Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
752 PM EDT Sun Apr 30 2017

.SYNOPSIS...
A cold front will approach the Western Carolinas later tonight and
move across the forecast area on Monday with strong to severe
thunderstorms possible as it does. Dry, weak high pressure builds
across the southeast Tuesday through Wednesday. On Thursday and
Friday, a moist area of low pressure will lift across the region
from the southwest.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 745 PM EDT Sunday:  Updated discussion for taf issuance.
Did tweak pops/t/td in the immediate near term to account for
iso/sct shra and or tsra spread along the I85 corridor, however
continuing to favor a lowering trend over the next few hours as
instability is lost given cooling.  Otherwise, the approaching
prefrontal band of convection, now moving into the TN Valley,
should weaken as it encounters more stable air as well as terrain.
That said, did shift pop maxima along the TN line and NC high
terrain, however maxing out in the mid/high chance range.
Otherwise, no sig changes made for this update.

Previous Discussion: A few elevated showers have popped-up in the
last hours.  These showers are moving almost due north and have
had no lightning so far.  With CAPE analyzed at 500 to 1000 j/kg,
it is possible one or two of these showers will intensify into
a thunderstorm this afternoon before this diurnal activity fades
at sunset.

Due to more extensive cloud cover, highs are running around 5
degrees below yesterday, though did increase temps a degree or so
with this update as clouds were opening some.  Reduced temperatures
will limit CAPE and the chances for any significant precip today,
but precip. becomes likely as major front approaches late tonight
and tomorrow from the west.

Area is currently in a well-defined and large warm sector ahead
of major frontal system currently stacked over the south-central
CONUS.  Cold front with line of convection is currently moving
through LA into MS.  Latest timing has front into the GSP CWA
early Monday morning, passing through by late Monday afternoon.
Significant precipitation/thunder is expected near and along the
front.  Passage of cold front will cool temps and scour moisture,
ending immediate chances for precip. Main question with this event
will be the chances for severe weather.  Instability and wind shear
are both in the moderate range with 30 to 40 kts of bulk shear and
LI to -5 Monday afternoon.  Shear is much better further north,
but combination of ingredients should be enough for at least some
severe weather on Monday, with wind gusts in bowing segments of
expected QLCS-type system.  An isolated, brief tornado is not
out of the question, but alignment of shear direction with front
orientation favors QLCS and non-super-cellular storms.

850mb flow will also be quite strong with passage of the front,
with southerly to southwesterly winds of 40 to 55 kts from tonight
through Monday.  Surface winds are not expected to reach advisory
levels, except possibly at the highest elevations, and have declined
to issue a product for wind at this time.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 120 PM EDT Sunday: a considerably more tranquil weather
scenario is expected for the middle of the week. The back edge
of the precip associated with the cold front might still be over
the eastern-most zones at sunset on Monday, but that should move
away to the east in short order. The upper low lifting NE of the
Gt Lakes on Monday night should allow for the upper trof to the
west to deamplify through Tuesday, resulting in a nearly zonal
upper pattern thru Tuesday night. With that, we welcome weak high
pressure that should bring sunny sky, normal temperatures, and a
dry air mass that will result in a nearly perfect spring day on
Tuesday. The weak high will move to our east on Wednesday as the
upper pattern buckles with the next upper trof digging over the Srn
Plains. That should start a return flow of moisture from the Gulf
ahead of the system late in the day. However, present indication
in the model data is that moisture/precip will not arrive before
the end of the daytime period on Wednesday. That should give us
another mostly dry day with some increasing clouds in the afternoon,
and temps creeping up a bit above normal.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 235 PM EDT Sunday: still looking at the development of
another weather system for the late part of the week, but right
now that system remains a moving target. The main issue appears to
be when/where the upper trof cuts off a low.  Will it be Thursday
morning over the Ozark Plateau per the GFS, or the lower OH Valley
Thursday night as in the new ECMWF? Either way, we are looking at
significant moisture transport from the Gulf of Mexico ahead of the
system and lifting northeast across the western Carolinas beginning
Wednesday night. See no problem as the models agree in principle
of providing a wet period centered mainly on Thursday/Thursday
night, so precip probability is ramped up to the likely range
across the whole fcst area. Have resisted the temptation to go
categorical for now, given the run-to-run consistency issues with
the details of this system. The main issue with the guidance creeps
in on Friday and that deals with how quickly the system moves
past. The op GFS remains the slower solution with the center of
the low moving slowly from the Cumberland Plateau to the Central
Appalachians Friday through Saturday morning. Even if the slower
solution comes to pass, most of the area east of the mtns would
develop a downslope flow Friday night that would limit additional
precip, while a more NW flow would enhance or maintain precip
chances near the TN border. The precip probs will be moved in that
direction. Temps should stay below normal Thursday through Saturday
with the extensive cloud cover and threat of precip. Expect the
system to lift out in time Sunday to salvage half the weekend,
with some clearing and temperatures returning to normal.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
At KCLT and Elsewhere:  Mostly VFR through the first half of
the taf cycle, with the exception of brief cig/visb reductions at
KGSP/KGMU given sct shra/tsra currently moving through the Upstate.
Otherwise, guidance favors lowering of cigs overnight as moisture
increases ahead of an approaching cold front.  A prefrontal band
of convection working through the TN valley at this time will
likely weaken as it moves east into diurnally cooling/stabilizing
air through the evening into the early morning.  With that,
few residual shra cannot be ruled out at KAVL and the SC sites,
perhaps as far east as KHKY as well through daybreak.  The biggest
impact from this will be lowering cigs, likely into the MVFR/IFR
and perhaps LIFR range.  Beyond that, convection will ramp up yet
again into the late morning hours across the western tier of the
fcst area as the front moves in, with destabilization underway out
ahead across the NC Piedmont and SC Upstate.  Expecting rather
robust tsra into the later part of the taf cycle with some svr
storms possible, thus did prevail tsra at all sites with timing
based upon camguide.  Light/moderate sly/swly winds will prevail
through the period with some gusting likely on Monday, gradually
veering at the westernmost sites post fropa.

Outlook: Behind the cold front exiting by Monday afternoon,
drier weather is expected Tuesday. A return of afternoon/evening
thunderstorms is possible Wednesday, while another cold front may
bring another round of widespread showers and storms by Thursday
into Friday.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High  93%     High  96%     High  82%     High  85%
KGSP       High  95%     High  95%     High  99%     High  94%
KAVL       High  85%     High  80%     High  89%     High  97%
KHKY       High  94%     High  91%     High  90%     High  89%
KGMU       High  97%     High  97%     High  93%     High  96%
KAND       High  96%     High  96%     High  92%     High  96%

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...JPT
NEAR TERM...CDG/WJM
SHORT TERM...PM
LONG TERM...PM
AVIATION...CDG

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
427 AM EDT Sun Apr 30 2017

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-010830-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Avery-Alexander-
Iredell-Davie-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-Catawba-
Rowan-Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-Rutherford Mountains-
Greater Rutherford-Polk Mountains-Eastern Polk-Oconee Mountains-
Pickens Mountains-Greenville Mountains-Greater Oconee-
Greater Pickens-Greater Greenville-Spartanburg-Cherokee-York-
Anderson-Abbeville-Laurens-Chester-Greenwood-
427 AM EDT Sun Apr 30 2017

This Hazardous Weather Outlook is for northeast Georgia, piedmont
North Carolina, western North Carolina and upstate South Carolina.

.DAY ONE...Today and Tonight.

Isolated to scattered thunderstorms will develop across the western
Carolinas and Northeast Georgia this afternoon. These storms will be
capable of producing cloud to ground lightning, small hail, and
localized gusty winds.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

..Monday...Severe weather possible. A cold front will cross the area
on Monday possibly producing organized strong to severe thunderstorms.
The greatest threats will be large hail and damaging winds, mainly
over the foothills and Piedmont of the Carolinas and northeast
Georgia in the afternoon and evening.
..Tuesday...No hazardous weather is expected at this time.
..Wednesday...No hazardous weather is expected at this time.
..Thursday...No hazardous weather is expected at this time.
..Friday...No hazardous weather is expected at this time.
..Saturday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

Krentz

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
821 PM EDT SUN APR 30 2017

NCZ508-510-SCZ007-010045-
Greater Rutherford NC-Eastern Polk NC-Spartanburg SC-
821 PM EDT SUN APR 30 2017

...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN RUTHERFORD...
SOUTHEASTERN POLK AND NORTH CENTRAL SPARTANBURG COUNTIES UNTIL 845 PM
EDT...

At 820 PM EDT, Doppler radar was tracking a strong thunderstorm 12
miles southwest of Forest City, or 6 miles northeast of Lake Bowen,
moving northeast at 30 mph.

Locations to be impacted include...
Forest City, Rutherfordton, Spindale, Lake Bowen, Green Creek,
Harris, Fingerville, Caroleen and Henrietta.

Wind gusts up to 50 mph will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Gusty winds can blow down trees that are dead, or that have weakened
root systems. Outdoor furniture and similar items can be tossed
around if not anchored. Seek shelter indoors.

&&

LAT...LON 3508 8199 3514 8210 3540 8195 3530 8176
TIME...MOT...LOC 0020Z 214DEG 27KT 3518 8199

LANE