Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 251121
AFDFFC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
721 AM EDT SAT APR 25 2015



.PREV DISCUSSION... /ISSUED 341 AM EDT SAT APR 25 2015/

SHORT TERM /TODAY THROUGH SUNDAY/...
COMPLICATED SURFACE PATTERN ACROSS THE EASTERN HALF OF THE THE U.S.
ACROSS THE CWFA...HIGH PRESSURE HAS MOVED OFFSHORE AND AN OLD NEARLY
DIFFUSE SURFACE BOUNDARY IS ACROSS NORTHERN GA. FURTHER WEST...LOW
PRESSURE ACROSS THE PLAINS STATES WILL MOVE EAST TODAY ALONG ANOTHER
OLD SURFACE BOUNDARY...INTO THE TN AND OH VALLEYS. REGIONAL RADAR
SHOWS A LARGE AREA OF CONVECTION...AN MCS...MOVING EAST/SLIGHTLY
NORTHEAST ACROSS MISSISSIPPI INTO WESTERN AL.

IN THE MID LEVELS...AN UPPER LOW/STRONG SHORTWAVE ACROSS THE CENTRAL
U.S. WILL MOVE EAST INTO THE TN/OH VALLEYS. FURTHER SOUTH...STRONG
SHORTWAVE ENERGY ASSOCIATED WITH THE MCS CURRENTLY ACROSS
MISSISSIPPI WILL CONTINUE TO TREK EASTWARD/SLIGHTLY NORTHEASTWARD
THIS MORNING. DON`T THINK THAT THE SYNOPTIC OR HI-RES MODELS
INITIALIZED THIS FEATURE VERY WELL. IN ADDITION...THE MID LEVEL
LAPSE RATES ARE SOMEWHAT STEEPER THAN PROGGED.

SPEAKING OF THE HI-RES MODELS...THEY ALL HAVE DIFFERENT SOLUTIONS
FOR TODAYS SYSTEM...ESPECIALLY THE AFTERNOON CONVECTION. ALL OF THE
HI-RES MODELS AGREE THAT THE ACTIVITY MOVING IN FROM ALABAMA WILL
IMPACT THE CWFA BY AROUND 09Z. THE SECOND AREA OF STRONGER
CONVECTION...BACK OVER MISSISSIPPI...DRIVEN BY THE STRONG SHORTWAVE
ENERGY MAY NOT WEAKEN AS MUCH AS SOME OF THE HI-RES MODELS ARE
PROGGING. AT THIS TIME...THE WRF SEEMS TO HAVE A PRETTY DECENT
HANDLE ON WHAT IS GOING ON NOW...INCLUDING THE STRONGER ACTIVITY
ACROSS MISSISSIPPI. SO...HAVE LEANED CLOSER TO THE WRF SOLUTION FOR
THE VERY SHORT TERM PORTION OF THE FORECAST.

THE AFTERNOON FORECAST BECOMES A LITTLE MORE MURKY. BELIEVE
AFTERNOON CONVECTION WILL DEPEND VERY HEAVILY ON THAT HAPPENS THIS
MORNING. THE HI-RES MODELS REALLY BEGIN TO DIVERGE AT THIS POINT.
ALL THE PARAMETERS FOR SEVERE WEATHER WILL BE IN PLACE...INCLUDING
FAVORABLE CONDITIONS FOR A FEW TORNADOES. HOWEVER...EXACTLY
WHEN/WHERE THE AFTERNOON CONVECTION WILL DEVELOP IS THE DIFFICULT
PART OF THE FORECAST. CONVECTIVE INITIATION FOR THE AFTERNOON WILL
DEPEND HEAVILY ON ANY OUTFLOW/DIFFERENTIAL HEATING BOUNDARIES THAT
THE OVERNIGHT/EARLY MORNING CONVECTION LAYS DOWN. THIS COULD BE A
PRIMARY FOCUS FOR CONVECTION/SURFACE CONVERGENCE.

AS MENTIONED BEFORE...ALL OF THE PARAMETERS FOR SEVERE WEATHER WILL
BE PRESENT TODAY...ESPECIALLY IN THE AFTERNOON. GOOD LOW LEVEL
SHEAR/HELICITY AND STRONG SURFACE INSTABILITY WHERE GOOD HEATING
WILL OCCUR. PLUS...A SURFACE BOUNDARY FOR CONVECTION TO FOCUS UPON.
DAMAGING WIND GUSTS WILL BE LIKELY WITHIN ANY SEVERE THUNDERSTORMS.
WITH THE STRONG SHEAR PRESENT...A FEW TORNADOES ARE NOT OUT OF THE
QUESTION. THE BEST/STRONGEST MID LEVEL SHORTWAVE ENERGY SHOULD BE
ACROSS THE OH/TN VALLEYS...SO THE BEST CHANCES FOR LARGE HAIL SHOULD
BE TO THE NORTH OF THE CWFA. HOWEVER...SINCE MID LEVEL LAPSE RATES
ARE CURRENTLY STEEPER THAN THE MODELS CURRENTLY HAVE
FORECAST...WOULDN`T RULE OUT A LARGE HAIL PRODUCING THUNDERSTORM AT
THIS TIME.

CONVECTION SHOULD LAST INTO THE EVENING HOURS...ALONG WITH THE
CHANCES FOR SEVERE WEATHER. DO EXPECT ACTIVITY TO LOSE SOME STEAM
WITH THE LOSS OF HEATING...BUT MAY NOT COMPLETELY DIMINISH WITH THE
SETTING OF THE SUN. HAVE LEFT SOME POPS IN FOR SUNDAY...AS THE
ACTUAL FRONTAL BOUNDARY DOESN`T MOVE THROUGH UNTIL THEN.

NLISTEMAA

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
WEAK RIDGING AT THE SFC AND MOSTLY DRY CONDITIONS TO BEGIN THE LONG
TERM. SHORTWAVE SLIDES FROM THE MS VALLEY INTO THE TN VALLEY TUESDAY
NIGHT INTO WEDNESDAY WHILE A SFC LOW TRACKS ALONG THE GULF COAST.
THIS RESULTS IN THE RETURN OF SHOWERS AND THUNDERSTORMS TUESDAY
NIGHT INTO WEDNESDAY NIGHT. GFS IS SLOWER THAN MODEL RUN LAST NIGHT
IN CLEARING OUT THE PRECIPITATION AND HOLDS ONTO IT THROUGH THURSDAY
NIGHT. ALTHOUGH THERE ARE SLIGHT DIFFERENCES IN FEATURES BETWEEN THE
GFS AND THE ECMWF THE TIMING OF DIMINISHING PRECIPITATION IS FAIRLY
SIMILAR. HIGH PRESSURE BUILDS IN BEHIND THAT SYSTEM AND SHOULD LEAD
TO A FEW DRY DAYS.

11


&&

.AVIATION...
12Z UPDATE...
MCS CURRENTLY MOVING THROUGH THE CWFA. EMBEDDED THUNDERSTORMS
SHOULD ONLY LAST UNTIL 13Z OR SO...BUT THE SHOWERS MAY LINGER A
LITTLE LONGER. HI-RES MODELS ARE ALL OVER THE PLACE WITH THE
DEVELOPMENT OF AFTERNOON CONVECTION. CONFIDENCE IS LOW ON THE
WHEN/WHERE CONVECTION WILL INITIATE. WINDS WILL FLIRT WITH DUE
SOUTH THIS MORNING. THE CURRENT RAINFALL MAY REINFORCE THE SE
WINDS FOR A FEW HOURS LONGER...BUT SUSTAINED SPEEDS SHOULD BE
PRETTY LIGHT. A SWITCH OVER TO THE SW SHOULD OCCUR BY THE EARLY


//ATL CONFIDENCE...12Z UPDATE...
LOW CONFIDENCE ON WHEN/WHERE AFTERNOON CONVECTION WILL OCCUR.
MEDIUM CONFIDENCE REMAINING ELEMENTS.


&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          74  63  81  55 /  90  50  20  10
ATLANTA         75  65  80  56 / 100  30  20   5
BLAIRSVILLE     68  58  71  46 / 100  50  20  10
CARTERSVILLE    76  63  78  51 / 100  30  20  10
COLUMBUS        80  67  85  60 /  90  30  30   5
GAINESVILLE     71  63  77  54 / 100  40  20   5
MACON           79  67  86  58 /  90  50  30   5
ROME            75  62  78  51 / 100  30  20   5
PEACHTREE CITY  77  64  82  54 / 100  30  20   5
VIDALIA         81  69  87  62 /  90  50  30  10

&&

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

$$


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