Special Weather Statement, NWS Atlanta, GA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
1026 AM EDT SAT JUN 11 2011

.UPDATE...
CU ALREADY DEVELOPING...WHICH IS AHEAD OF YESTERDAY AND MORE LIKE
THURSDAY. GFS/RUC/HRRR ALL INDICATE GOOD COVERAGE OF
THUNDERSTORMS THIS AFTERNOON. WILL THEREFORE INCREASE POPS TO HIGH
CHANCE FOR THIS AFTERNOON AND ADD WORDING OF HEAVY RAIN AS STORMS
WILL NOT BE MOVING MUCH AS WELL AS HIGH K INDEX VALUES. NO OTHER
CHANGES PLANNED.

&&

.PREV DISCUSSION... /ISSUED 725 AM EDT SAT JUN 11 2011/

SHORT TERM /TODAY THROUGH MONDAY/...

STORMS CONTINUE AT THIS HOUR...FEEDING OFF NARROW STRIP OF 1000 TO
1500 J/KG MIXED LAYER CAPE FROM NE GEORGIA TO JUST NORTH OF
COLUMBUS. THESE VALUES ARE DOWN FROM AFTERNOON HIGHS AND HAS
RESULTED IN LESS ROBUST CONVECTION WITH JUST A FEW STRONG STORMS
NOTED SINCE MIDNIGHT. OVERALL TREND IN SHORT TERM MODELS IS FOR
ACTIVITY TO CONTINUE ITS DOWNWARD TREND INTO THE REMAINDER OF THE
OVERNIGHT PERIOD. OTHERWISE...MSAS ANALYSIS INDICATES A CONTINUED
VERY WEAK FLOW PATTERN IN PLACE WITH RIDGE OFF THE ATLANTIC COAST
INTO SOUTHEAST GA AND STILL INDICATIONS OF A WEAK TROUGH OVER
NORTHWEST SECTIONS OF THE FORECAST AREA...LIKELY AIDING INITIATION
OF STORMS.

FOR TODAY...MODELS INDICATE A NEARLY IDENTICAL PATTERN FOR STORM
COVERAGE AS WHAT WE SAW TODAY. RIDGE AXIS DOES TRY TO PUSH A
LITTLE FURTHER INLAND WHICH WOULD ALLOW FOR DRIER AIR TO CUTOFF
MORE OF THE FORECAST AREA FROM PRECIP CHANCES. SHOULD BE A SHARP
GRADIENT TO POPS AS LATE DEVELOPING SEABREEZE PUSHES IN AND ALONG
WITH AFOREMENTIONED TROUGH FORMS A STRONG CONVERGENCE ZONE OVER
NORTHWEST GA. RECENT MODEL TRENDS SHOW THIS OCCURRING FROM AHN TO
ATL AND SOUTHWEST AS OPPOSED TO THE FAR NW CORNER. WILL THEREFORE
ADJUST POPS TO REFLECT HIGHEST COVERAGE (35 TO 40%) SLIGHTLY TO
THE SOUTH OF PREVIOUS FORECAST. GETTING SIMILAR CAPE VALUES OFF
THE GFS BUFR SOUNDINGS WHICH ARE NON IMPRESSIVE FOR THIS TIME OF
YEAR. STILL EXPECT ISOLATED STRONG TO PERHAPS A SEVERE
THUNDERSTORM WITH THE MORE ROBUST ACTIVITY.

SUNDAY WILL BE THE FIRST DAY IN QUITE A WHILE IN WHICH WE ACTUALLY
SEE INFLUENCES FROM NORTHERN STREAM UPPER LEVELS AS RIDGE AXIS IS
SHUNTED WESTWARD. AT THE SURFACE...1020 MB HIGH BUILDING OVER THE
OHIO VALLEY WILL BRIDGE EASTWARD ALLOWING FOR A TROUGH OF LOW
PRESSURE TO ENTER OUR FORECAST AREA. INCREASING MOISTURE ALONG
WITH CONVERGENCE GENERATED ALONG THE TROUGH AS WELL AS HINTS OF
SHORTWAVE ENERGY DURING THE AFTERNOON ALL POINT TO INCREASED RAIN
CHANCES. WILL CARRY GENERIC 40 PERCENT AREAWIDE FOR NOW AND LATER
SHIFTS REFINE FURTHER.

BIGGEST CHANGE IN THE SHORT TERM IS THE GFS NOW COMING AROUND TO
FAVOR EARLIER NAM AND ECMWF SOLUTIONS OF BRINGING FRONT AND
ASSOCIATED DRY AIR ALL THE WAY THROUGH THE FORECAST AREA ON
MONDAY. THIS WOULD ACT TO SUPPRESS ANY AND ALL CONVECTION FOR MON
AFTERNOON AND AT THIS POINT WILL LEAVE GRIDS POP FREE.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...

DIFFICULT TO ASCERTAIN HOW EARLY NEXT WEEK IS GOING TO BE AS
MOISTURE LOOKS TO BE VERY LIMITED BUT NORTHWEST FLOW ALOFT
PROMISES INCREASED MID LEVEL ENERGY FOR POTENTIAL STORMS TO FEED
OFF OF. FOR NOW WILL FAVOR THE OVERNIGHT IN THIS SETUP WITH JUST
20 PERCENT FOR THE NORTHERN ZONES. BETTER CHANCES ON WED AND THU
AS ZONAL FLOW ALOFT DEVELOPS INTO A BROAD EAST COAST TROUGH.

23

AVIATION...
12Z UPDATE...
AGAIN TODAY...MAIN ISSUE THIS TAF VALID PERIOD WILL BE ISOLD-SCT
AFTERNOON/EVENING CONVECTION. WEAK WIND CONVERGENCE BOUNDARY WILL
LINGER FROM SW-NE NEAR A CSG-ATL-AHN LINE AND IS EXPECTED TO BE THE
FOCUS FOR AFTERNOON/EVENING CONVECTIVE DEVELOPMENT. COVERAGE AT PEAK
SHOULD BE IN THE 30-40 PERCENT RANGE. LESS THREAT FOR CONVECTION
TOWARD MCN TODAY...BUT BOUNDARY PROGGED TO DRIFT SE TOWARD CSG-MCN
OVERNIGHT. CONVECTION MAY PERSIST WELL INTO THE OVERNIGHT
HOURS...PER GFS. OTHERWISE...GENERALLY VFR WITH SCT 060-070CU/TCU
OUTSIDE AFTERNOON/EVENING CONVECTION. EARLY MORNING AREAS OF MVFR BR
HZ...OTHERWISE VFR VSBY OUTSIDE AFTN/EVE TSRA. WIND FIELD IS LIGHT
AND NOT AS DEFINITIVE AS FRI. HOWEVER...AFTN SEA BREEZE ADVECTING NW
INTO THE CWA SHOULD KEEP A SE WIND IN PLACE 6-8KTS THROUGH AT LEAST
MID-DAY. OVERNIGHT...MODELS AT ODDS IN DEVELOPING NW SFC FLOW. NAM
SEEMS TO HAVE A BETTER HANDLE ON THIS...SO HAVE OPTED FOR LIGHT/VRB
WINDS OVERNIGHT OR CALM...BECOMING W-WNW AFT 12Z SUN.

//ATL CONFIDENCE...
12Z UPDATE...
HIGH CONFIDENCE ON CIGS AND VSBYS THROUGH TAF VALID PERIOD.
MEDIUM CONFIDENCE ON TIMING AND COVERAGE OF TSRA.
MEDIUM CONFIDENCE ON WIND DIR...HIGH CONFIDENCE ON WIND SPEED
THROUGH TAF VALID PERIOD.

19

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          94  67  95  67 /  50  20  40  30
ATLANTA         93  72  91  70 /  50  20  40  30
BLAIRSVILLE     84  66  85  60 /  50  30  40   5
CARTERSVILLE    94  64  93  63 /  50  30  40  20
COLUMBUS        96  71  96  71 /  50  20  40  30
GAINESVILLE     92  69  91  67 /  50  30  40  20
MACON           97  67  95  69 /  30  10  40  30
ROME            97  66  93  65 /  50  30  40  20
PEACHTREE CITY  94  64  93  65 /  50  20  40  30
VIDALIA         94  71  98  73 /  10  10  30  30

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

17

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
1039 AM EDT SAT JUN 11 2011

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-121445-
BALDWIN-BANKS-BARROW-BARTOW-BIBB-BLECKLEY-BUTTS-CARROLL-CATOOSA-
CHATTAHOOCHEE-CHATTOOGA-CHEROKEE-CLARKE-CLAYTON-COBB-COWETA-
CRAWFORD-CRISP-DADE-DAWSON-DEKALB-DODGE-DOOLY-DOUGLAS-EMANUEL-
FANNIN-FAYETTE-FLOYD-FORSYTH-GILMER-GLASCOCK-GORDON-GREENE-
GWINNETT-HALL-HANCOCK-HARALSON-HARRIS-HEARD-HENRY-HOUSTON-JACKSON-
JASPER-JEFFERSON-JOHNSON-JONES-LAMAR-LAURENS-LUMPKIN-MACON-
MADISON-MARION-MERIWETHER-MONROE-MONTGOMERY-MORGAN-MURRAY-
MUSCOGEE-NEWTON-NORTH FULTON-OCONEE-OGLETHORPE-PAULDING-PEACH-
PICKENS-PIKE-POLK-PULASKI-PUTNAM-ROCKDALE-SCHLEY-SOUTH FULTON-
SPALDING-STEWART-SUMTER-TALBOT-TALIAFERRO-TAYLOR-TELFAIR-TOOMBS-
TOWNS-TREUTLEN-TROUP-TWIGGS-UNION-UPSON-WALKER-WALTON-WARREN-
WASHINGTON-WEBSTER-WHEELER-WHITE-WHITFIELD-WILCOX-WILKES-
WILKINSON-
1039 AM EDT SAT JUN 11 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH AND CENTRAL GEORGIA.

.DAY ONE...THIS AFTERNOON AND TONIGHT
SCATTERED THUNDERSTORMS EXPECTED ACROSS PORTIONS OF NORTH AND
CENTRAL GEORGIA THIS AFTERNOON AND TONIGHT. A FEW SEVERE
THUNDERSTORMS CAN BE EXPECTED ACROSS NORTH GEORGIA.

.SYNOPSIS...
A WEAK SURFACE TROUGH LINGERED ACROSS NORTH GEORGIA.
MEANWHILE...WEAK HIGH PRESSURE ALOFT REMAINED OVER THE AREA
BETWEEN A LOW PRESSURE TROUGH LOCATED ACROSS THE EASTERN GULF AND
A SERIES OF WEAK DISTURBANCES MOVING ACROSS THE OHIO AND TENNESSEE
VALLEY REGION.

.PRIMARY HAZARDS...
THE PRIMARY HAZARD FROM THUNDERSTORMS THIS AFTERNOON AND TONIGHT
WILL BE FREQUENT CLOUD-TO-GROUND LIGHTNING. ISOLATED STRONG TO
SEVERE THUNDERSTORMS WILL BE POSSIBLE...PRODUCING STRONG WIND GUSTS AND
QUARTER-SIZED HAIL. HEAVY RAIN CAN ALSO BE EXPECTED WITH THE SLOW
MOVING OR NEARLY STATIONARY STORMS. THUNDERSTORMS ARE EXPECTED TO
BE MOST NUMEROUS NORTHWEST OF A COLUMBUS...TO MACON...TO WARRENTON
LINE BETWEEN 2 PM AND MIDNIGHT EDT.

.DISCUSSION...
A WEAK AND DIFFUSE UPPER-LEVEL PATTERN REMAINED IN PLACE ACROSS
THE REGION AS THE AREA REMAINS UNDER THE INFLUENCE OF HIGH
PRESSURE ALOFT. HIGH TEMPERATURES ONCE AGAIN IN THE 90S WITH DEWPOINTS
IN THE MID 60S WILL LEAD TO A MODERATELY UNSTABLE ATMOSPHERE BY
AFTERNOON...WITH AFTERNOON CAPES IN THE 2000-3000 RANGE ACROSS NORTH
GEORGIA. A SLIGHTLY MORE STABLE ATMOSPHERE WILL BE PRESENT ACROSS
PORTIONS OF EAST CENTRAL GEORGIA. A WEAK SURFACE TROUGH LINGERING
ACROSS NORTH GEORGIA WILL BE THE FOCUS FOR THUNDERSTORM
DEVELOPMENT BY AFTERNOON. THUNDERSTORM OUTFLOW BOUNDARIES AND A
SEA-BREEZE MOVING NORTHWEST FROM SOUTHEAST GEORGIA...ALONG WITH
THE AMBIENT HOT AIR MASS...WILL ALLOW FOR THUNDERSTORMS TO
CONTINUE WELL INTO THE EVENING SATURDAY AND POTENTIALLY EVEN INTO
THE EARLY MORNING HOURS SUNDAY.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY
THERE IS A CHANCE OF THUNDERSTORMS EACH DAY.

.SPOTTER INFORMATION STATEMENT...
SPOTTERS ACTIVATION IS NOT REQUESTED BUT SPOTTERS ARE ENCOURAGED
TO SUBMIT REPORTS OF SEVERE WEATHER THROUGH THE WEB BY GOING TO
WEATHER.GOV/ATLANTA.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
139 PM EDT SAT JUN 11 2011

GAZ033-044-053>055-111815-
139 PM EDT SAT JUN 11 2011

...SIGNIFICANT WEATHER ADVISORY FOR PEA SIZED HAIL AND 35 MPH WINDS
IN COWETA...FAYETTE...CLAYTON AND FULTON COUNTIES UNTIL 215 PM EDT...

AT 133 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
SCATTERED STRONG THUNDERSTORMS FROM SANDTOWN TO RIVERDALE. MOVEMENT
WAS A SLOW DRIFT TO THE SOUTH.

THESE STORMS HAVE THE POTENTIAL TO PRODUCE PEA SIZED HAIL...FREQUENT
CLOUD TO GROUND LIGHTNING AND WIND GUSTS TO 35 MPH AS THEY MOVE
ACROSS NORTHEAST COWETA...NORTH FAYETTE...CLAYTON AND SOUTH FULTON
COUNTIES THROUGH 215 PM EDT. BRIEF HEAVY DOWNPOURS WILL CAUSE
PONDING OF WATER ON ROADWAYS.

&&

LAT...LON 3373 8459 3378 8452 3375 8441 3359 8433
      3339 8437 3339 8456 3341 8480
TIME...MOT...LOC 1738Z 038DEG 2KT 3376 8454 3368 8448
          3359 8440