Special Weather Statement, NWS Atlanta, GA

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

.PREV DISCUSSION... /ISSUED 1048 AM EDT FRI AUG 17 2012/

UPDATE...
DIFFICULT FORECAST FOR TODAY...WITH LITTLE FORECAST AGREEMENT WITH
THE SHORT TERM MODELS. OVERNIGHT MCS PUSHED INTO AL...WITH LARGE
AREA OF RAIN SHOWERS REMAINING ACROSS THE SOUTHERN HALF OF THE
STATE. THIS COMPLEX USHERED DECENT CLOUD COVER ACROSS THE FAR
WESTERN SIDE OF GA THIS MORNING...KEEPING A MORE STABILIZED
ENVIRONMENT OVER THAT AREA. CLOUDS ALREADY BEGINNING TO DIMINISH
THIS MORNING...BUT AS A RESULT OF THESE NOT WELL FORECAST
CLOUDS...MODELS HAVING DIFFICULTLY FINDING AN AGREEMENT ON
AFTERNOON ACTIVITY AS FRONTAL BOUNDARY APPROACHES THE REGION AND
STRONG UPPER LEVEL DISTURBANCE DROPS INTO THE STATE JUST AHEAD OF
IT. LOCAL WRF INDICATING A BUSY CONVECTIVE AFTERNOON FOR THE
STATE...WITH ISOLATED CELLS BECOMING MORE ORGANIZED AND LINEAR IN
NATURE BY LATE AFTERNOON AND EARLY EVENING AS THEY PUSH THROUGH
THE METRO AREA. BY CONTRAST...OTHER MODELS...SUCH AS THE
HRRR...KEEP MUCH OF THE ACTIVITY OVER FAR NORTH GEORGIA OR THE FAR
SE PORTIONS OF THE STATE...LEAVING THE METRO AREA LARGELY UNSCATHED.

FOR NOW...HAVE LEANED MORE TOWARDS THE THINKING OF SPC...WITH
ISOLATED STORMS EXPECTED THROUGH THE AFTERNOON AND INTO TONIGHT. THIS
THINKING IS MORE PARALLEL WITH THE LOCAL WRF SOLUTION. COULD SEE
SOME CONVECTIVE INITIATION AS EARLY AS 12-1PM...BUT EXPECTING
ACTIVITY TO REALLY FIRE 2-3PM AND AFTER.

AGAIN...THIS IS A DIFFICULT FORECAST...AND UPDATES WILL LIKELY BE
NECESSARY THROUGH THE DAY.

31

PREV DISCUSSION... /ISSUED 735 AM EDT FRI AUG 17 2012/

SHORT TERM /TODAY THROUGH SATURDAY/...
/ISSUED AT 401 AM EDT FRI AUG 17 2012/
THE CONVECTIVE REMNANTS OF AN MCS IS PUSHING ACROSS NORTH AL AND NW
GA EARLY THIS MORNING. EXPECT CURRENT WEAKENING TREND TO CONTINUE...
SPREADING MAINLY MID LEVEL CLOUDINESS AND SPOTTY LIGHT RAIN INTO THE
ATLANTA METRO AREA BY MID TO LATE MORNING. ALTHO CANNOT RULE OUT A
FEW RUMBLES OF THUNDER THIS MORNING... EXPECT SPOTTY LIGHT RAIN TO
BE THE MAIN PRECIP TYPE IN ATLANTA THIS MORNING.

THE GREATER CONCERN IS AN APPROACHING COLD FRONT THAT IS EXPECTED
TO PUSH INTO NORTH GEORGIA LATER THIS AFTERNOON. GFS AND NAM SHOW
A SERIES OF STRONG UPPER VORT MAXES TRAVERSING NORTH GEORGIA
DURING DAYTIME HEATING. THIS COUPLED WITH THE FRONT SHOULD RESULT
IN WIDESPREAD SHOWERS AND THUNDERSTORMS PUSHING INTO NORTH GEORGIA
TODAY...WITH SCATTERED CONVECTION POSSIBLY SPREADING INTO PARTS
OF CENTRAL GEORGIA AS WELL. RESIDUAL CLOUD COVER FROM THIS
MORNINGS DISSIPATING MCS SHOULD HELP HOLD TEMPERATURES AND
INSTABILITIES DOWN A BIT TODAY. HOWEVER...TIMING OF THE UPPER
VORT MAX DURING MAX HEATING...ALONG WITH FRONTAL FORCING...ALL
SUGGEST THE POTENTIAL FOR ISOLATED STRONG TO SEVERE STORMS ACROSS
PARTS OF NORTH GEORGIA LATER THIS AFTERNOON AND EARLY EVENING. SPC
CONTINUES TO PLACE MUCH OF NORTH GEORGIA IN A SLIGHT RISK AREA
TODAY...GENERALLY ALONG AND NORTH OF A LAGRANGE TO COVINGTON TO
ATHENS LINE. THE MAIN STORM THREATS WILL BE DAMAGING WIND AND
MARGINAL SIZED HAIL. LOCALLY HEAVY RAIN IS ALSO A CONCERN WITH
TRAINING CELLS AHEAD OF THE FRONT. THE UPPER DISTURBANCES PUSH
EAST BY MIDNIGHT...SO EXPECT THE ASSOCIATED CONVECTION AHEAD OF
THE FRONT TO GREATLY DIMINISH BY THEN...ESPECIALLY WITH LOSS OF
DAYTIME HEATING.

THE FRONT STALLS ACROSS CENTRAL GEORGIA ON SATURDAY...SO WILL
SHOW THE GREATER RAIN CHANCES THERE SATURDAY AFTERNOON. MARGINAL
INSTABILITIES AND LACK OF UPPER SUPPORT SHOULD HELP HOLD STORM
DEVELOPMENT BELOW SEVERE LIMITS ON SATURDAY.

OTHERWISE...STARTED WITH A MAV AND MET BLEND FOR TEMPS THROUGH THE
SHORT TERM...THEN LEANED TOWARD THE COOLER MET HIGHS FOR TODAY
WITH RESIDUAL CLOUDINESS...THEN WARMER MAV HIGHS ON SATURDAY WITH
LESS CLOUDS AND ONLY ISOLATED TO SCATTERED CONVECTION EXPECTED.

39

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          87  69  89  67 /  80  40  30  20
ATLANTA         86  70  86  69 /  80  40  30  20
BLAIRSVILLE     80  66  81  62 /  80  50  20  10
CARTERSVILLE    86  69  85  64 /  90  50  20  20
COLUMBUS        91  72  89  70 /  80  40  30  20
GAINESVILLE     86  70  86  67 /  80  50  30  20
MACON           92  71  91  71 /  80  30  40  30
ROME            87  69  88  63 /  90  50  20  10
PEACHTREE CITY  87  69  86  66 /  80  40  30  20
VIDALIA         93  73  91  73 /  50  30  40  30

&&

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

SHORT TERM...31
LONG TERM....BAKER
AVIATION...31

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
1018 AM EDT FRI AUG 17 2012

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-181430-
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-
1018 AM EDT FRI AUG 17 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH AND CENTRAL GEORGIA.

.DAY ONE...TODAY AND TONIGHT...
ISOLATED SEVERE THUNDERSTORMS EXPECTED ACROSS THE NORTH AND WEST
CENTRAL PORTIONS OF GEORGIA 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 WEST AND NORTH OF
A LINE FROM AMERICUS TO MACON TO LEXINGTON DURING THIS AFTERNOON
AND EVENING. ALTHOUGH SEVERE STORMS ARE NOT EXPECTED ACROSS THE
SOUTHEASTERN PORTION OF CENTRAL GEORGIA 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