Scientific Forecaster Discussion
fxus62 kgsp 221913
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
313 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 240 PM edt: mainly light rain continues to stream across the
forecast area from the southwest this afternoon, but regional radars
show a current lull in upstream activity over northern and central
Georgia. Additional convection in the outer tropical bands of the
Cindy remnants continue to develop over Alabama, and recent hrrr
runs suggest that some of this activity could survive and make a
northeast run across our forecast area later this evening. Rainfall
rates have been meager enough so far that any brief evening tropical
convection should not cause any significant Hydro issues. There will
also be an uptick in shear through late evening as the 850 mb jet
strengthens to 30 or 35 kt and backs slightly, but instability has
been paltry thus far and should remain so ahead of the convection.
Any passing precipitation should exit to the northeast shortly after
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 /19z Thursday through Tuesday/...
at kclt: widespread light rain continues around the terminal area,
but with all VFR ceilings associated with the precipitation. The
last round of any nearby scattered showers this evening should move
north of the area, with any precip threat ending. However, lower
ceilings will start to develop in the moist boundary layer, with
lowering MVFR clouds likely and IFR quite possible by daybreak.
Anticipate steady improvement to VFR through Friday morning as drier
air wraps in aloft. Gusty winds will develop from the southwest with
mixing on Friday, and precipitation chances are too small to mention.
Elsewhere: rain and embedded showers continue to cross the terminal
forecast area from the southwest late this afternoon, and one
additional round of showers with isolated thunderstorms will be
possible this evening as tropical moisture arrives from Alabama.
Anticipate a downward trend through MVFR ceilings with a period of
IFR developing in the pre-dawn hours as conditions dry out aloft.
Expect southwest winds to strengthen on Friday with gusts developing
by late morning. Precipitation chances are too small to mention for
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
19-01z 01-07z 07-13z 13-18z
kclt high 100% high 100% Med 77% high 94%
kgsp high 100% high 80% Med 74% high 93%
kavl high 87% high 87% Med 68% high 89%
khky high 100% high 94% Med 74% high 82%
kgmu high 100% high 80% Med 75% high 93%
kand high 92% high 86% Med 76% high 93%
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: