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000
FXUS62 KFFC 190542
AFDFFC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
142 AM EDT SUN MAY 19 2013



.PREV DISCUSSION... /ISSUED 1009 PM EDT SAT MAY 18 2013/

UPDATE...
HI RES MODELS HAVE NOT BEEN HANDLING THE CONVECTION WELL AT ALL
THIS EVENING AND WERE OVERDOING IT THIS AFTERNOON. HRRR HAS
PROBABLY BEEN THE BEST BUT STILL NOT QUITE CATCHING TRENDS.
STARTING TO SEE MORE DEVELOPMENT OVER THE PAST HOUR...PARTICULARLY
ACROSS NORTHWEST GEORGIA. SHOULD SEE AN INCREASE IN COVERAGE BY
SUNRISE. STILL NOT CONFIDENT ON WHAT IS GOING TO HAPPEN TOMORROW
IN TERMS OF CONVECTION. A FEW MODELS ARE LIMITING ACTIVITY...WHILE
SOME ARE SHOWING A MORE ACTIVE AFTERNOON. MAIN CHANGE TO THE
FORECAST TONIGHT WAS TO DECREASE POPS INITIALLY BUT SHOW A TREND
OF INCREASING POPS LATE TONIGHT. TWEAKED TOMORROW AND TOMORROW
EVENING BY TRYING TO SHOW A TREND OF DECREASING POPS ACROSS THE
WESTERN PART OF THE CWA LATE IN THE DAY. GIVEN FORECAST
INSTABILITY...HAVE CONTINUED MENTION OF SLIGHT CHANCE OF THUNDER
OVERNIGHT TONIGHT.

11

PREV DISCUSSION...

SHORT TERM /TONIGHT THROUGH SUNDAY/...
/ISSUED 326 PM EDT SAT MAY 18 2013/
WEAK UPPER LOW OVER THE TENNESSEE VALLEY IS SLOWLY PULLING EAST.
WEAK DISTURBANCES ROTATING THROUGH THE FLOW OVER AL AND GA WAS
PRODUCING SCATTERED SHOWERS/TSTORMS. THE PRECIP SHOULD DIMINISH THIS
EVENING...BUT AS ANOTHER WEAK WAVE MOVES INTO SOUTHEAST TENNESSEE
LATE TONIGHT...EXPECT CONVECTION TO INCREASE ACROSS NORTH GA AND
SPREAD SOUTH AND EAST SUNDAY. MODELS ARE RATHER CONSERVATIVE WITH
THE POPS AND HAVE CONTINUED WITH LIKELY POPS FOR SUNDAY. AT THIS
TIME EXPECT A FEW STORMS TO BE STRONG AND AN ISOLATED SEVERE STORM
IS STILL NOT OUT OF THE QUESTION SUNDAY AFTERNOON...MAINLY ACROSS
WEST CENTRAL GA. THERE REMAINS PLENTY OF ISENTROPIC LIFT AND K-INDEX
VALUES ARE QUITE HIGH AND THEREFORE EXPECT SOME HEAVY RAIN IN SOME
OF THE STRONGER STORMS. WITH LITTLE SURFACE WIND TONIGHT AND PLENTY
OF SURFACE MOISTURE...EXPECT FOG/STRATUS TO DEVELOP ACROSS WEST
CENTRAL GEORGIA WHICH SHOULD SPREAD NORTH AND EAST LATE TONIGHT.

17

LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...

NO CHANGES NEEDED TO THE PREVIOUS EXTENDED FORECAST RATIONALE.

16

HAVE ADJUSTED POPS UPWARD FOR SUNDAY NIGHT ACROSS THE CWFA.
MODELS ARE SHOWING SIGNS OF AN MCS DEVELOPING IN THE NW FLOW AND
AFFECTING THE CWFA. STRONG SURFACE INSTABILITY AND VERY STEEP
LAPSE RATES WILL HELP SUSTAIN CONVECTION AND CONTINUE THE
POSSIBILITY OF SEVERE STORMS AT LEAST THROUGH MIDNIGHT.

FOR MONDAY...A 500MB TROUGH/SHEAR AXIS SETS UP RIGHT ALONG THE SE
COAST. THIS FEATURE SHOULD SERVE TO FOCUS ANY CONVECTIVE ACTIVITY
FOR MONDAY AND MONDAY EVENING. DO THINK SHRA/TSRA WILL BE MORE
DIURNAL IN NATURE. KEPT THE TREND OF HIGHEST POPS IN THE EAST...WITH
ONLY ISOLATED ACTIVITY TO THE WEST.

WEAK SHEAR AXIS/500MB TROUGH MOVES OFF THE COAST ON TUESDAY WITH
RIDGING BUILDING ALOFT ACROSS THE CWFA. ANY CONVECTION SHOULD BE
ISOLATED IN NATURE...SURFACE INSTABILITY WILL BE PRESENT BUT NO
DISCERNIBLE SURFACE MECHANISM TO FOCUS PRECIP IS NOTED. PRECIP
SHOULD BE DIURNAL.

UNCERTAINTY BEGINS TO CREEP INTO THE FORECAST BY WEDNESDAY. EARLIER
MODEL RUNS PROGGED A COLD FRONT TO MOVE THROUGH THE CWFA DURING THE
LATTER HALF OF THE WEEK. THE ECMWF NOW KEEPS THE FRONT TO THE
NORTH...WHILE THE GFS DOES MOVE THE BOUNDARY THROUGH SLOWLY FRIDAY
THROUGH SATURDAY. HAVE OPTED TO GO PERSISTENCE FOR THIS PERIOD DUE
TO LOW CONFIDENCE.

NLISTEMAA


&&

.AVIATION...
06Z UPDATE...
CURRENT PATTERN MAKES IT DIFFICULT TO FORECAST THE TIMING OF
CONVECTION. FOLLOWED THE LATEST RUN OF THE HRRR FAIRLY CLOSELY FOR
CONVECTIVE ELEMENTS...OVER THE LAST FEW DAYS...IT HAS BEEN THE
BEST MODEL. CIGS AND WINDS WILL ALSO BE A CHALLENGE. MODELS DO
HAVE CIG VALUES DIPPING TO IFR AND OBS REFLECT THIS...ALSO AREAS
OF FOG WILL BE PRESENT BUT ONLY HAVE 5-6SM PREV. MORNING
CONVECTION MAY LIMIT AFTERNOON DEVELOPMENT.

//ATL CONFIDENCE...06Z UPDATE...
LOW CONFIDENCE ON CIGS AND TIMING OF SHRA/TSRA. MEDIUM CONFIDENCE
REMAINDER OF ELEMENTS.

NLISTEMAA

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          77  65  84  66 /  60  50  30  20
ATLANTA         81  66  86  66 /  60  30  20  10
BLAIRSVILLE     76  60  82  61 /  70  50  30  20
CARTERSVILLE    81  65  88  67 /  60  30  20  20
COLUMBUS        86  67  89  68 /  40  30  20  10
GAINESVILLE     77  63  84  65 /  70  50  30  20
MACON           83  66  87  66 /  50  30  30  10
ROME            82  65  89  67 /  60  30  20  20
PEACHTREE CITY  82  65  87  66 /  50  30  20  10
VIDALIA         86  68  84  65 /  50  50  40  20

&&

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

$$

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