Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 291736

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
136 PM EDT Sat Apr 29 2017

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


As of 10am EDT Saturday: Fog and low stratus is mostly clearing, and
ceilings will continue to improve as BL mixes out later this
morning.  High pressure and good insolation with partly cloudy skies
will lead to a substantial warming today with highs in the upper 80s
in Piedmont areas.  Warming will also allow CAPE values to reach
levels over 2000 j/kg this afternoon. Some capping and a lack of
forcing/focus will hold back any widespread convection.  Persistent
southerly flow will maintain BL dewpoints and will give some lift
over the mountains where the best chance of a convective shower will
exist.  Minimal vertical wind shear will make any thunderstorms
pulse in nature.  CAMS generally break-out some scattered to widely
scattered convection, mostly over the mountains, but some in
Piedmont areas where the cap could give way if there is sufficient
heating.  Given healthy CAPE levels, there may be a window for some
large hail or microburst winds around peak heating from 4pm to 8pm

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.


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.


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 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.


At KCLT and elsewhere:  Continued southerly to south-southwesterly
surface winds of 5 to 10 kts with a few gusts to 15 or 20 in the
mountains will maintain the moist low-levels of the atmosphere
through Sunday.  Currently have extensive SCT to BKN clouds with bases
around 2000 to 4000 ft AGL.  Model soundings have mixing with fair
weather cu bases up to 4500 ft this afternoon.  Some convective
showers may develop this afternoon/evening in areas west of I27.
Hi-res models have some scattered convection around peak heating,
but lack of upper support and low wind shear will limit severity.
Went with VCTS for KAVL and KAND, with the chances too low to
mention elsewhere.  Moist low-levels give a good chance for fog
again Sunday morning, and TAFS follow the general pattern of timing
that occurred this morning.  Possibly more high clouds Sunday
morning ahead of next system may reduce fog Sunday morning relative
to what was seen this morning.

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...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       High 100%     High 100%     High 100%     High  93%
KGSP       High 100%     High 100%     High 100%     Med   60%
KAVL       High 100%     High 100%     Med   66%     Med   78%
KHKY       High 100%     High 100%     Med   75%     High  85%
KGMU       High 100%     High 100%     High 100%     Med   68%
KAND       High 100%     High 100%     High 100%     Low   39%

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:




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