Severe thunderstorms impact portions of southeast Georgia January 21, 2012


Overview

On Saturday, January 21, 2012, a potent shortwave trough pushed across the southeast U.S. in the afternoon and off the coast in the late evening (image 1).  At the surface, temperatures across southeast Georgia were in the lower 70s and dewpoints were in the upper 50s by late Saturday afternoon. Though instability was not high at the time, strong shear and airmass modification ahead of a squall line enabled severe thunderstorms to develop and push into our southeast Georgia zones shortly after sunset. Several severe thunderstorm warnings were issued along with 2 tornado warnings.  The storms primarly produced hail up to golfball size but no reports of tornadoes or significant wind damage were received.

Analysis

A cold front pushed across the southeast U.S. on Saturday afternoon with a pre-frontal band of convection stretching from central South Carolina to southern Alabama (image 2). Instability was more than sufficient (i.e., most unstable CAPE 500-1500 j/kg) across an area from southern Alabama to south central Georgia to fuel these thunderstorms as they progessed southward into the evening (image 3).  In fact, an early morning sounding on Saturday, January 21 at Birmingham, AL revealed strong 0-6 km shear of 38 knots and most unstable CAPE value of about 1500 J/kg. Later analyses would reveal deep layer shear increased to 40-50 knots across southern Georgia in the afternoon. Thus, the main impacts with the thunderstorms would be locally gusty winds and hail due to the strong shear aloft and cold temperatures of -16 deg C at 500 mb based on sounding data.  Furthermore, due to low level helicity values of 200-250 m2/s2, rotating thunderstorms certainly could not be ruled out and isolated cells did show brief periods of low and mid level mesocyclones. Since deep layer moisture was fairly limited and the band of showers and thunderstorms were moving rapidly east to southeast at 30 to 40 mph, flooding concerns were not a factor during this event.

Storm reports and radar Imagery

Radar imagery at 7 pm Saturday evening showed a solid line of convection from southern South Carolina to southwest Georgia. The first report of severe hail came around 645 pm as a thunderstorm with supercell characteristics moved across northern Jeff Davis county (image 4).  Severe hail was reported northeast of Hazlehurst as the storm moved east to southeast around 35 mph. As the evening continued, these severe thunderstorms began to outrun the forcing aloft and higher instability and began to weaken. However, further west additional thunderstorms would fire in the moist and unstable airmass and again produced golfball size hail in Coffee county just after 8 pm Saturday (image 5).  No significant wind damage was reported during the event though radar velocities briefly showed enhanced downbursts. By late evening, with the loss of heating the shortwave trough moving away from the area, the thunderstorms showed more significant weakening and updraft strength and lightning activity diminished.

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE JACKSONVILLE FL
1047 PM EST SAT JAN 21 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0644 PM     HAIL             NE HAZLEHURST           31.87N 82.60W
01/21/2012  E1.00 INCH       JEFF DAVIS         GA   911 CALL CENTER

0645 PM     HAIL             9 N BAXLEY              31.90N 82.35W
01/21/2012  E1.75 INCH       APPLING            GA   EMERGENCY MNGR

            GOLFBALL SIZE HAIL REPORTED 9 MILES NORTH OF BAXLEY

0645 PM     HAIL             1 S HAZLEHURST          31.85N 82.60W
01/21/2012  E1.00 INCH       JEFF DAVIS         GA   PUBLIC

            QUARTER SIZE HAIL REPORTED AT 17 NORTH OSAGE LANE

0703 PM     HAIL             W BAXLEY                31.71N 82.40W
01/21/2012  E0.75 INCH       APPLING            GA   EMERGENCY MNGR

            DIME TO PENNY SIZE HAIL REPORTED WEST OF BAXLEY NEAR
            BUCKHEAD ROAD

0708 PM     HAIL             8 NNE BAXLEY            31.87N 82.30W
01/21/2012  E0.75 INCH       APPLING            GA   EMERGENCY MNGR

            DIME TO PENNY SIZE HAIL REPORTED 8.5 MILES NORTHEAST OF
            BAXLEY

0708 PM     HAIL             8 NNE BAXLEY            31.87N 82.30W
01/21/2012  E0.75 INCH       APPLING            GA   EMERGENCY MNGR

            DIME TO PENNEY SIZE HAIL REPORTED 8 MILES NORTHEAST OF
            BAXLEY

0720 PM     HAIL             5 S BAXLEY              31.69N 82.35W
01/21/2012  E1.75 INCH       APPLING            GA   EMERGENCY MNGR

            EMERGENCY MANAGEMENT RELAYED A REPORT OF GOLFBALL SIZE
            HAIL ALONG HIGHWAY 15.

0810 PM     TSTM WND DMG     NICHOLLS                31.52N 82.64W
01/21/2012                   COFFEE             GA   EMERGENCY MNGR

            TREE LIMBS WERE REPORTED DOWN.

0815 PM     HAIL             1 NNW DOUGLAS           31.52N 82.86W
01/21/2012  E1.00 INCH       COFFEE             GA   EMERGENCY MNGR

            QUARTER SIZE HAIL REPORTED NW OF DOUGLAS

 report by: A. Shashy


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.