Severe Thunderstorm Warning 25, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
358 AM EDT Fri Apr 19 2019

.SYNOPSIS...
A strong cold front will move through the forecast area today
bringing showers and thunderstorms to the region. There is a
good chance that some of these storms could become severe as
the front moves through the area. Cooler temperatures and
lingering showers are expected behind the front. Temperatures
will warm again by early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 355 AM...The big story continues to be the dynamic upper low
pressing east into the Deep South and the associated severe weather
potential for our area later today. The latest radar showed an
organized line of convection (QLCS) stretching north to south from
the Gulf of Mexico into eastern TN. The upper low responsible for
this line of convection is expected to close off across northern MS
this afternoon before curling east and then northeast into the
southern to mid Appalachian mtns tonight. The closed low will slow
down somewhat while beginning to acquire a negative tilt. This will
likely do two things. One, it will provide a significant couplet of
strong synoptic ascending and descending air associated with a 120
kt jet streak overhead. Two, the slowing should allow for diurnal
instability (especially for the I-77 corridor) to be able to tap
into strong shear (0-1 km BS of 40+ kts) just above the surface (two
key ingredients for severe weather). The leading line of convection
(QLCS) looks to have the greatest widespread severe threat after 11
am with severe winds (in excess of 58 mph) the primary threat due to
the potential for a strong rear inflow jet associated with the QLCS
with a secondary threat for both tornadoes and severe hail. In fact
SPC has issued an moderate risk of severe weather for the I-77
corridor including Charlotte meaning that scattered severe
thunderstorms are likely. The severe risk gradually decreases
heading west across the FA. The mode of convection is more up for
debate after the initial line as model guidance does show a
secondary frontal feature following the main one, but the question
remains as to how much instability will be left and how any
convection may organize along or out ahead of it. Leaning towards
more disorganized convection moving generally SW to NE as llvl flow
veers to the SW with the upper low nearing the FA later this
afternoon. Can't rule out a few supercell thunderstorms developing
ahead or along the main line of convection (if there are breaks) or
mini super cells behind the system (mini due to the relative lack of
instability. The slow moving nature of convection with the main line
of convection in particular will likely cause at least some hydro
issues to small streams and roadways (WPC slight risk for excessive
rainfall across the region). The strong southerly winds along and
ahead of this system will support gusty winds across the high
elevations, especially SW mountains where a wind advisory has been
posted and continues through noon.

Most areas will see rain and thunderstorms come to an end by this
evening as the main forcing exits NE of the region. However, the
cold core upper low will support snow levels falling to around 4K
feet and potential for accumulating snows at this level with several
inches possible above 5K feet, especially where the best upslope
flow (from the SW) overlaps with good synoptic lift and moisture
across the SW mtns. As of now the main winter weather impacts appear
to be above 5K feet so any winter products will be shelved for now,
but considered on future shifts. Temps for most areas will only fall
into the 40s and 50s (30s higher mtn elevations) due to continued
breezy conditions, so frost should not be an issue.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 235 AM EDT Friday: the short-term fcst picks up at 12z on
Saturday with an impressive upper low centered just to our north
as steep upper ridging spreads over the Western CONUS. Because
this system is essentially cut-off from the northern-stream upper
flow, it will push eastward very slowly and is not expected to
move off the Atlantic Coast until the very end of the period on
Monday. At the sfc, a substantial low pressure system will be
centered to our NNW and over the Ohio River Valley as the cold
front associated with it moves offshore. Over the next 24hrs or
so, the low will remain nearly stationary as a substantial plum
of deep-lyr moisture spreads over much of the CWFA from the west.
The latest model guidance continues to open up the low by Sunday
morning as the system gradually lifts NE of the fcst area and
drier air moves back over the area. For the rest of the period,
drier high pressure centered over the Northern Gulf of Mexico
will persist over the Southeast. As for the sensible fcst, we
will likely have some lingering precip on Sat with the remainder
of the period being dry. With the impressive cold-air advection
expected across the region and unusually low thickness values,
some snow flurries are expected over the higher elevations early
Sat and early Sun. Some accumulating snow is possible above 3500
ft, with a better chance above 5000ft. At this time, I do not
anticipate any winter hazard products will be needed, but if
expected snow amounts trend upwards then hazards cannot be ruled
out. The resulting windy conditions should help inhibit any frost
formation across the active zones (which is everywhere except the
Northern NC Mountains). Temps should warm back into the upper 60s
to low 70s across the lower elevations on Sunday, with more warming
as we move into the extended period.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 245 PM EDT Thursday: Upper low over the Mid-Atlantic will
continue to lift north, with high pressure building in and
increasing thicknesses. Temperatures will increase through the
extended, 5 to maybe even 10 degrees above seasonal. A shortwave
spinning around the upper low may bring some showery activity or
even possible thunderstorms Tuesday afternoon, GFS a little stronger
with this idea than ECMWF. Next system gearing up over the Rockies
will push off into the Plains sometime midweek, but there are some
very significant timing differences between the global models, so
frankly opted to keep a fairly generic blend through the end of the
period and into the new day 7. As a note to readers, depending on
how near-term activity shapes up tonight, the extended forecast may
not be updated until Friday afternoon.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Rapidly deteriorating conds expected between
12Z and 18Z associated with a dynamic storm system to move through
the region. Model guidance shows that the strong line of showers and
thunderstorms (QLCS) approaching across the deep south will hold
together and even intensify east of I-26 and especially near the I-
77 corridor, including KCLT. Brief SW/W gusts in excess of 40 kts
is possible with the QLCS. Light to occasionally moderate LLWS is
possible, especially between 15Z and 20Z. LLWS issues may linger at
KAVL behind this time as winds veer to the SW. A secondary impulse
of showers and embedded thunderstorms associated with the leading
edge of the upper low are possible just about anywhere between 18Z
and 00Z.

Outlook: Improving conditions are expected early Saturday. Spotty
restrictions cannot be ruled out over the mtns as an upper low
passes by on Saturday.

Confidence Table...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       High  92%     High  81%     Med   77%     High  98%
KGSP       High  84%     High  90%     Med   65%     High  87%
KAVL       High  90%     Med   71%     Med   71%     High  87%
KHKY       High  86%     High  87%     High  89%     Med   72%
KGMU       High  84%     High  90%     Med   67%     High  87%
KAND       Med   79%     High  85%     High  81%     High  82%

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...Wind Advisory until noon EDT today for NCZ033-048>052-058-059-
     062>064.
SC...None.

&&

SYNOPSIS...JPT
NEAR TERM...Munroe
SHORT TERM...JPT
LONG TERM...TDP
AVIATION...Munroe

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
503 PM EDT Thu Apr 18 2019

GAZ010-017-NCZ033-048>053-058-059-062>065-501-503-505-507-509-
SCZ001>003-192115-
Rabun-Habersham-Avery-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-
Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Caldwell Mountains-Burke Mountains-McDowell Mountains-
Rutherford Mountains-Polk Mountains-Oconee Mountains-
Pickens Mountains-Greenville Mountains-
503 PM EDT Thu Apr 18 2019

This Hazardous Weather Outlook is for the mountains of northeast
Georgia, western North Carolina, and Upstate South Carolina.

.DAY ONE...Tonight.

Gusty winds from the south will develop across the high elevations
of the southern Appalachians tonight. Wind gusts of 40 to 50 mph
will be possible, mainly on exposed peaks and ridge tops. A band of
heavy rain showers and embedded thunderstorms is expected to move
into the mountains of the western Carolinas and northeast Georgia
between midnight tonight and daybreak Friday. The primary threat
from these showers and storms will be from very heavy rainfall
leading to rapid water rises on small streams and in areas of poor
drainage. Localized flash flooding will be possible. In addition,
brief, damaging wind gusts cannot be ruled out.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Gusty south winds and the threat for localized flash flooding will
continue into Friday. The potential for localized damaging winds
associated with heavy rain showers and thunderstorms is expected to
increase a bit during the daylight hours Friday.

.SPOTTER INFORMATION STATEMENT...

Spotters may need to forward reports of damaging winds or flooding to
our office on Friday.

GAZ018-026-028-029-NCZ035>037-056-057-068>072-082-502-504-506-508-
510-SCZ004>014-019-192115-
Stephens-Franklin-Hart-Elbert-Alexander-Iredell-Davie-Catawba-Rowan-
Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union-Greater Caldwell-
Greater Burke-Eastern McDowell-Greater Rutherford-Eastern Polk-
Greater Oconee-Greater Pickens-Greater Greenville-Spartanburg-
Cherokee-York-Anderson-Abbeville-Laurens-Chester-Greenwood-
503 PM EDT Thu Apr 18 2019

This Hazardous Weather Outlook is for the foothills and piedmont of
extreme northeast Georgia, western North Carolina, and Upstate South
Carolina.

.DAY ONE...Tonight.

Hazardous weather is not expected at this time.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

A band of heavy rain showers and embedded thunderstorms is expected
to move across the foothills and Piedmont from early Friday morning
through the afternoon. Isolated severe thunderstorms capable of
producing locally damaging wind gusts and isolated brief tornadoes
will be possible, especially across the Piedmont, from mid-morning
through the afternoon. In addition, localized excessive rainfall may
cause flash flooding of small streams and urban areas.

.SPOTTER INFORMATION STATEMENT...

Spotters may need to forward reports of damaging winds, tornadoes,
or flash flooding to our office on Friday.

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
506 AM EDT Fri Apr 19 2019

GAZ010-NCZ051-058-059-062>064-191000-
Rabun GA-Transylvania NC-Graham NC-Swain NC-Southern Jackson NC-
Northern Jackson NC-Macon NC-
506 AM EDT Fri Apr 19 2019

...HEAVY RAIN SHOWERS WITH EMBEDDED THUNDERSTORM WILL IMPACT NORTHERN
RABUN...MACON...SOUTHWESTERN TRANSYLVANIA...JACKSON...SOUTHWESTERN
SWAIN AND GRAHAM COUNTIES UNTIL 600 AM EDT...

At 504 AM EDT, Doppler radar was tracking isolated thunderstorms with
torrential rainfall southeast of Franklin, or 5 miles
northwest of Highlands, moving north at 45 mph.

Locations to be impacted include...
Franklin, Sylva, Bryson City, Robbinsville, Brevard, Cullowhee,
Highlands, Webster, Dillard and Sky Valley.

Wind gusts up to 40 mph and very heavy rainfall rates up to 2 inches
per hour will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

The combination of gusty winds and saturated soil conditions will
cause scattered trees and power lines to fall. Seek shelter inside an
interior room.

&&

LAT...LON 3544 8399 3555 8378 3533 8296 3529 8292
      3531 8288 3526 8271 3497 8312 3494 8360
      3495 8355 3499 8355 3499 8349 3500 8352
      3515 8365 3515 8374 3523 8369 3526 8371
      3522 8397 3524 8401 3535 8404
TIME...MOT...LOC 0904Z 193DEG 39KT 3510 8329

KRENTZ