
Light southeast wind this evening becomes S overnight then increases in
speed from the SW during the morning with gusts for the afternoon.
Outlook: abundant moisture will return from the west with the Cindy
remnants Friday night into Saturday. Anticipate fropa and drying
Sunday to usher in a period of drier weather through the middle of
02-08z 08-14z 14-20z 20-00z
kclt high 88% high 88% high 91% high 100%
kgsp high 86% high 93% high 100% high 100%
kavl high 94% Med 72% high 100% high 100%
khky high 86% high 81% high 97% high 100%
kgmu high 86% high 93% high 100% high 100%
kand Med 71% Med 78% high 96% 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: