Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 290731
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
331 AM EDT Sat Apr 29 2017

.SYNOPSIS...
A Bermuda high will continue summer like weather across the western
Carolinas and northeast Georgia through the remainder of the weekend
until a strong cold front approaches from the west Sunday night. The
cold front will move across our region on Monday. After the front
passes, weak high pressure will move across the southeast for
Tuesday and Wednesday. However, the atmosphere will reload with
another slow moving system bringing wet weather to the area late next
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM EDT: Bermuda high pressure will remain dominant over
the southeastern U.S. today through tonight. Cirrus slipping over
the area under the ridge early this morning will help to keep
morning fog and low clouds less prevalent than yesterday, but patchy
fog is still likely around daybreak. Otherwise, expect continued S
to SW low level flow to keep dewpoints up in the 60s and boundary
layer moisture relatively high. Temperatures will likely max out in
the upper 80s in many locations, with mid 80s in the lower mountain
valleys. Little to no upper forcing is apparent today, but weak
upslope triggering will be possible near the southern mountains,
with some low-level convergence expected as well in the upper
Savannah River valley. Isolated to scattered coverage is showing up
in the numerical models/CAMs this afternoon and that could prove
troublesome given the model indicated instability. Although there
will be abundant CINH to be overcome at low levels this morning,
model profiles suggest that this is indeed overcome after 18Z and
then tremendous CAPE values of 4000+ J/kg could be realized with any
deep convection that manages to form. All told, this means limited
thunderstorm coverage (best in southwest sections) but with a
reasonably good chance of severe weather with any convection that
does manage to form. Large hail will be quite possible and delta
theta e values of 30 to 35 K suggest a microburst wind threat as
well. Will include an HWO mention for this.

Isolated shower triggering could continue in upslope areas tonight,
but with profiles quickly stabilizing with the loss of diurnal
heating. Another mild night is expected, with fog and low stratus
possible depending on the thickness of any invading cirrus.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 245 AM EDT Saturday: Strong sub-trop high pressure will remain
the dominant synoptic feature Sun. The models are in decent
agreement with the amount and location of llvl moist flux...which
shud be enuf to create stcu persisting thru the morning and early
afternoon most locales. The main challenge Sun will be when and if a
strong subs inversion is overcome by thermal heating. Mech lift will
aide in sct tstm development across the higher terrain...but it
looks like spotty and later day precip/thunder non/mtns. Not
expecting much severe potential as muCAPE is rather low and tapped
into rather late day. There is a nice vertical delta theta/e sig
showing up in the cross sections...but then again mixing shud remain
too shallow to tap into it. Tricky max temps if the llvl stcu
remains trapped...but for now have values cooler than the
expected highs today...basically L80s non/mtns and U70s mtn
valleys.

The main event for the short term will be the incoming cold front
and highly dynamic upper support thru the day Mon. Pre-frontal
forcing will begin Sun night and an increase in showery activity is
anticipated across the mtns. Model soundings are rather impressive
with the strengthening shear. By 15z...a 50+ kt llvl jet will develop
ahead of the front. Instability is a little suspect...but higher
than the past few runs. High effective shear shud combine with
muCAPE values around 1500 J/kg by the afternoon and will expect
organized multi-cell tstms to be maintained as the front crosses
east of the FA by 00z or so. A decent airmass mix behind the front
and sfc td/s drop into 40s Mon night. With opaque cloud cover most
of the day...max temps shud only reach arnd normal even with sustained
sw/ly flow.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 315 AM EDT Saturday: Weak srn stream high pressure will cross
the region Tue and Wed. This will maintain rather nice conds as td/s
remain in the 40s Tue and only moderating into the 50s Wed. Along
with max temps right around or just a few degrees above normal...two
rather pleasant spring days look to be in store. Min RH values will
come close to fire wx concerns...and with localized deeper mixing
may reach 25 percent or less. However...fuel moisture levels are
running moderately high and shud/nt dry too much due to the
widespread precip expected Mon.

The next low/frontal system will develop out of the srn plains Wed
night and track right toward the FA. The models are still having
placement differences wrt to the sfc low and thus the
amount/coverage of precip into the area...so will keep pops in the
mid chance range for now. This system looks to be deeply moist and
will therefore have issues with instability...also deep layered
shear will be moderate at best. So not expecting too much besides
general thunder and decent rainfall rates...but it could become more
favorable for stg/svr storms as the details are figured out and
agreed upon by the models over the next couple days.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Cirrus slipping in under the ridge axis is
keeping the low stratus and fog potential somewhat reserved, but it
is still likely that we will see a narrow window of IFR cigs and or
vsby before daybreak at all TAF sites given the near-ground
moisture. Any restrictions will be quick to burn off this morning,
however, with VFR likely throughout after about 13Z or 14Z. S to SW
surface winds will continue throughout at 10 kt or less, with a few
low end gusts possible with mixing this afternoon. The main concern
will be the potential for isolated, but strong to severe,
thunderstorm development this afternoon and early evening. Chances
appear too low to mention anywhere but KAND, where a PROB30 will be
featured after 19Z.

Outlook: Patchy fog and low clouds will be possible again Sunday
morning around daybreak. Diurnally-based showers and thunderstorms
will be possible on Sunday afternoon. More organized thunderstorms
are likely on Monday with a passing cold front. Drier weather is
expected Tuesday through Wednesday.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High  84%     High  98%     High 100%     High 100%
KGSP       High  92%     High 100%     High 100%     High 100%
KAVL       High  96%     High  96%     High 100%     Med   76%
KHKY       High  95%     High  87%     High 100%     High 100%
KGMU       High  92%     High  96%     High 100%     High 100%
KAND       High 100%     High  99%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...SBK
NEAR TERM...HG
SHORT TERM...SBK
LONG TERM...SBK
AVIATION...HG



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