Special Weather Statement, NWS Columbia, SC

Area Forecast Discussion
National Weather Service Columbia SC
215 PM EDT Sat Jun 23 2018

.SYNOPSIS...
High pressure will extend from the Atlantic westward into the
Gulf of Mexico through Sunday. North of the ridge a weak trough
will be in the forecast area. The pattern supports hot conditions
with scattered thunderstorms. A backdoor cold front will move
into the region Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Surface high pressure will extend from the Atlantic westward
into the Gulf of Mexico through tonight. North of the ridge
lee-side troughing will be in the forecast area. The air mass is
moist and becoming possibly becoming strongly unstable with ML
CAPE above 2500 J/kg by late this afternoon. Of concern is a
mesoscale convective system (MCS) moving east across northern
Alabama at 17z. Other storms to the east of ATL moving toward
the CSRA. Don't think models have been handling the MCS and weak
embedded short wave troughs. Deep layer shear appears
marginally strong although may increase as MCS approaches.
Soundings suggest wind threat with inverted V and relatively
high DCAPE around 1000 J/kg. SPC has area in marginal risk
Severe thunderstorms The latest HRRR and other high resolution
models tend to favor the CSRA through early evening for
scattered to possibly numerous showers and thunderstorms
although given recent radar trends, scattered thunderstorms
possible in the Midlands by early this evening. The Nam model
suggests convection will weaken in the Midlands by late evening
as nocturnal cooling develops and instability weakens. Raised
pops especially south of CAE for late afternoon and early
evening. Given weak to moderate instability overnight kept
threat of widely scattered showers late into the evening.

It will be hot today with highs in the middle and upper 90s.
Expect peak heat index values around 102.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
A mid-level ridge will build into the area Sunday and Monday
with 850 mb temps from 20 to 22 degrees C. Temperatures will be
above normal with highs in the upper 90s to around 100 degrees
and lows in the mid 70s. Heat index values will likely range
from 105 to 110 with the warmer values in the CSRA where
surface dewpoints will be higher. A heat advisory may be needed
for one or both of these days.

Subsidence due to weak high pressure, westerly downslope flow, and
a mid-level capping inversion will hinder convective development
on Sunday. Therefore, only expect isolated shower and thunderstorm
coverage in the afternoon. The best chance for scattered thunderstorms
will be in the evening as a shortwave moves through the region.
Instability will naturally diminish after sunset, but bulk shear
will be around 25 kts, so a few stronger storms will also be
possible, with damaging wind the biggest threat.

On Monday, a cold front will move into the region. The front
will likely remain north of the forecast area during the day,
continuing the trend of well above normal high temperatures,
although it will likely be a few degrees cooler than Sunday. As
the front sags southward on Monday evening, another shortwave
will accompany it, with scattered thunderstorms that could
persist through much of the night.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
The front is expected to stall just south of the area on
Tuesday, then wash out by Wednesday. Due to increased cloud
cover and slightly cooler air behind the front, temperatures
will be closer to normal on Tuesday and Wednesday, with highs in
the low 90s. There is a good chance of scattered thunderstorms
on Tuesday, with lesser chances Wednesday and Thursday due to
high pressure ridging, but cannot rule out diurnal convection.
Onshore flow and moisture will increase on Friday and Saturday,
so precipitation chances will also increase going into next
weekend. Basically, showers and thunderstorms will be possible
each day. However, exactly when and where the most potent storms
will hit cannot be determined with certainty at these time
ranges.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
Expect mainly VFR conditions during the 24-hour TAF period but
there will be a chance of thunderstorms especially at the AGS
and DNL terminals this afternoon and evening.

Showers and thunderstorms over Alabama and Georgia upstream of
the terminals associated with mesoscale convective system (MCS).
Air mass becoming strongly unstable. Strongest forcing appears
to be across the CSRA at least late this afternoon and early
evening...so mention tempo thunderstorms at the CSRA terminals.
Otherwise scattered to broken cumulus this afternoon with
increasing mid level clouds. Gusty west-southwest winds due to
25-30 kt 850mb jet. Winds diminishing after 00z. Nocturnal
cooling should result in more limited convection after 03z by
slight chance shower or thunderstorms through at least 06z. VFR
conditions through early morning as instability and mixing
limiting the risk of fog.

EXTENDED AVIATION OUTLOOK...Restrictions possible each day in
early morning fog and afternoon and evening thunderstorms.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.

&&

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Special Weather Statement
National Weather Service Columbia SC
406 PM EDT SAT JUN 23 2018

SCZ018-025-232030-
McCormick SC-Edgefield SC-
406 PM EDT SAT JUN 23 2018

...Strong Thunderstorms Will Impact Portions of northern McCormick
and Edgefield Counties Until 430 PM EDT....

...Boaters on Lake Strom Thurmond Should Seek Safe Harbor...

At 405 PM EDT...National Weather Service doppler radar indicated
strong thunderstorms along a line extending from 8 miles west of
McCormick to near Edgefield, moving east at 25 mph.

  HAZARD...strong winds 45 to 55 mph and pea sized hail.

  IMPACT...expect minor damage to tree limbs and blowing around of
           light, unsecured objects. Minor hail damage to plants,
           trees and crops is possible. Damage to windshields is
           unlikely.

Some locations in the path of these storms include...
Edgefield, McCormick, Johnston, Trenton, Bradley, Plum Branch and
Willington.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Boaters on Lake Strom Thurmond should move to shore and seek shelter.
Strong, erratic wind gusts and lightning are possible. If you can
hear thunder, you are close enough to be struck by lightning.

These storms may intensify. Monitor NOAA Weather Radio, local radio
and television stations for additional information and possible
warnings from the National Weather Service.

&&

LAT...LON 3402 8232 3397 8230 3402 8224 3397 8218
      3399 8215 3398 8206 3398 8205 3395 8204
      3396 8201 3391 8187 3389 8187 3386 8183
      3381 8166 3370 8180 3369 8190 3394 8253
TIME...MOT...LOC 2005Z 277DEG 22KT 3393 8243 3381 8190

JAQ

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