Special Weather Statement, NWS Atlanta, GA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
201 PM EDT MON OCT 1 2012

.PREV DISCUSSION...

UPDATE...
/ISSUED 1120 AM EDT MON OCT 1 2012/
OVERALL NOT MUCH IN TERMS OF CHANGES TO THE FORECAST FOR TODAY AS
THE GRIDS ALREADY REFLECT HIGH RAIN CHANCES AND INCREASING THUNDER
CHANCES THROUGH THE AFTERNOON.

MODIFIED 12Z FFC SOUNDING SHOWS AROUND 2000 J/KG OF CAPE EXPECTED
THIS AFTERNOON WITH 0 TO 3KM SRH AROUND 311. STILL EXPECT AN
ATMOSPHERE TODAY CAPABLE OF PRODUCING ISOLATED TORNADOES AND
DAMAGING WIND WITH THE BEST CHANCES DURING THE AFTERNOON AND
EVENING HOURS. CLOUD COVERAGE HAS HELPED TO KEEP THUNDER AT BAY
THIS MORNING. STRONGER EMBEDDED CONVECTION IS EXPECTED TO DEVELOP
IN THE AREA OF SHOWERS OVER WEST GEORGIA AS IT SHIFTS EASTWARD
THROUGH THE AFTERNOON SO WILL CONTINUE TO HAVE TO WATCH THIS AREA
FOR ROTATION. BEHIND THIS AREA WHERE CLOUDS ARE ALREADY
SCATTERING /OVER ALABAMA/...ADDITIONAL DEVELOPMENT IS POSSIBLE
BRINGING ANOTHER THREAT OF STRONG TO SEVERE STORMS.

OVER THE PAST 24 HOURS...HAVE SEEN AROUND 1 INCH OF RAIN ACROSS
NORTH GEORGIA WITH ISOLATED HIGHER AMOUNTS NEAR 2 INCHES. ACROSS
CENTRAL GEORGIA HAVE SEEN MAINLY LESS THAN 1 INCH. COULD SEE
ANOTHER INCH...MAINLY ACROSS NORTH GEORGIA DURING THE REMAINDER OF
THE EVENT. AT THIS POINT...NO HYDRO CONCERNS.

11

SHORT TERM /TODAY THROUGH TUESDAY/...
/ISSUED 303 AM EDT MON OCT 1 2012/
MODEL TRENDS REMAIN CONSISTENT WITH PREVIOUS RUNS AND
GFS/NAM/ECMWF REMAIN SIMILAR IN THE LARGE SCALE EVOLUTION OF THE
SYSTEM DEVELOPING IN THE LOWER MISSISSIPPI VALLEY. MODELS STILL
SHOW A STRONG BLOCKING RIDGE DEVELOPING OFF THE MID AND SOUTHERN
ATLANTIC COAST. UPPER LOW AND ASSOCIATED SURFACE LOW SLOWLY LIFT
NORTH FROM THE LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY
AND EVENTUALLY THE OHIO VALLEY THROUGH THE PERIOD. STRONG
SOUTHWESTERLY...DIFFLUENT UPPER FLOW INCREASES ACROSS THE FORECAST
AREA TODAY WITH A STRENGTHENING UPPER-LEVEL JET DEVELOPING FROM
THE LOWER MISSISSIPPI VALLEY INTO THE GREAT LAKES. THE SURFACE LOW
IS FORECAST TO LIFT NORTH TRYING TO DRAG THE STATIONARY FRONT
CURRENTLY ACROSS CENTRAL GEORGIA BACK NORTH AS A WARM FRONT DURING
THE DAY TODAY...HOWEVER ALL THREE MODELS ARE INDICATING THE RIDGE
IN THE LEE OF THE APPALACHIANS WILL STUBBORNLY HOLD ON THROUGH
MUCH OF THE DAY ACROSS NORTH GEORGIA. WEAK TO MODERATE INSTABILITY
AND MODERATE TO STRONG SHEAR SPREAD INTO THE STATE DURING THE DAY
WITH INCREASING CHANCES FOR THUNDERSTORMS. THE POTENTIAL FOR
SEVERE THUNDERSTORMS...MAINLY DAMAGING WINDS AND POSSIBLY AN
ISOLATED TORNADO...EXISTS ACROSS THE FORECAST AREA
TODAY...ESPECIALLY IN THE WESTERN AND SOUTHERN PORTIONS OF THE
AREA. THE HOW FAR THIS THREAT EXTENDS NORTH AND EAST INTO THE
FORECAST AREA WILL GREATLY DEPEND ON HOW FAR NORTH AND EAST THE
WARM FRONT LIFTS. COLD FRONTAL BOUNDARY ASSOCIATED WITH THE
SURFACE LOW PUSHES INTO THE WESTERN PORTION OF THE STATE BY LATE
AFTERNOON OR EARLY EVENING AND PROGRESSES SLOWLY ACROSS THE
FORECAST AREA TONIGHT. INSTABILITY IS MINIMIZED SOMEWHAT DURING
THE OVERNIGHT PERIOD BUT ISOLATED TO SCATTERED THUNDERSTORMS ARE
STILL EXPECTED. BEST CHANCES FOR PRECIPITATION SHOULD BE EXITING
TO THE EAST BY EARLY TUESDAY...BUT WITH THE UPPER TROUGH AXIS HUNG
UP TO THE WEST OF THE STATE...CHANCES FOR SHOWERS AND A FEW
THUNDERSTORMS LINGER ACROSS MAINLY THE EASTERN HALF OF NORTH AND
CENTRAL GEORGIA.

20

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
/ISSUED 303 AM EDT MON OCT 1 2012/
THE DEEP TROUGH TO THE WEST OF THE CWA WEAKENS AND FILLS WITH THE
MAIN AREA OF ENERGY GOING NORTH OF THE STATE. THIS LEAVES US IN A
SOUTHWEST FLOW THAT BECOMES WEST BY THE END OF THE WEEK WITH THE
MAIN WESTERLIES TO OUR NORTH. ACCORDING TO THE GFS THE WESTERLIES
SINK INTO THE SOUTH WHILE THE ECMWF KEEP THE WESTERLIES OVER THE
OHIO VALLEY. THE GFS SOLUTION WOULD BRING LOW CHANCE POPS INTO THE
CWA FOR THE WEEKEND WHILE THE ECMWF WOULD KEEP US DRY. FOR AT LEAST
THE FIRST PART OF THE LONG TERM WE SHOULD SEE A DRYING TREND
ALTHOUGH WITH A SOUTHWEST FLOW THERE SHOULD BE AMPLE CLOUDS. FOR THE
WEEKEND WILL LEAN TOWARD THE GFS SOLUTION AND GO WITH LOW CHANCE
POPS...MAINLY FOR NORTH GA. AM CONCERNED ABOUT THE LOW TEMPS FOR THE
FIRST PART OF THE LONG TERM. FEEL WITH CLOUDS AND A SOUTHWEST FLOW
IT WILL BE HARD TO SEE LOWS IN THE 40S/50S AND WILL RAISE MIN TEMPS
A FEW DEGREES...ESPECIALLY ON WED AND THU MORNING. REST OF THE TEMPS
LOOK GOOD.

17

HYDROLOGY...
/ISSUED 303 AM EDT MON OCT 1 2012/
THE MAJORITY OF THE FORECAST AREA WILL CONTINUE TO EXPERIENCE
WIDESPREAD...BENEFICIAL PRECIPITATION THROUGH TUESDAY. CURRENT
STORM-TOTAL PRECIPITATION FORECASTS CONTINUE TO BE BELOW 3-6 HOUR
FLASH FLOOD GUIDANCE AND NO WIDESPREAD FLOODING ISSUES ARE EXPECTED
AT THIS TIME.

&&

.AVIATION...
18Z UPDATE...
MAINLY IFR TO MVFR CONDITIONS ACROSS THE AREA THIS AFTERNOON AND
EXPECT TREND TO CONTINUE. ONE OF MAIN CHALLENGES IS CHANCE OF TS.
GREATER CHANCES ARE ACROSS MCN AND CSG AREA BUT THREAT DOES STILL
EXIST TO THE NORTH. EVEN WITH HEAVY SHRA ACROSS ATL SITES NOW...
THINK THE BIGGER THREAT OF TS IS WITH ISOLATED CELLS DEVELOPING
WEST OF THIS LINE. OVERNIGHT WILL SEE VLIFR TO LIFR CIGS AND VSBYS
AGAIN ACROSS THE SITES AND SOMEWHAT CONCERNED WE ARE ON THE
OPTIMISTIC SIDE OF VSBY/CIGS AT ATL. WINDS WILL BE A CHALLENGE TUESDAY
MORNING AND HOVER AROUND SOUTH AROUND SUNRISE AND THEN BECOME SW
DURING THE LATE MORNING TO AFTERNOON TIME FRAME.

//ATL CONFIDENCE...18Z UPDATE...
MEDIUM CONFIDENCE ON CIGS AND VSBYS. LOW CONFIDENCE ON TS TIMING.
HIGH CONFIDENCE ON WIND...BUT LOW AFTER 09Z TUESDAY DUE TO WIND
SHIFT FROM SE TO SW.

11

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          73  66  77  56 / 100  80  40  10
ATLANTA         75  65  75  57 / 100  70  10  10
BLAIRSVILLE     68  61  73  51 / 100  80  40  10
CARTERSVILLE    74  63  75  55 / 100  70  10  10
COLUMBUS        80  67  79  58 / 100  50   5   5
GAINESVILLE     71  64  75  57 / 100  80  30  10
MACON           81  67  82  57 /  90  70  20  10
ROME            74  63  75  55 / 100  60  10  10
PEACHTREE CITY  76  65  76  52 / 100  70  10  10
VIDALIA         87  71  84  65 /  50  40  40  10

&&

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

UPDATE...11
SHORT TERM...20
LONG TERM....41
AVIATION...11

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
249 PM EDT MON OCT 1 2012

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-020830-
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-
249 PM EDT MON OCT 1 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH AND CENTRAL GEORGIA.

.DAY ONE...THIS AFTERNOON AND TONIGHT...
ISOLATED SEVERE STORMS STILL POSSIBLE THIS AFTERNOON AND TONIGHT
ACROSS NORTH AND CENTRAL GEORGIA.

.SYNOPSIS...
AN AREA OF LOW PRESSURE OVER WEST CENTRAL ALABAMA WILL MOVE
NORTHEAST AND PULL A WARM FRONT...CURRENTLY ACROSS CENTRAL
GEORGIA...NORTHWARD INTO NORTH GEORGIA THIS AFTERNOON AND EVENING.
THIS WILL KEEP WIDESPREAD SHOWERS AND ISOLATED THUNDERSTORMS OVER
THE REGION THROUGH TONIGHT. A FEW STORMS COULD BECOME SEVERE THIS
AFTERNOON AND EVENING.

.PRIMARY HAZARDS...
THE PRIMARY HAZARDS FROM THE SEVERE STORMS WILL BE ISOLATED
TORNADOES AND DAMAGING WINDS. LARGE HAIL MAY BE POSSIBLE LATER THIS
EVENING OVER NORTH GEORGIA. THE MORE FAVORABLE TIME FOR SEVERE STORM
DEVELOPMENT WILL BE FROM MID AFTERNOON THROUGH LATE THIS EVENING...
HOWEVER A FEW STRONG STORMS COULD LINGER AFTER MIDNIGHT.

.DISCUSSION...
THE STRONG UPPER TROUGH TO THE WEST WILL CONTINUE TO FEED WARM MOIST
AIR FROM THE GULF INTO THE REGION. DAYTIME HEATING HAS INCREASED
CAPES INTO THE 1500 TO 2000 J/KG RANGE ACROSS CENTRAL AND PARTS OF
NORTH GEORGIA THIS AFTERNOON. THIS COUPLED WITH STRONG LOW LEVEL
SHEAR WILL ALLOW FOR A FEW STORMS TO BECOME SEVERE. THE MAIN THREAT
WILL BE ACROSS THE WESTERN HALF OF THE STATE FROM MID AFTERNOON...
THROUGH THE EVENING HOURS. THE SEVERE WEATHER THREAT SHOULD GREATLY
DIMINISH AFTER MIDNIGHT TONIGHT.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY...
ISOLATED THUNDERSTORMS ARE POSSIBLE ACROSS THE EASTERN PARTS OF
THE REGION ON TUESDAY. HAZARDOUS WEATHER IS NOT EXPECTED WEDNESDAY
THROUGH SUNDAY.

.SPOTTER INFORMATION STATEMENT...
SPOTTERS SHOULD MONITOR THE LATEST INFORMATION...ESPECIALLY THIS
AFTERNOON AND TONIGHT FOR POSSIBLE ACTIVATION ACROSS.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
259 PM EDT MON OCT 1 2012

GAZ034-045>048-056>058-068>070-011945-
259 PM EDT MON OCT 1 2012

...SIGNIFICANT WEATHER ADVISORY FOR HEAVY RAIN IN WALTON...
SPALDING...ROCKDALE...PIKE...NEWTON...LAMAR...UPSON...BUTTS...
DEKALB...GWINNETT AND HENRY COUNTIES UNTIL 345 PM EDT...

AT 253 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
LINE OF HEAVY RAINFALL FROM ROSEBUD TO HANNAHS MILL...MOVING NORTHEAST AT 20
MPH.

RAINFALL AMOUNTS BETWEEN 1 AND 2 INCHES CAN BE EXPECTED ACROSS
WALTON...SPALDING...ROCKDALE...PIKE...NEWTON...LAMAR...UPSON...BUTTS.
..DEKALB...GWINNETT AND HENRY COUNTIES...INCLUDING AREAS AROUND
CENTERVILLE...KLONDIKE...HANNAHS
MILL...MEANSVILLE...WILLIAMSON...ZEBULON...EXPERIMENT...HIGHLAND
MILLS...TOWALAGA...ROVER...SUNNY SIDE...GRIFFIN...PANOLA MOUNTAIN
STATE PARK...RICHARDSON PARK AND LAKEVIEW ESTATES. DRIVERS SHOULD
USE CAUTION AS INTENSE RAINFALL WILL REDUCE VISIBILITIES. PONDING OF
WATER ON ROADWAYS IS ALSO LIKELY.

&&

LAT...LON 3390 8378 3367 8386 3355 8389 3338 8405
      3307 8414 3292 8436 3321 8438 3390 8404
TIME...MOT...LOC 1857Z 228DEG 17KT 3383 8393 3321 8424
          3299 8433

KS