Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 220608
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
108 AM EST Wed Feb 22 2017
A weak frontal boundary passes east of our area today.
This will be followed by brief drying on Thursday before a more
significant cold front 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 TODAY/...
100 AM EST Update...Made some minor tweaks to hr/ly temps and
td/s...but the atmos has become rather steady state with a moist
locked in wedge. Light precip is panning out generally as planned
and expect areas north of I-85 and the far wrn zones to have the
best chances thru the morning fcst package.
As of 1010 PM EST Tuesday: Little change across the region since
the last update. However, its seems the PBL is moistening as a
few observations across the region are indicative of precipitation
making it to the ground amidst pockets of upglide induced dz/ra.
Thus, will opt for no changes to pops with this update. Did tweak
t/td through the overnight as latest cons guidance favors slightly
warmer min temps given ovc skies. That said, still expecting some
evaporative cooling effects, therefore didn`t feel comfortable
raising mins much further than a degree. Otherwise, no sig changes
needed/made with this update.
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 /TONIGHT 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 /06Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and Elsewhere: Light rain showers are beginning to increase
in coverage along and north of the I-85 corridor. Most locales are
currently running MVFR CIGS...except VFR at KHKY and KCLT. With
continued moist flux atop a weak wedge...expect all sites to dip
into the IFR range due to CIGS around or aft 09z. Have included
TEMPO IFR for this possibility btw 09z-12z. Not too concerned with
dense FG as -shra is weak and cloud cover thick...but MVFR BR is
likely across most sites...perhaps TEMPO IFR esp at KAVL. With no
FROPA today...the atmos will remain weakly forced and moist within
the sfc layer...thus will keep IFR conds thru 18z or so. A general
improvement to MFVR/VFR this afternoon / evening is probable...then
back to IFR conds most locales overnight as wedge persists coupled
with moist llvl se/ly flow.
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.
06-12Z 12-18Z 18-24Z 00-06Z
KCLT High 80% High 84% High 82% High 90%
KGSP High 92% High 81% High 85% Med 73%
KAVL Med 67% Med 61% High 85% Med 73%
KHKY High 83% Med 60% Low 51% High 80%
KGMU High 91% Med 77% High 83% Med 78%
KAND High 88% Med 71% High 85% Med 78%
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: