Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 211937
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
237 PM EST Tue Feb 21 2017
A frontal boundary will push across the area tonight and Wednesday,
bringing a good chance for some modest rainfall. This will be
followed by brief drying, before another frontal system brings
additional chances for rain and thunderstorms late Friday or
Saturday. Overall, daytime temperatures will remain well above
normal through the weekend.
.NEAR TERM /THROUGH WEDNESDAY/...
As of 200 PM EST...An upper low will drift from the ARKLAMISS to
near Tampa, FL by the end of the day on Wednesday. This will place
our area under a col in the upper flow with the northern jet stream
staying well to the north over the Great Lakes. In the low levels,
south/southeasterly flow will continue to gradually advect more
moisture into the area. Upslope lift along the south and east-facing
escarpment should begin to produce increasing showers this evening
thru the overnight. Overall forcing will remain weak, and guidance
in good agreement on low QPF in this flow regime. The moisture will
produce widespread stratus tonight, which will keep temps elevated
well above normal with lows in the upper 40s to mid-50s.
On Wednesday, the upslope flow and deep moisture should keep at
least isolated to scattered light showers along the escarpment thru
most of the day, while the rest of the area should remain fairly
socked in with low clouds. A 1028 mb surface high will drift off the
Mid-Atlantic coast and weaken. So it`s tough to say how much of an
in-situ wedge may linger across the Piedmont thru the afternoon. In
any case, the clouds should keep a lid on temps, and highs are
expected to "only" warm into the low to mid-60s across most of the
area. If the low clouds manage to erode along the south and east
fringe of the CWFA, temps may get into the low 70s per the MET MOS.
This may also unveil a little sbCAPE in the southern Upstate. Lapse
rates look rather weak in the soundings, so only a slight chance of
thunder will carried in the southern fringe.
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 215 PM EST Tuesday: The closed upper level low pressure system
near the west coast of FL crosses the FL peninsula through Thursday.
North of this system, H85 southerly flow will continue but slowly
weaken through this time. With copious low level moisture in place,
the upglide and upslope flow will lead to isolated to scattered
showers across the area Wednesday night and Thursday. Weak
instability will lead to isolated TSRA Thursday afternoon. With the
low level inversion eroding and the less widespread and showery
nature of the precipitation, highs and lows will increase to 15 to
20 degrees above normal.
Mid and upper southwesterly flow develops on Friday between the
weakening upper low off the SE Atlantic coast and a deepening upper
low and trough over the upper Midwest. The weak surface ridge over
our area erodes as a cold front moves into the MS valley. Southerly
H85 flow lingers through the period along with low level moisture.
Expect isolated to scattered convection to develop across the
mountains and foothills of the Carolinas and NE GA. Highs and lows
will remain nearly steady from 15 to 20 degrees above normal.
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
of 220 PM Tuesday: A strong, but weakening short wave trough will
lift from the Miss Valley through the Ohio Valley/Mid-Atlantic and
off the Northeast Coast early in the medium range period. This will
give way to the return of a progressive/quasi-zonal regime early
next week, before the flow begins to amplify again late in the
period as the next western storm system approaches the Rockies.
Early in the period, a cold front associated with aforementioned
strong short wave will sweep across the TN Valley. However with much
of the deep-layer forcing expected to lift west and north of the
southern Appalachians, an expected weakening frontal circulation,
and the likelihood that the meager pre-frontal surface-based
instability will deplete further as it approaches western NC, it
continues to appear as if any convective band accompanying the front
will lose considerable steam as it moves into the forecast area late
Fri night/early Saturday, with the bulk of significant shower
activity likely passing north of the area. Pops during this time
will range from likely across the western-most NC mtns, to only a
low chance across much of the Piedmont.
Conditions will dry out considerably behind the front on Saturday,
although max temps will once again range from 10-20 degrees above
climo. A brief period of NW flow rain and snow showers will be
possible Sat night, but chances will be slight at best.
The remainder of the period will be generally dry and unseasonably
warm (although 5-10 degrees cooler than what has been seen for much
of this week.) A couple of short wave troughs may pass near the
region early next week, but their potency will be weak in the fast
zonal flow, so any chances for showers will be low. More substantial
chances for precipitation will likely hold off until after the end
of this forecast period.
.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
At KCLT...the low levels will gradually moisten this evening thru
the overnight, as persistent southerly flow advects gulf moisture
into the area. I expect low VFR cigs to develop in the 22-24z time
frame, then cigs lowering to MVFR, then IFR overnight. Best chance
for showers will be in the 10-14z time frame, so will go with
prevailing SHRA. Precip rates should generally be light. A lingering
wedge may bring the winds around from SE to NE when the most
widespread precip moves thru, but then there`s high uncertainty on
whether they will turn back to SE around miday Wednesday. The
lingering wedge will keep low CIGS well into the day.
Elsewhere...As with CLT above, expect gradual deteriorating
conditions with MVFR cigs spreading across the area from late
afternoon thru the evening, then lowering to IFR at all sites
overnight. Showers should move in overnight, but will be generally
light. Still expect some VSBY restrictions in the precip with some
BR. Conditions will be slow to improve on Wednesday as a wedge
lingers across the area. This will bring winds around from SE to NE
across the Piedmont.
Outlook: Moist southerly to easterly low-level flow will persist
across the area until a cold front pushes thru on Saturday. This
will keep high chances of morning stratus and possibly fog each day
thru Saturday morning.
19-01Z 01-07Z 07-13Z 13-18Z
KCLT High 100% High 93% Med 70% High 81%
KGSP High 100% Med 78% Med 67% Med 73%
KAVL High 100% High 85% High 87% High 91%
KHKY High 100% High 96% Med 76% High 81%
KGMU High 100% Med 79% Med 73% Med 76%
KAND High 100% Med 64% Low 48% Med 74%
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: