Severe Thunderstorm Warning 61, NWS Columbia, SC

Area Forecast Discussion
National Weather Service Columbia SC
204 PM EDT Mon May 1 2017

.SYNOPSIS...
A cold front will cross the region this evening bringing showers
and thunderstorms to the area. Cooler high pressure will build
in behind the front tonight through midweek. Another
significant weather system will impact the region Thursday into
Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Strong upper level low continues to lift north into the western
Great Lakes region while a strong cold front currently extends
from eastern Tennessee through central Georgia. Regional radar
showing a line of showers and isolated thunderstorms just ahead
of the frontal boundary from Upstate SC southward into east
central GA. Overall convection to this point has been
surprisingly underwhelming given the shear in place which is
strong, southerly 45 knot 850mb jet and moderate instability
with LI values around -5C. Still expect additional development
of the line of convection pushing into our forecast area later
today with a squall line type feature providing a damaging wind
gust threat. Cannot rule out the possibility of an isolated
weak tornado if there is a break in the line. Timing has not
changed much overall either, 3-5pm for western Midlands and
upper CSRA, central Midlands and CSRA including Columbia and
Augusta 4-7pm and eastern Midlands 5-8pm. Precipitable water
values are very high just ahead of the front around 1.8 inches
which would support a heavy rain threat but think the storms
will have enough movement to minimize that threat although urban
areas which have poor drainage could see some minor issues.

Lake wind advisory remains in effect through 8pm. The cold front
will push across the region this evening and storms should exit
the forecast area by 9pm with clearing expected overnight.
Winds will stay up overnight limiting radiational cooling but
there will be some cool advection which will support lows in the
50s to around 60 degrees.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
A zonal flow aloft will prevail across the Southeast U.S. Tuesday
through Wednesday.  Dew point temperatures drop into the 40s which
will allow overnight lows to dip into the 50s. Highs will be near
normal both days.

The next closed upper level low pressure system drops into the Mid
South on Thursday which pushes a cold front through the CSRA and
Midlands late Thursday afternoon into Thursday Night. Surface based
CAPE values may be up to 750 J/KG ahead the front and passage occurs
after peak diurnal heating.  That being said, the shear is quite
impressive with 0-1 km helicity values up to 300 m2/s2.  Strong to
severe thunderstorms will be possible.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
The Midlands and CSRA are forecast to be in the "dry slot" of the
aforementioned upper low Friday into Saturday. It will be breezy to
windy with below normal temperatures.  There is a low chance of a
thunderstorms on Friday. The upper low pulls farther away into
Quebec early next week which will allow winds to subside and
temperatures to warmer closer to climatology for early May.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
A cold front will push across the region this evening with
showers and thunderstorms along and ahead of the front. Cigs
have become VFR all terminals early this afternoon and should
remain VFR throughout the forecast period outside of possible
MVFR/IFR vsbys within storms. Tried to time the window of a
possible squall line impacting terminals from west to east
generally in the 19z-24z time frame.

Conditions should improve behind the front this evening with
clearing skies. Strong southerly winds today ahead of the front
will shift to the southwest and west overnight behind the front.
Winds will pick back up after 15z Tuesday with a westerly
direction and gusts to around 20 knots.

EXTENDED AVIATION OUTLOOK...Visibility and ceiling restrictions
will be possible Thursday through Friday in showers and
thunderstorms.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...Lake Wind Advisory until 8 PM EDT this evening for GAZ040-
     063>065-077.
SC...Lake Wind Advisory until 8 PM EDT this evening for SCZ015-016-
     018-020>022-025>031-035>038-041.

&&

Hazardous Weather Outlook
National Weather Service Columbia SC
336 AM EDT Mon May 1 2017

GAZ040-063>065-077-SCZ015-016-018-020>022-025>031-035>038-041-020745-
Lincoln-McDuffie-Columbia-Richmond-Burke-Lancaster-Chesterfield-
McCormick-Newberry-Fairfield-Kershaw-Edgefield-Saluda-Lexington-
Richland-Lee-Aiken-Sumter-Barnwell-Orangeburg-Calhoun-Clarendon-
Bamberg-
336 AM EDT Mon May 1 2017

...LAKE WIND ADVISORY IN EFFECT FROM 10 AM THIS MORNING TO 8 PM EDT
THIS EVENING...

This Hazardous Weather Outlook is for the Midlands of South Carolina
and the Central Savannah River area of Georgia.

.DAY ONE...Today and Tonight.
Moderate to strong instability and shear will occur ahead of a cold
front today. Thunderstorms with damaging wind and hail may occur. A
tornado is possible. Expect a fast storm movement with a diminished
flood threat. However, very heavy downpours may occur with possible
localized flooding in flood-prone locations if cell training happens
to occur. Based on the high-resolution models the strongest
convection may move into the west part of the outlook area around
200 pm. The most likely timing in Augusta may be 300 pm to 500 pm,
and in Columbia 400 pm to 600 pm. The strongest storms may extend
through the eastern Midlands 600 pm to 800 pm.

Also, please listen to NOAA Weather Radio or go to weather.gov on
the Internet for more information about the following hazard.

   Lake Wind Advisory.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Strong instability and shear along with high moisture may be
associated with another system supporting possible severe
thunderstorms and localized flooding Thursday and Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be required this afternoon.

Special Weather Statement
National Weather Service Columbia SC
221 PM EDT MON MAY 1 2017

GAZ040-063-064-SCZ018-011845-
McDuffie-Lincoln-Columbia-McCormick-
221 PM EDT MON MAY 1 2017

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT NORTHWESTERN
COLUMBIA...MCDUFFIE...LINCOLN AND NORTHWESTERN MCCORMICK COUNTIES...

At 219 PM EDT, radar indicated strong thunderstorms were located
along a line extending from near Washington to 7 miles north of
Deepstep. Movement was northeast at 40 mph.

Winds around 40 mph are possible with these storms.

Locations impacted include...
Thomson, McCormick, Lincolnton, Lake Strom Thurmond, Willington and
Mount Carmel.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

LAT...LON 3364 8261 3363 8258 3365 8258 3364 8256
      3365 8249 3383 8260 3386 8257 3386 8261
      3393 8263 3396 8257 3406 8244 3406 8233
      3397 8230 3402 8225 3399 8222 3333 8243
      3334 8250 3336 8255 3341 8255 3360 8265
TIME...MOT...LOC 1819Z 236DEG 35KT 3380 8276 3312 8298

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