Special Weather Statement, NWS Atlanta, GA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
322 PM EDT THU AUG 23 2012

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
LIMITED RAIN CHANCES EXPECTED THROUGH WEEKS END...

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
THE UPPER LEVEL AND SURFACE TROUGH THAT HAS PERSISTED OVER THE
SOUTHEAST THE PAST SEVERAL DAYS WILL SHIFT A BIT TO THE EAST THROUGH
THE SHORT TERM.  THE SHORT TERM MODELS ARE IN GOOD AGREEMENT...AND
CONTINUE TO SHOW ENOUGH MOISTURE OVER THE AREA FOR ISOLATED TO
SCATTERED CONVECTION EACH AFTERNOON.  IN THE VERY SHORT TERM...
THROUGH THIS EVENING ISOLATED SHOWERS HAVE DEVELOPED ALONG AND EAST
OF A CARROLLTON TO HELEN LINE...MOVING TO THE SOUTHWEST.  ANTICIPATE
THIS TREND WILL CONTINUE WITH CELLS DIMINISHING BETWEEN 7-9PM WITH
THE LOSS OF HEATING.  ISOLATED STORMS MAY PROVIDE LOCALLY HEAVY
RAINFALL AND BRIEF WIND GUST TO 35-40MPH.  WITH SIMILAR CONDITIONS
OVER THE AREA FRIDAY AND SATURDAY HAVE TWEAKED POPS AND WEATHER
TOWARD PERSISTENCE.  GUIDANCE TEMPERATURES ARE IN GOOD AGREEMENT AND
AGAIN WILL NOT STRAY TOO FAR.

ATWELL

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
BIG FORECAST STORY THROUGH THE LONG TERM REMAINS TS ISSAC AS IT
MOVES INTO THE GULF OF MEXICO THROUGH THE WEEKEND. TO SEE THE LATEST
OFFICIAL TS ISSAC TRACK FORECAST...PLEASE VISIT NHC.NOAA.GOV.

HIGH PRESSURE RIDGE OVER THE CENTRAL U.S. EXTENDS INTO THE GULF OF
MEXICO THROUGH THE WEEKEND. ISSAC IS EXPECTED TO APPROACH A WEAKNESS
IN THIS RIDGE AS IT MOVES INTO THE GULF OF MEXICO BY LATE WEEKEND.
EXTENDED MODELS HAVE COME INTO BETTER AGREEMENT WITH POSITION OF
ISSAC ENTERING THE NORTHERN GULF OF MEXICO BY TUESDAY MORNING. FOR
NOW...HAVE MADE ADJUSTMENTS TO THE WIND...POP...AND RELATED FIELDS
TO ACCOUNT FOR THE CHANGE IN NHC TRACK FOR THE STORM...AND FOR
CONSISTENCY WITH OUR NEIGHBORS WHO HAVE ALSO MADE SOME CHANGES.

BEYOND THE NHC TRACK PERIOD...MODELS HAVING A LITTLE MORE DIFFICULTY
WITH PROGRESSION OF THE SYSTEM INLAND. ECMWF WANTS TO MOVE THE
SYSTEM NORTHWARD AROUND AREA OF HIGH PRESSURE TO THE EAST OVER THE
MID ATLANTIC STATES. THE GFS KEEPS THE RIDGE MORE WESTWARD INTO THE
OHIO VALLEY...PREVENTING ISSAC FROM MAKING MUCH FORWARD PROGRESSION.
THE GFS SOLUTION WOULD KEEP ISSAC OVER OR NEARBY THE CWA THROUGH
LATE THURSDAY.

DUE TO THE UNCERTAINTY WITH THE LATE PERIOD FORECAST...HAVE MADE
ONLY MINOR ADJUSTMENTS TO POPS...KEEPING GOOD CHANCE POPS OVER THE
AREA THROUGH THURSDAY. HAVE ALSO MADE SOME VERY MINOR TWEAKS TO
TEMPERATURES THROUGH THE PERIOD BASED ON NEW RUN VALUES. PREVIOUS
FORECAST DISCUSSION INCLUDED BELOW...

31

/ISSUED 322 AM EDT THU AUG 23 2012/
ISAAC CONTINUES TO REMAIN THE FOCUS OF THE LONG TERM...HOWEVER
UNCERTAINTY IN FORECAST STILL EXISTS. AT THE BEGINNING OF THE LONG
TERM...H5 RIDGES SET UP ACROSS THE WESTERN CONUS AND ATLANTIC WITH
A WEAKNESS ACROSS THE SOUTHEAST. WITH TROUGH AXIS SHIFTED EAST OF
THE CWA AND SOME DRIER AIR REMAINING ACROSS THE AREA...CONVECTION
SHOULD REMAIN MINIMAL ACROSS THE AREA AND TEN TO TWENTY POPS
SHOULD COVER PRECIP THROUGH THE WEEKEND. AS WE GET INTO NEXT WEEK
THOUGH...UNCERTAINTY IN FORECAST GROWS WITH POTENTIAL IMPACTS FROM
ISAAC.

00Z GFS RUN HAS SHIFTED SLIGHTLY FURTHER WEST IN THE GULF. IT
SQUEEZES ISAAC BETWEEN THE TWO AFOREMENTIONED RIDGES AND ABSORBS THE
SYSTEM INTO THE TROUGH THAT SWINGS ACROSS THE EASTERN CONUS TUESDAY
INTO WEDNESDAY. ECMWF CONTINUES TO BE SLOWER AND FURTHER TO THE WEST
WITH ISAAC. THE MODEL ACTUALLY SWINGS THE TROUGH THROUGH THE CWA AND
PUSHES THE SYSTEM NORTHWARD BEHIND THE TROUGH AND INTO THE
RIDGE...REPOSITIONING THE ATLANTIC RIDGE AND PUSHING IT MORE INTO THE
SOUTHEAST. ECMWF SOLUTION WOULD KEEP MOST OF THE IMPACTS WEST OF THE
CWA...AT LEAST INITIALLY.

INITIALIZED LONG TERM WITH THE GFS SOLUTION AS ITS CLOSEST TO THE
OFFICIAL FORECAST TRACK. WITH THIS TRACK...GREATEST IMPACTS WOULD BE
FELT ACROSS THE CWA TUESDAY AND WEDNESDAY. GIVEN PLENTY OF TIME FOR
CHANGES IN THE MODELS AND UNCERTAINTY BETWEEN THE MODELS...TONED
DOWN THE INITIALIZED GRIDS FROM THE GFS TO LIMIT POPS TO CHANCE AT
THIS POINT. ALSO CONTINUED TO SOMEWHAT LIMIT WIND GRIDS AND OTHER
VARIABLES. AS SAID BEFORE...ALL THOSE IN THE SOUTHEAST WILL HAVE TO
CONTINUE TO MONITOR NHC FORECAST FOR ISAAC. AT THIS POINT
THOUGH...ITS JUST TOO FAR OUT AT THIS POINT TO DETERMINE EXACT
IMPACTS.

11

&&

.AVIATION...
18Z UPDATE...
LATEST SATELLITE AND RADAR LOOPS SHOWING ISOLATED CONVECTION
DEVELOPING ACROSS GEORGIA. ATL AREA AND CSG ALREADY SEEING IMPACTS
AND EXPECT VCSH OR POSSIBLE VCTS OR TEMPO TS WILL BE NECESSARY
20-24Z. WINDS WILL REMAIN OUT OF THE NE AT 3-9KTS. VFR CONDITIONS
ARE EXPECTED OUTSIDE OF ANY CONVECTION WITH MVFR POSSIBLE WITH THE
STRONGER STORMS.

//ATL CONFIDENCE...18Z UPDATE...
MEDIUM CONFIDENCE ON CONVECTION TIMING...MEDIUM TO HIGH CONFIDENCE
ALL OTHER ELEMENTS.

ATWELL

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          65  88  65  87 /  20  20   5  20
ATLANTA         69  87  68  85 /  10  10   5  20
BLAIRSVILLE     62  83  60  80 /  10  20   5  20
CARTERSVILLE    63  89  62  87 /   5  10   5  20
COLUMBUS        69  89  68  89 /   5  10   0  20
GAINESVILLE     67  85  66  84 /  10  20   5  20
MACON           67  89  66  89 /  20  20   5  20
ROME            62  90  63  90 /   5  10   5  20
PEACHTREE CITY  63  87  62  86 /  10  10   5  20
VIDALIA         69  88  69  87 /  20  20   5  20

&&

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

SHORT TERM...ATWELL
LONG TERM....31
AVIATION...ATWELL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
1227 PM EDT THU AUG 23 2012

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-241630-
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-
1227 PM EDT THU AUG 23 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH AND CENTRAL GEORGIA.

.DAY ONE...THIS AFTERNOON AND TONIGHT...
SCATTERED THUNDERSTORMS ACROSS CENTRAL GEORGIA AND ISOLATED
THUNDERSTORMS ACROSS NORTHEAST GEORGIA POSSIBLE THIS AFTERNOON
AND EVENING.

.SYNOPSIS...
A BOUNDARY WILL MEANDER AROUND CENTRAL GEORGIA TODAY.

.PRIMARY HAZARDS...
THE PRIMARY HAZARDS WILL BE GUSTY WINDS...HEAVY RAIN...AND
OCCASIONAL LIGHTNING MAINLY ALONG AND EAST OF A LINE FROM COLUMBUS
ATLANTA TO BLAIRSVILLE.

.DISCUSSION...
MOISTURE ACROSS THE AREA WILL ONCE AGAIN ALLOW FOR ISOLATED TO
SCATTERED THUNDERSTORMS THIS AFTERNOON AND EVENING MAINLY ACROSS
CENTRAL AND NORTHEAST GEORGIA. WITH A BOUNDARY MEANDERING ACROSS
CENTRAL GEORGIA...THE BEST CHANCE FOR THUNDERSTORMS WILL BE ACROSS
THAT AREA. INSTABILITY IS ON THE LOWER SIDE FOR SUMMER WITH CAPE
VALUES FORECAST TO BE AROUND 1000 J/KG THIS AFTERNOON. SEVERE
STORMS ARE NOT FORECAST AT THIS TIME.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY...
THERE IS A SLIGHT CHANCE OF THUNDERSTORMS THROUGH MONDAY. THE
CHANCE OF THUNDERSTORMS INCREASES FOR TUESDAY AND WEDNESDAY TO THE
CHANCE RANGE AS THE IMPACTS FROM ISAAC MAY REACH THE AREA.
ALTHOUGH THERE IS STILL UNCERTAINTY IN THE FORECAST...THE CURRENT
FORECAST TRACK WOULD BRING THE CHANCE OF FLOODING AND GUSTY WINDS
TO THE AREA. THOSE IN NORTH AND CENTRAL GEORGIA NEED TO CONTINUE TO
CLOSELY MONITOR THE FORECAST FOR ISAAC.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS NOT EXPECTED THROUGH TONIGHT.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
147 PM EDT THU AUG 23 2012

GAZ110-111-231815-
147 PM EDT THU AUG 23 2012

...SIGNIFICANT WEATHER ADVISORY FOR HEAVY RAIN IN WHEELER AND TELFAIR
COUNTIES UNTIL 215 PM EDT...

AT 143 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM OVER LUMBER CITY...MOVING SOUTHWEST AT 15 MPH.
WIND GUSTS TO NEAR 35 MPH ARE ALSO POSSIBLE.

RAINFALL AMOUNTS BETWEEN ONE TO TWO INCHES CAN BE EXPECTED ACROSS
WHEELER AND TELFAIR COUNTIES...INCLUDING AREAS AROUND SPRING
HILL...TOWNS...LUMBER CITY...HORSE CREEK WMA...WORKMORE AND
JACKSONVILLE. DRIVERS SHOULD USE CAUTION AS INTENSE RAINFALL WILL
REDUCE VISIBILITIES. PONDING OF WATER ON ROADWAYS IS ALSO LIKELY.

&&

LAT...LON 3178 8303 3179 8306 3187 8316 3207 8272
      3194 8258 3192 8261 3192 8267 3185 8275
      3185 8277 3183 8279 3178 8286 3178 8289
TIME...MOT...LOC 1747Z 053DEG 11KT 3191 8274

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
509 PM EDT THU AUG 23 2012

GAZ055-057-232145-
509 PM EDT THU AUG 23 2012

...SIGNIFICANT WEATHER ADVISORY FOR HEAVY RAIN IN HENRY AND CLAYTON
COUNTIES UNTIL 545 PM EDT...

AT 505 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM OVER HIDDEN VALLEY PARK...MOVING WEST AT 5 MPH.
WIND GUSTS TO 35 MPH ARE ALSO POSSIBLE.

RAINFALL AMOUNTS BETWEEN ONE TO TWO INCHES CAN BE EXPECTED ACROSS
HENRY AND CLAYTON COUNTIES...INCLUDING AREAS AROUND HIDDEN VALLEY
PARK...KELLEYTOWN...FLIPPEN...EAGLES
LANDING...STOCKBRIDGE...REX...FORT GILLEM...ELLENWOOD...LAKE
CITY...MORROW...LAKE SPIVEY...BONANZA...IRONDALE...JONESBORO AND
RIVERDALE. DRIVERS SHOULD USE CAUTION AS INTENSE RAINFALL WILL
REDUCE VISIBILITIES. PONDING OF WATER ON ROADWAYS IS ALSO LIKELY.

&&

LAT...LON 3365 8427 3365 8424 3363 8424 3365 8422
      3365 8419 3356 8413 3357 8411 3355 8408
      3351 8407 3343 8436 3362 8443
TIME...MOT...LOC 2109Z 075DEG 5KT 3357 8420

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
556 PM EDT THU AUG 23 2012

GAZ074-076-085-097-232230-
556 PM EDT THU AUG 23 2012

...SIGNIFICANT WEATHER ADVISORY FOR HEAVY RAIN IN WASHINGTON...
LAURENS...JOHNSON AND JEFFERSON COUNTIES UNTIL 630 PM EDT...

AT 554 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS FROM STELLAVILLE TO HARLOW...MOVING SOUTHWEST
AT 5 MPH. WIND GUSTS TO NEAR 35 MPH ARE ALSO POSSIBLE.

RAINFALL AMOUNTS BETWEEN ONE TO TWO INCHES CAN BE EXPECTED ACROSS
WASHINGTON...LAURENS...JOHNSON AND JEFFERSON COUNTIES...INCLUDING
AREAS AROUND LOVETT...HARLOW...BREWTON...EAST DUBLIN...DUBLIN...NEW
HOME...SPANN...DONOVAN...WRIGHTSVILLE...MOXLEY...BARTOW...LOUISVILLE.
..PRINGLE...RENTZ AND MATTHEWS. DRIVERS SHOULD USE CAUTION AS
INTENSE RAINFALL WILL REDUCE VISIBILITIES. PONDING OF WATER ON
ROADWAYS IS ALSO LIKELY.

&&

LAT...LON 3305 8228 3231 8290 3248 8315 3322 8243
      3324 8223
TIME...MOT...LOC 2155Z 082DEG 4KT 3317 8230 3279 8272
          3249 8300