Special Weather Statement, NWS Atlanta, GA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
336 PM EDT FRI AUG 17 2012

.SHORT TERM /TODAY THROUGH SUNDAY NIGHT/...
MODEL RELIABILITY FOR THIS AFTERNOON BECOMING MORE APPARENT AS
CONVECTION INITIATES ACROSS THE AREA. 12Z NCEP WRF NMM HAS HAD THE
BEST HANDLE ON THE LINE OF CONVECTION EXTENDING JUST NE OF COLUMBUS
TO JUST SOUTH OF ATHENS. CLOUD SHIELD PRESENT ACROSS MUCH OF NORTH
GEORGIA AS A RESULT OF OVERNIGHT MCS IN AL HAS PREVENTED SIGNIFICANT
DESTABILIZATION OF THE ATMOSPHERE IN THAT AREA. HIGH UNCERTAINTY IN
THE FORECAST STILL REMAINS FOR THE EVENING AND OVERNIGHT HOURS...AS
UPPER LEVEL POSITIVE VORTICITY AREA MOVES INTO NORTH GEORGIA...
FOLLOWED BY THE FRONTAL BOUNDARY. IF THE NORTH GA CLOUD SHIELD IS
ABLE TO SCATTER...THE COMBINATION OF THESE FEATURES AS THEY MOVE
INTO THE CWA COULD SUPPORT THUNDERSTORM DEVELOPMENT. FOR NOW...HAVE
KEPT AFTERNOON POPS THE HIGHEST IN THE SOUTHERN HALF OF THE
CWA...DIMINISHING THEM FROM LIKELY TO GOOD CHANCE INTO THE OVERNIGHT
HOURS. HAVE OPTED TO GO WITH GOOD CHANCE POPS ACROSS NORTH GA
THROUGH THE OVERNIGHT HOURS TO ACCOUNT FOR ANY ACTIVITY THAT MAY
ACCOMPANY THE FRONT ON THE WAY IN.

COLD FRONT...POSITIONED BACK IN CENTRAL TENNESSEE...IS EXPECTED TO
PUSH INTO CENTRAL GEORGIA BY SATURDAY MORNING...AND ANY ACTIVITY
SATURDAY AFTERNOON SHOULD BE FOCUSED ALONG OR SOUTH OF THIS
BOUNDARY. HAVE VIRTUALLY NO POPS FAR NORTH...WITH SLIGHT CHANCE
THROUGH THE ATL METRO AND AHN AREAS...AND THEN GOOD CHANCE IN THE
SOUTHERN THIRD OF THE CWA. MARGINAL INSTABILITIES AND LIMITED
SUPPORT SHOULD KEEP DEVELOPING THUNDERSTORMS BELOW SEVERE CRITERIA.

FRONT MAKES LITTLE FORWARD PROGRESS INTO SUNDAY...AND WITH
DEVELOPMENT OF LOCALIZED LOW PRESSURE AREAS ALONG THE
BOUNDARY...COMBINED WITH A SERIES OF UPPER LEVEL IMPULSES MOVING
INTO THE AREA FROM THE NORTHERN GULF IN THE LONGWAVE FLOW. THIS WILL
KEEP SLIGHT CHANCE TO GOOD CHANCE POPS ACROSS THE AREA THROUGH THE
REMAINDER OF THE SHORT TERM.

AS FOR TEMPERATURES...HAVE TAKEN A BLEND OF THE MODEL GUIDANCE.
DRIER DEWPOINTS MOVE INTO NORTH GEORGIA BEHIND THE BOUNDARY...WITH
COOLER TEMPERATURES IN STORE. AHEAD OF THE FRONT...MOIST AND WARMER
CONDITIONS REMAIN IN PLACE...THOUGH PRECIP ACTIVITY AND CLOUD COVER
WILL KEEP TEMPERATURES SLIGHTLY MORE MILD. OVERALL...HIGHS IN THE
80S...WITH LOWS IN THE LOW 60S NORTH AND LOW 70S SOUTH BY SUNDAY.

31

&&

.LONG TERM /MONDAY THROUGH FRIDAY/... LATEST GFS SOLUTION BEGINS TO
DIVERGE FROM THE ECMWF FROM TUESDAY INTO THURSDAY AS IT HOLDS ONTO
AN UPPER SHORTWAVE TROUGH WITH STRONG MOISTURE ADVECTION FROM THE
SOUTHWEST ALONG WITH THE INFLUENCE OF A WEAK SFC LOW TRACKING NEWD
FROM THE GULF COAST WEDNESDAY INTO THURSDAY. ON THE OTHER
HAND...THE ECMWF DEVELOPS AN UPPER CLOSED LOW NW OF THE AREA AND
HAS MUCH LESS MOISTURE ADVECTION AND NO COASTAL SFC LOW. DESPITE
SUCH DISCREPANCIES THE BEST AVAILABLE MOISTURE LOOKS TO BE IN THE
SOUTHEAST PORTION OF THE AREA SO WILL KEEP CURRENT POPS AS
FORECAST WITH CHANCE SOUTH TO SLIGHT CHANCE ELSEWHERE. FUTURE
MODEL RUNS WILL BE MONITORED TO SEE IF CURRENT UNCERTAINTY
IMPROVES. BOTH GFS AND ECMWF FCST DAILY MAX TEMPS LOOK TO BE
RATHER COOL SO HAVE BUMPED VALUES DOWN SEVERAL DEGREES MONDAY
THROUGH WEDNESDAY. MADE NO OTHER CHANGES TO FORECAST. PREVIOUS
DISCUSSION FOLLOWS...

03

LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
/ISSUED AT 401 AM EDT FRI AUG 17 2012/
CWA REMAINS IN LONGWAVE TROUGH AT THE BEGINNING OF THE LONG TERM.
MEANWHILE AT THE SFC...FRONT THAT MOVES THROUGH IN THE SHORT TERM
REMAINS SITUATED ACROSS THE SOUTHERN HALF OF THE STATE. THIS
PATTERN WILL DOMINATE THE LONG TERM. WITH FRONT MEANDERING AROUND
CENTRAL GEORGIA...BEST CHANCES OF RAIN THROUGH THE LONG TERM WILL
REMAIN ACROSS THE SOUTHERN HALF OF THE CWA. IN ADDITION WILL SEE
WEAK DISTURBANCES MOVE ALONG THE FRONT AS IT REMAINS STATIONARY.
GFS SHOWS THE BEST VORT MAX TO MOVE ALONG THE FRONT ON MONDAY AND
THIS WILL HELP TO REINFORCE CHANCE OF POPS. INITIALLY OVER THE
WEEKEND...POPS ARE ON THE LOWER SIDE OF GUIDANCE AS IT APPEARS MAV
IS OVER DOING POPS...WHEREAS LATER IN THE LONG TERM...POPS ARE
CLOSER TO GUIDANCE.

11

&&

.AVIATION...
18Z UPDATE...
AFTERNOON CONVECTION HAS STARTED FIRING SOUTH OF THE ATL TO AHN
SITES...AND EXPECT BULK OF ACTIVITY TO STAY IN THIS AREA INTO THE
EVENING HOURS. FOR NOW...HAVE GENERALLY 19-23Z TEMPO TS AT ALL
SITES...BUT WILL NEED TO TAILOR THIS AS AFTERNOON ACTIVITY
CONTINUES. AS FRONTAL BOUNDARY APPROACHES TONIGHT...POSSIBLE
SHOWERS AND ISOLATED CONVECTION WILL MOVE INTO NORTH GA. IMPACT TO
ATL METRO SITES IS UNCERTAIN...AND HAVE LEFT IT OUT OF THE TAF FOR
NOW. RESTRICTED MORNING VSBYS AND CIGS DEPENDENT ON PRECIP
ACTIVITY TODAY...AND COULD SEE SCT-BKN IFR CIGS. IN
GENERAL...WINDS SHOULD STAY N OF W...EXCEPT VRB IN AND NEAR
STORMS. SATURDAY STORMS SHOULD BE ALONG OR SOUTH OF CSG TO MCN
AFTER 18Z.

//ATL CONFIDENCE...18Z UPDATE...
HIGH CONFIDENCE ON WINDS...MEDIUM ON EVERYTHING ELSE.

31

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          67  88  68  87 /  30  20  20  30
ATLANTA         69  86  70  86 /  40  20  20  40
BLAIRSVILLE     63  82  59  81 /  40  20  10  20
CARTERSVILLE    67  85  64  86 /  40  20  20  30
COLUMBUS        71  89  72  88 /  50  30  40  50
GAINESVILLE     68  85  67  84 /  30  20  20  30
MACON           70  91  71  88 /  50  30  30  50
ROME            67  87  63  87 /  40  20  20  30
PEACHTREE CITY  68  87  67  86 /  30  20  20  40
VIDALIA         74  92  74  90 /  60  30  30  50

&&

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

SHORT TERM...31
LONG TERM....11/03
AVIATION...31

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
320 PM EDT FRI AUG 17 2012

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-181930-
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-
320 PM EDT FRI AUG 17 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH AND CENTRAL GEORGIA.

.DAY ONE...THIS AFTERNOON AND TONIGHT...
ISOLATED SEVERE THUNDERSTORMS EXPECTED ACROSS SOUTHEAST CENTRAL
GEORGIA AND POSSIBLE ELSEWHERE THIS AFTERNOON AND TONIGHT.

.SYNOPSIS...
A FRONT SITUATED ACROSS THE MIDWEST WILL SINK INTO GEORGIA THIS
AFTERNOON.

.PRIMARY HAZARDS...
THE PRIMARY HAZARD ASSOCIATED WITH ANY SEVERE STORM WILL BE
DAMAGING WIND. IN ADDITION...FREQUENT LIGHTNING...QUARTER SIZED
HAIL AND HEAVY RAIN WILL BE POSSIBLE.

.DISCUSSION...
A COLD FRONT WILL PUSH INTO GEORGIA THIS AFTERNOON. THIS FEATURE
IN ADDITION TO DAYTIME HEATING AND AN UPPER LEVEL DISTURBANCE
MOVING THROUGH THE AREA WILL ALLOW FOR SHOWERS AND THUNDERSTORMS
TO DEVELOP. WITH THE FORCING FROM THE FRONT...IN ADDITION TO CAPE
VALUES AROUND 2000 J/KG THIS AFTERNOON...SOME STORMS MAY BECOME
SEVERE. THE BEST CHANCE FOR THIS WILL BE MAINLY SOUTH AND EAST
FROM A COLUMBUS TO MACON TO WARRENTON LINE. ALTHOUGH SEVERE STORMS
ARE NOT EXPECTED ACROSS THE REMAINDER OF NORTH AND CENTRAL
GEORGIA...THEY ARE STILL POSSIBLE AND THE THREAT DOES STILL EXIST
FOR SCATTERED THUNDERSTORMS WITH GUSTY WINDS AND FREQUENT
LIGHTNING.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY...
AS THE FRONT STALLS ACROSS CENTRAL GEORGIA THIS WEEKEND AND
MULTIPLE UPPER LEVEL DISTURBANCES MOVE ALONG THE FRONT...THERE
WILL BE A CHANCE OF THUNDERSTORMS EACH DAY. THE CHANCE OF SEVERE
STORMS SHOULD DECREASE FOR SATURDAY AS SUPPORT FROM THE UPPER LEVEL
FEATURE MOVES OUT OF THE AREA.

.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
132 PM EDT FRI AUG 17 2012

GAZ057-058-171800-
132 PM EDT FRI AUG 17 2012

...SIGNIFICANT WEATHER ADVISORY FOR 40 MPH WINDS IN BUTTS AND HENRY
COUNTIES UNTIL 200 PM EDT...

AT 131 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS FROM OLA TO LUELLA...MOVING EAST AT 10 MPH.

THESE STORMS HAVE THE POTENTIAL TO PRODUCE PEA SIZED HAIL...FREQUENT
CLOUD TO GROUND LIGHTNING AND WIND GUSTS TO 40 MPH AS THEY MOVE
ACROSS BUTTS AND HENRY COUNTIES THROUGH 200 PM EDT. SOME LOCATIONS IN
THE PATH OF THESE STORMS INCLUDE BLACKSVILLE...MCDONOUGH...LUELLA...
OLA...LOCUST GROVE...STARK...MCKIBBEN...WORTHVILLE...FINCHERVILLE AND
JENKINSBURG. HEAVY DOWNPOURS WILL CAUSE PONDING OF WATER ON ROADWAYS.

THESE WIND GUSTS MAY PRODUCE MINOR DAMAGE TO TREE LIMBS AND BLOW
LIGHT...UNSECURED OBJECTS AROUND.

&&

LAT...LON 3350 8407 3347 8394 3342 8391 3337 8386
      3326 8403 3328 8410 3329 8409 3330 8411
      3330 8413 3334 8415 3334 8424 3335 8425
      3336 8433
TIME...MOT...LOC 1732Z 285DEG 10KT 3343 8406 3336 8417

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
248 PM EDT FRI AUG 17 2012

GAZ050-171945-
248 PM EDT FRI AUG 17 2012

...SIGNIFICANT WEATHER ADVISORY FOR HEAVY RAIN IN GREENE COUNTY UNTIL
345 PM EDT...

AT 240 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR ESTIMATED ONE
TO ONE AND A HALF INCHES OF RAIN FROM GRESHAMVILLE TO
PENFIELD...FROM TRAINING THUNDERSTORMS MOVING EAST AT 15 MPH.

RAINFALL AMOUNTS BETWEEN ONE TO TWO INCHES CAN BE EXPECTED ACROSS
GREENE COUNTY...INCLUDING AREAS AROUND PENFIELD...GRESHAMVILLE...
WOODVILLE...GREENSBORO...UNION POINT...AND JACKSONVILLE. DRIVERS
SHOULD USE CAUTION AS INTENSE RAINFALL WILL REDUCE VISIBILITIES.
PONDING OF WATER ON ROADWAYS IS ALSO LIKELY.

&&

LAT...LON 3362 8298 3362 8300 3360 8299 3359 8301
      3349 8298 3336 8316 3339 8319 3338 8322
      3349 8328 3354 8327 3360 8335 3370 8340
      3373 8330 3376 8328 3370 8312 3371 8305
      3369 8299 3367 8295
TIME...MOT...LOC 1844Z 270DEG 12KT 3365 8303 3365 8323

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
634 PM EDT FRI AUG 17 2012

GAZ076-172300-
634 PM EDT FRI AUG 17 2012

...SIGNIFICANT WEATHER ADVISORY FOR PEA SIZED HAIL AND 40 MPH WINDS
IN JEFFERSON COUNTY UNTIL 700 PM EDT...

AT 632 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS FROM 6 MILES EAST OF LOUISVILLE TO WADLEY...
MOVING SOUTHEAST AT 5 MPH.

THESE STORMS HAVE THE POTENTIAL TO PRODUCE PEA SIZED HAIL...FREQUENT
CLOUD TO GROUND LIGHTNING AND WIND GUSTS TO 40 MPH AS THEY MOVE
ACROSS JEFFERSON COUNTY THROUGH 700 PM EDT. SOME LOCATIONS IN THE
PATH OF THESE STORMS INCLUDE MOXLEY...WADLEY...BARTOW AND LOUISVILLE.
HEAVY DOWNPOURS WILL CAUSE PONDING OF WATER ON ROADWAYS.

THESE WIND GUSTS MAY PRODUCE MINOR DAMAGE TO TREE LIMBS AND BLOW
LIGHT...UNSECURED OBJECTS AROUND.

&&

LAT...LON 3286 8229 3281 8237 3281 8241 3280 8242
      3278 8240 3276 8245 3282 8252 3292 8251
      3293 8253 3315 8227 3304 8228 3293 8227
TIME...MOT...LOC 2234Z 327DEG 5KT 3298 8231 3286 8241