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Area Forecast Discussion

FXUS62 KGSP 280127

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
927 PM EDT MON JUN 27 2016

A weak cold front will push slowly across the area tonight through
Tuesday. Weak high pressure should build in from the north for the
middle to latter part of the week. Another cold front is expected to
push into the area over the weekend.


0130 UTC Update: Winds were updated with a blend of the latest NAM
and ADJMAV guidance. Pops and QPF were adjusted per radar trends,
favoring the Blue Ridge and the Interstate 77 corridor. Only minor
changes were made to temperatures and dew points.

As of 250 pm, scattered to numerous showers and thunderstorms were
located across the east facing mtn slopes, the upper Savannah River
Valley, and the upstate of SC west of I-26. The convection was
developing within a larger pool of CAPE of 1500-2500 J/kg. DCAPE
across the region is generally weak, 500 J/kg across the mtns to
1000 J/kg across the Lakelands of SC. Corfidi vectors indicate that
the storms will favor a west to east track, speeds expected to range
from 10 to 20 kts. This environment should support the convection to
slide or develop east of the mtns through the afternoon and into the
evening hours. These storms may result in isolate wet microbursts
and pockets of heavy to excessive rainfall. NAM guidance indicates
that a second band of convection over middle KY/TN will cross the
mtns late this evening into early Tuesday morning. This activity may
remain largely intact across the mtns, but should fade east. I will
indicate likely POPs well into this evening along and north of I-85.
Low temperatures tonight are forecast to range from the mid 60s
across the mtns to around 70 east. Early morning fog will be
possible over areas wet ground across the mtns and foothills.

Tuesday, a second and stronger cold front will approach the forecast
area during the daylight hours. Morning convection will slide off to
the east. Later in the afternoon, a few new showers and
thunderstorms are forecast to develop over the mtns and slide east.
I will indicate falling PoPs through the day, but will keep schc
PoPs to cover afternoon convection. Instability is forecast to
remain limited to less than 1500 J/kg, supporting general storms.
Highs are forecast to range from the low 80s within the mtn valleys
to the mid to upper 80s east.


As of 130 PM Monday, surface boundary will remain south/east of the
area through the short term, with the axis of the upper trough
positioned over the region. Nevertheless, the air mass north/west of
the front will modify rather quickly, with short term guidance
depicting at least moderate instability across much of the forecast
area each afternoon. Lee trough and terrain effects will act as a
focus for initiation of isolated/widely scattered diurnal convection
Wed and Thu afternoon/evening. Chances for severe convection, even
of the pulse variety appear quite small due to modest bouyancy.
Temps will be very close to climo through the period.


As of 145 PM Monday, a gradual pattern change is expected during the
medium range, with low amplitude troughing likely becoming displaced
by a ridge building into the region from the southwest by Day 7.
Another standard issue/diurnal convective day is in the offing for
Friday. However, convective chances are expected to increase Fri
night through the early part of the weekend, as a short wave digging
across the Great Lakes briefly amplifies the Eastern trough.
Attendant frontal boundary is expected to push into the forecast
area Saturday afternoon, providing a focus for better coverage of
showers and storms, and warranting a 40-60 pop across much of the
forecast area.

Uncertainty increases toward early next week, as substantive
differences exist among the global models regarding the progression
of the frontal boundary toward the Southeast coast. Specifically,
the ECMWF is much more progressive, indicating drying/diminishing
chances for convection early next week. Meanwhile, the GFS tends to
hang the boundary up close enough to the forecast area to suggest
good chances for convection persisting through the end of the
period. Due to this uncertainty, have opted to allow the forecast to
trend toward a more typical diurnal convective cycle, with
near-climo pops early next week. Temps will begin the period a few
degrees above climo, before dropping back to normal in the vicinity
of the front for Days 6/7.


At KCLT: Convection will be slow to diminish and move out of the area
early this evening, and should increases again in the morning as a
cold front arrives. Guidance favors MVFR vsby around dawn. A
guidance blend favored a low VFR cig until late tonight, then MVFR,
returning to low VFR by midday. Winds will favor the south southeast
overnight. Guidance suggests winds veering to the northwest by
midday Tuesday as the front arrives, but with slow frontal
movement, veering may not occur until late.

Elsewhere: Another round of convection will move over the mountains
this evening, with the greatest impact on KAVL, although the
foothills sites may well be impacted. A relative lull is expected
overnight, but as a cold front approaches in the morning, convective
chances ramp up. Guidance favors MVFR vsbys around dawn, and MVFR
ceilings, falling to IFR in NC around dawn, and perhaps LIFR at
KAVL. Cigs return to low VFR by midday, and perhaps even high VFR
Tuesday afternoon.

Outlook: Diurnally favored shra/tsra will return mid/late week.
Flight restrictions will be possible during any TSRA. In addition,
morning fog maybe possible over areas of recent rainfall.

Confidence Table...

            01-07Z        07-13Z        13-19Z        19-00Z
KCLT       High 100%     High  83%     High  84%     High 100%
KGSP       High 100%     High  88%     High 100%     High 100%
KAVL       High  97%     Med   77%     High  88%     High 100%
KHKY       High  93%     High  82%     High  93%     High 100%
KGMU       High 100%     High  81%     High 100%     High 100%
KAND       High 100%     High  93%     High 100%     High 100%

The percentage reflects the number of guidance members agreeing
with the schedule 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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