Special Weather Statement, NWS Atlanta, GA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
703 PM EST SUN FEB 10 2013

.PREV DISCUSSION...

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
/ISSUED 247 PM EST SUN FEB 10 2013/
OF COURSE THE MAIN CONCERN OF THE SHORT TERM IS THE HEAVY RAIN THAT
WILL BE MOVING IN THIS AFTERNOON AND EVENING. A SECONDARY CONCERN IS
POTENTIAL FOR STRONG STORMS. FOR DAYS NOW GUIDANCE HAS BEEN POINTING
TO THE CUTOFF LOW IN THE UPPER MIDWEST MOVING TOWARD THE GREAT
LAKES...WITH A TRAILING COLD FRONT DRAGGING ACROSS THE MID-SOUTH AND
INTO THE SOUTHEAST OVERNIGHT TONIGHT. UPPER RIDGING ACROSS THE
CARIBBEAN WITH THE TROUGHINESS OVER THE CENTRAL PORTION OF THE
COUNTRY HAS LED TO DEEP SOUTHWEST FLOW ALOFT WITH STRONG 50-60KT LOW
LEVEL JET MOVING ACROSS THE AREA.

MOISTURE WILL INCREASE SIGNIFICANTLY THIS AFTERNOON WITH PW VALUES
RANGING FROM 1.4 /NAM/ TO 1.6 /GFS/. EITHER VALUE IS ABOVE THE 99TH
PERCENTILE BASED ON CLIMATOLOGICAL PW VALUES WITH 1.6 BEING ABOVE
THE MAX CLIMATOLOGICAL PW. WITH THESE PW VALUES...RAIN RATES COULD
BE ANOMALOUSLY HIGH AND MODEL QPFS MIGHT NOT BE ABLE TO CAPTURE WHAT
IS GOING ON. SOME OBSERVATIONS FROM THE LOWER SOUTH HAVE INDICATED
RATES OF 0.5-1 INCH PER HOUR IN THE MORE CONVECTIVE CELLS. WITH
THIS...AM DEFINITELY CONCERNED ABOUT FLOOD/FLASH FLOOD POTENTIAL...
ESPECIALLY WITH THE MAIN SURGE OF PRECIP MOVING IN FROM 00-06Z
TONIGHT ACROSS NORTH GEORGIA. GFS QPF IS ON THE HIGH SIDE /ALMOST 3
INCHES/ BUT GFS ALSO HAS A LOW PV ANOMALY /AND CONVECTIVE FEEDBACK/
CONTRIBUTING TO ITS HIGHER QPF...AS IS TYPICAL. THAT SAID...EVEN
THE SREF HAS WIDESPREAD 0.75-1 INCH FROM 00-06Z TONIGHT. BY THE
NATURE OF ENSEMBLE GUIDANCE...SREF IS TYPICALLY LOWER THAN
DETERMINISTIC GUIDANCE SO THIS IS A BIT CONCERNING. 12Z ECMWF HAS
ALSO SLOWED DOWN TIMING FROM ITS PREVIOUS RUNS. HAVE INCREASED AND
SLOWED DOWN HPC QPF VALUES BUT DO NOT HAVE A GREAT HANDLE ON WHAT
MIGHT HAPPEN. WE CONTINUE TO ADVERTISE WIDESPREAD 2-4 INCHES
OVERNIGHT TONIGHT BUT RESIDENTS ACROSS NORTH GEORGIA SHOULD REMAIN
ALERT IN CASE HIGHER AMOUNTS ARE OBSERVED. SEE HYDROLOGY SECTION
BELOW FOR MORE ON IMPACTS.

AS FOR THUNDER POTENTIAL...MUCAPE VALUES ON ALL MODELS REMAIN
GENERALLY BELOW 800 J/KG...WITH THE GFS LOWEST AND NAM HIGHEST AS
USUAL. THAT SAID HOWEVER...SEEING QUITE A BIT OF LIGHTNING OUT IN
MISSISSIPPI AND ALABAMA SO WENT AHEAD AND KEPT SLIGHT CHANCE THUNDER
IN MOST OF THE GRIDS THIS EVENING AND OVERNIGHT. WITH THE LOW LEVEL
JET SETTING UP FOR OVERNIGHT...THE AMOUNT OF SHEAR MOVING INTO THE
AREA INCREASES ESPECIALLY ACROSS WEST CENTRAL GEORGIA AS THE FRONT
APPROACHES. TIMING OF THE FRONT IS GENERALLY AFTER MIDNIGHT TO MOVE
INTO GEORGIA...AND WITH BEST STRONG TO POTENTIAL SEVERE WEATHER
THREAT LINING UP WITH THE FRONT THIS WARRANTS KEEPING THUNDER IN
OVERNIGHT. SPC SLIGHT RISK FOR DAY1 GOES RIGHT UP TO THE BORDER WITH
ONLY MINIMAL SEVERE PROBS PUSHING INTO WEST CENTRAL GEORGIA. USED A
NAM/GFS BLEND TO CALCULATE EXPERIMENTAL SHERB /SEVERE HAZARDS IN
ENVIRONMENTS WITH REDUCED BUOYANCY - DEVELOPED LIKE STP WITH VALUES
GREATER THAN 1 MEANING HIGH SHEAR-LOW CAPE SEVERE WEATHER POSSIBLE/
PARAMETER AND AFTER 00Z DO SEE AN AREA OF GREATER THAN 1 NOSING INTO
WEST CENTRAL GEORGIA WITH VALUES HOVERING NEAR 1 THROUGH 06Z
ESPECIALLY ACROSS CENTRAL GEORGIA. THAT SAID...DO NOT EXPECT MUCH IN
THE WAY OF SEVERE WEATHER BUT CANNOT RULE OUT A DAMAGING WIND GUST
OR TWO. OTHER CONCERN WOULD BE DUE TO THE VERY STRONG LOW LEVEL
JET...50-60KT AT 925MB...COULD STILL SEE STRONG GUSTS COMING DOWN
WITH THE RAIN EVEN WITHOUT THUNDER OR OTHERWISE CONVECTIVE WEATHER.
CURRENT WIND/WIND GUSTS GRIDS NOT ENOUGH FOR WIND ADVISORY CRITERIA
BUT THESE MAY BE TOO LOW DEPENDING ON HOW MUCH OF THE JET ABOVE IS
ABLE TO PENETRATE TO THE SURFACE.

TDP

LONG TERM /TUESDAY THROUGH SUNDAY/...
/ISSUED 247 PM EST SUN FEB 10 2013/
A SERIES OF DISTURBANCES WILL BRING A COUPLE OF CHANCES FOR HEAVY
RAIN TO MAINLY CENTRAL GA TUESDAY THROUGH WEDNESDAY. AT THIS
TIME... BOTH GFS AND ECMWF SEEM TO BE TARGETING MAINLY CENTRAL GA
WITH THE HEAVIEST RAINFALL AMOUNTS... WHERE MODEL GUIDANCE AND HPC
ARE INDICATING 2-4 INCHES ARE POSSIBLE OVER THIS TIME PERIOD.
ALTHOUGH CENTRAL GA SEEMS TO BE TAKING THE HEAVIES RAINFALL
AMOUNTS... ITS IMPORTANT TO NOTE THAT ANY ADDITIONAL RAINFALL OVER
NORTH GA WILL JUST ADD TO ANY ON-GOING FLOOD PROBLEMS THERE. THESE
RAINFALL AMOUNTS OVER CENTRAL GA COULD ALSO RESULT IN SOME MINOR
FLOOD PROBLEMS THERE... AND TYPICAL FLOOD PRONE AREAS SHOULD BE
CLOSELY MONITORED. THURSDAY STILL LOOKS DRY...THEN BOTH GFS AND
ECMWF SHOW A COUPLE OF FAST MOVING DISTURBANCES BRINGING A SLIGHT
CHANCE OF LIGHT RAIN OR SNOW TO THE FAR NORTHERN COUNTIES EARLY
SATURDAY MORNING AND AGAIN EARLY SUNDAY MORNING. AT THIS TIME...
STILL MUCH UNCERTAINTY ON AVAILABLE MOISTURE... SO LITTLE TO NO
ACCUMULATIONS ARE EXPECTED... BUT WILL BARE WATCHING.

39

HYDROLOGY...
/ISSUED 247 PM EST SUN FEB 10 2013/
STILL EXPECTING AROUND 2-4 INCHES OF STORM TOTAL PRECIP ACROSS
MUCH OF NORTH GA TONIGHT... WITH ISOLATED HIGHER AMOUNTS POSSIBLE.
THESE AMOUNTS OVER ALREADY MOIST SOIL CONDITIONS WILL LIKELY CAUSE
FLOOD PROBLEMS...WITH TYPICAL CREEKS AND STREAMS ACROSS NORTH GA
GOING INTO FLOOD OVERNIGHT... WITH ADDITIONAL WATERWAYS EXPERIENCING
A SLOWER RISE BUT STILL REACHING FLOOD STAGE ON MONDAY. FLASHY
AREAS IN NORTH AND NORTHWEST GEORGIA...SPECIFICALLY LOOKOUT CREEK
AND WEST CHICKAMAUGA CREEK...WILL LIKELY NEED WARNINGS TONIGHT.
BIG CREEK AT ALPHARETTA IS FORECAST TO GO INTO FLOOD ON MONDAY. AS
THE HEAVIEST RAIN SHIFTS SOUTH DURING THE DAY ON MONDAY... SHOULD
START TO SEE RISES ON OTHER CREEKS. HAVE LEFT THE FLASH FLOOD
WATCH IN EFFECT FROM 7 PM THIS EVENING THROUGH 1 PM MONDAY WHEN
THE HEAVIEST RAINS ARE EXPECTED.

&&

.AVIATION...
00Z UPDATE...
LINE OF STRONGER SHOWERS MOVING THROUGH ATL AREA. TS IS VERY
ISOLATED BUT WITH TS IN THE ATL AREA HAVING BEEN REPORTING DID
INCLUDE THIS WITH THE STRONGER LINE OF SHOWERS. CHANCE OF TS
SHOULD DIMINISH BEHIND THIS LINE. WINDS WITH THE LINE WILL LIKELY
BRIEFLY SHIFT FROM THE EAST SIDE TO NW BUT SHOULD LAST FOR NO MORE
THAN ONE HOUR. ONCE THIS LINE COMES THROUGH WILL SEE RA CONTINUE
THROUGH THE MORNING WITH CIGS DECREASING TO IFR OVERNIGHT. LARGE
UNCERTAINTY IN THE VSBY FORECAST...ESPECIALLY THROUGH ABOUT 15Z
TOMORROW.

//ATL CONFIDENCE...00Z UPDATE...
MEDIUM CONFIDENCE ON CIGS. LOW CONFIDENCE ON VSBYS. MEDIUM
CONFIDENCE ON TIMING OF WIND SHIFT.

11

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          53  63  43  55 / 100  90  30  60
ATLANTA         55  64  45  55 / 100  90  50  80
BLAIRSVILLE     47  61  37  55 / 100  50  20  50
CARTERSVILLE    53  62  41  58 / 100  60  30  60
COLUMBUS        63  67  49  58 / 100 100  70  90
GAINESVILLE     50  64  43  54 / 100  70  30  60
MACON           59  68  48  58 / 100 100  70  90
ROME            50  62  40  58 / 100  40  30  60
PEACHTREE CITY  58  64  42  54 / 100 100  60  80
VIDALIA         58  72  52  60 /  50  80  70  80

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH MONDAY AFTERNOON FOR THE FOLLOWING
ZONES: BANKS...BARROW...BARTOW...CARROLL...CATOOSA...CHATTOOGA...
CHEROKEE...CLARKE...COBB...DADE...DAWSON...DEKALB...DOUGLAS...
FANNIN...FLOYD...FORSYTH...GILMER...GORDON...GWINNETT...HALL...
HARALSON...JACKSON...LUMPKIN...MADISON...MURRAY...NORTH FULTON...
OCONEE...OGLETHORPE...PAULDING...PICKENS...POLK...ROCKDALE...
SOUTH FULTON...TOWNS...UNION...WALKER...WALTON...WHITE...
WHITFIELD.

&&

SHORT TERM...TDP/11
LONG TERM....39
AVIATION...11

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
520 AM EST SUN FEB 10 2013

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-111100-
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-
520 AM EST SUN FEB 10 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH AND CENTRAL GEORGIA.

.DAY ONE...TODAY AND TONIGHT...

.WEATHER HAZARDS EXPECTED...
FLASH FLOODING POSSIBLE ACROSS NORTH GEORGIA TONIGHT.
ISOLATED STRONG THUNDERSTORMS POSSIBLE ACROSS PORTIONS OF NORTH AND
CENTRAL GEORGIA TONIGHT.

.DISCUSSION...
A WARM FRONT MOVING NORTH AHEAD OF A COLD FRONT WILL BRING A PERIOD
OF MODERATE TO HEAVY RAIN ACROSS NORTH GEORGIA...MAINLY TONIGHT. 2
TO 3 INCHES OF RAIN CAN BE EXPECTED AND FLASH FLOODING IS POSSIBLE.
ALSO ISOLATED STRONG THUNDERSTORMS ARE POSSIBLE OVER PORTIONS OF
NORTH AND CENTRAL GEORGIA DUE TO STRONG WIND SHEAR AND WEAK
INSTABILITY.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY...
MODERATE TO HEAVY RAIN WILL CONTINUE ACROSS THE AREA AND SHIFT MORE
TO CENTRAL GEORGIA FROM LATER MONDAY INTO TUESDAY...WITH POTENTIAL
FLOODING CONCERNS CONTINUING. THUNDERSTORMS WILL BE POSSIBLE OVER
CENTRAL AND PORTIONS OF NORTH GEORGIA MONDAY AND PORTIONS OF NORTH
AND CENTRAL GEORGIA TUESDAY INTO WEDNESDAY. A PERIOD OF WINDY
CONDITIONS CAN BE EXPECTED ON WEDNESDAY AND AGAIN ON FRIDAY AND
SATURDAY.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME. SPOTTERS AND
EMERGENCY MANAGERS SHOULD MONITOR THE LATEST WEATHER UPDATES.

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