000
FXUS62 KFFC 180614
AFDFFC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
214 AM EDT SAT MAY 18 2013



.PREV DISCUSSION... /ISSUED 920 PM EDT FRI MAY 17 2013/

UPDATE...
RE-ADJUSTED POPS AND WEATHER GRIDS TO ACCOUNT FOR CURRENT TRENDS...
BETTER CONVECTION IS SHIFTING SOUTH ACROSS ALABAMA ALONG THE BETTER
THETA-E AXIS. PLENTY OF LIGHT TO MODERATE SHOWERS STILL MOVING INTO
WESTERN PORTIONS OF THE FORECAST AREA...AND CANNOT RULE OUT SOME
THUNDER THROUGH THE OVERNIGHT WITH THE UPPER LOW SPINNING IN THE
VICINITY. THE REMAINDER OF THE FORECAST LOOKS OK FOR NOW SO LITTLE OR
NO CHANGES MADE AT THIS TIME.

20

PREV DISCUSSION... /ISSUED 805 PM EDT FRI MAY 17 2013/

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
SCATTERED TO BROKEN CLOUD COVER PREVAILED OVER NORTH AND CENTRAL GA
AT THIS TIME WITH A FEW LIGHT SHOWERS. THE UPPER LEVEL TROUGH OVER
THE MS RIVER VALLEY HAS ASSOCIATED SHORT WAVES ROTATING THROUGH
NORTH AL AND CENTRAL TN WITH NUMEROUS SHOWERS AND SCATTERED TSTMS.
MOST MODELS ARE IN AGREEMENT THE TROUGH WILL GRADUALLY MOVE EAST
THROUGH SATURDAY NIGHT. THE UPPER LEVEL DISTURBANCES WILL COMBINE
WITH ADEQUATE GULF MOISTURE...PWS AROUND 1.5 INCHES...TO SPREAD
NUMEROUS SHOWERS AND SCATTERED TSTMS OVER THE NORTH HALF OF GA. WILL
LEAN TOWARD THE NAM...HRRR AND LOCAL WRF MODEL SOLUTIONS WHICH
EXPECT THE SHOWERS AND A FEW TSTMS TO ENTER NORTHWEST GA TONIGHT AND
OVER MOST OF NORTH GA BY MIDNIGHT. THE TSTM POTENTIAL SHOULD
DIMINISH TO ISOLATED LATER TONIGHT AS THE RAIN COOLED AIR STABILIZES
THE AIRMASS OVER THE STATE. DIURNAL HEATING ON SATURDAY WILL TRIGGER
ADDITIONAL TSTMS IN THE AFTERNOON AND EVENING WITH MUCAPES IN THE
1500-2000 J/KG RANGE. A SLIGHT RISK OF SEVERE TSTMS WILL BE
POSSIBLE...MAINLY OVER NORTHWEST GA DUE TO THE CLOSE PROXIMITY OF
THE UPPER LEVEL TROUGH. QPF AMOUNTS OF 1 TO 1.5 INCHES ARE EXPECTED
OVER NORTH GA WITH 0.75 INCH OR LESS OVER CENTRAL GA. TEMPORARY
STREET FLOODING WILL BE POSSIBLE WITH PERIODS OF HEAVY
RAIN...HOWEVER CREEK OR RIVER FLOODING SHOULD BE LIMITED UNLESS MORE
QPF DEVELOPS IN A MUCH SHORTER PERIOD OF TIME. A MET/MAV MOS BLEND
WAS USED FOR MIN AND MAX TEMPS.

16

LONG TERM /SUNDAY THROUGH FRIDAY/...
SHORTWAVE IS IN THE PROCESS OF SHIFTING EAST OF THE CWA ON
SUNDAY...SO THIS...IN ADDITION TO PLENTY OF MOISTURE ACROSS THE
CWA AND FORECAST MUCAPE AROUND 3000 J/KG WILL ALLOW FOR THE TREND
OF SHOWERS AND THUNDERSTORMS TO CONTINUE INTO SUNDAY. HAVE
EXTENDED LIKELY POPS FURTHER WEST THAN PREVIOUS FORECAST FOR
SUNDAY. WITH UPPER RIDGE BUILDING IN FOR MONDAY AND
TUESDAY...POPS DECREASE...BUT THERE IS ENOUGH MOISTURE AROUND TO
KEEP SLIGHT CHANCE TO CHANCE POPS. GFS AND ECMWF STILL DIFFER
WITH MID-WEEK FRONTAL BOUNDARY WITH THE ECMWF FASTER THAN THE GFS
IN THE 12Z RUN. GIVEN DIFFERENCES...HAVE CONTINUED THE TRENDS
ADVERTISED IN THE PREVIOUS FORECAST. THE PREVIOUS DISCUSSION FOLLOWS.

11

LONG TERM /SATURDAY THROUGH THURSDAY/...
MODELS IN GENERAL AGREEMENT FOR SATURDAY TARGETING THE AREA WITH
SCATTERED TO NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS. THIS
DUE TO THE INFLUENCE OF UPPER LOW PRESSURE MOVING TO THE OH/TN
VALLEY AREAS AND THE MAIN UPPER TROUGH AFFECTING GA. WHILE N GA IS
TARGETED WITH THE HIGHEST POPS...INSTABILITY ACROSS THE AREA WILL
ALLOW FOR SCATTERED SHOWERS/STORMS ACROSS CENTRAL GA AS WELL. EVEN
WITH CLOUDS AND PRECIP CHANCES...A WARM AIRMASS IN PLACE WILL
ALLOW FOR HIGH TEMPERATURES NEAR NORMAL.

UPPER SYSTEM IN THE PROCESS OF PASSING THE AREA FOR SUNDAY BUT STILL
PLENTY OF MOISTURE AND INSTABILITY IN PLACE FOR SCATTERED TO
NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS. MODELS IN SOME
DISAGREEMENT FOR MONDAY WITH THE GFS WETTER THAN THE EUROPEAN AS THE
EUROPEAN HAS A STRONGER DRIER UPPER RIDGE MOVING OVER THE AREA THAN
THE GFS. GFS CONTINUES TO BE WETTER ON TUESDAY THAN THE EUROPEAN
WITH THE INFLUENCE OF AN UPPER RIDGE OVER THE AREA. STILL PLENTY OF
MOISTURE AND INSTABILITY FOR SOME AFTERNOON/EVENING CONVECTION.
INFLUENCE OF THE UPPER RIDGE DIMINISHES ON WEDNESDAY AS A COLD FRONT
MOVES ACROSS THE MID U.S. THIS WILL ALLOW FOR THE CHANCES OF SHOWERS
AND STORMS ACROSS THE AREA WITH CHANCES A LITTLE HIGHER ACROSS THE
N. GFS/EUROPEAN IN DISAGREEMENT WITH THE FRONT ON THURSDAY WITH THE
GFS MOVING THE FRONT INTO THE AREA AND THE EUROPEAN KEEPING THE
FRONT WELL TO THE NW. MOISTURE AND INSTABILITY WILL AGAIN COMBINE
FOR A CHANCE OF SHOWERS AND STORMS. A WEAK FRONT WILL LIKELY BE IN
THE AREA ON FRIDAY WITH AT LEAST SMALL CHANCES FOR SHOWERS AND
STORMS. TEMPERATURES GENERALLY RUNNING NEAR TO ABOVE NORMAL.

BDL

AVIATION...
00Z UPDATE...
VFR CONDITIONS WILL PREDOMINATE ACROSS THE FORECAST AREA THROUGH THE
MAJORITY OF THIS FORECAST PERIOD...OUTSIDE OF AREAS OF CONVECTION.
THERE IS A CHANCE FOR SOME SCATTERED AREAS OF MVFR CEILINGS AND
VISIBILITIES BETWEEN 02Z AND 14Z...MAINLY IN AREAS THAT SEE BETTER
RAINFALL. BEST CHANCES FOR MAINLY SHOWERS TONIGHT AT THE TAF SITES
WILL BE BETWEEN 02Z AND 09Z AS A LARGE...WEAKENING...AREA OF
CONVECTION MOVES EAST OUT OF ALABAMA. ISOLATED THUNDERSTORMS ARE
POSSIBLE WITH THIS AREA. BETTER CHANCES FOR THUNDER WILL BE AFTER
16Z SATURDAY. WINDS WILL BE FAIRLY LIGHT AND VARIABLE THROUGH 14Z...
BUT WILL FAVOR SOUTHWEST TO SOUTHEAST. SOUTHWEST WINDS WILL INCREASE
TO 6-10KT AFTER 16Z.

//ATL CONFIDENCE...00Z UPDATE...
MEDIUM CONFIDENCE ON ALL ELEMENTS.

20

&&

.AVIATION...
06Z UPDATE...
SHOWERS AND A FEW EMBEDDED TSTORMS WORKING EAST OUT OF AL INTO GA
TONIGHT. TIME OF ARRIVAL ON MAIN CELLS FOR ATLANTA AREA SITES
BETWEEN 07Z AND 08Z BUT AM NOT CONFIDENT THEY WILL HOLD TOGETHER
AS AIRMASS IS A LITTLE MORE STABLE ACROSS GA. THIS IS EVIDENT IN THE
LARGER CELL WEST OF CSG WHICH HAS BEEN WEAKENING AS IT MOVES EAST.
DID INCLUDE TSRA IN A TEMPO GROUP AT ATL OVERNIGHT FOR SOME OF THE
STRONGER CELLS. HRRR AND HIGH RES MODELS CONTINUE TO SHOW THE EAST WEST
BANDING OF STORMS THROUGH MID MORNING BUT PRIMARILY OVER AL AND
EXTREME WESTERN GA. WILL NEED TO MONITOR THIS FOR ANY SLIGHT
EASTWARD EXTENSION AND THE NEED TO AMD WITH THUNDER.
OTHERWISE...BELIEVE CLOUD DEBRIS WILL HAMPER EARLY TS DEVELOPMENT
ON SAT BUT STILL THINK TSTORMS WILL DEVELOP IN THE AFTERNOON
PARTICULARLY ACROSS NORTH GA. MVFR CIGS AND VSBYS ARE POSSIBLE
OVERNIGHT PARTICULARLY IN SHOWERS MAINLY BETWEEN 08Z AND 12Z AND
WINDS ARE EXPECTED TO REMAIN GENERALLY LIGHT OUT OF THE SOUTHWEST
BUT INCREASING TO AROUND 10KTS AFTER 16Z.

//ATL CONFIDENCE...06Z UPDATE...
MEDIUM CONFIDENCE ON ALL ELEMENTS

30

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          82  64  82  66 /  60  60  60  40
ATLANTA         81  65  82  68 /  70  70  60  30
BLAIRSVILLE     73  57  78  60 /  70  70  70  50
CARTERSVILLE    80  64  82  66 /  70  70  60  20
COLUMBUS        85  67  86  67 /  50  50  30  20
GAINESVILLE     79  64  80  66 /  70  70  60  40
MACON           84  64  85  66 /  50  50  50  30
ROME            80  64  83  66 /  70  70  60  20
PEACHTREE CITY  80  63  84  64 /  60  60  50  20
VIDALIA         87  67  86  68 /  40  40  50  40

&&

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

$$

SHORT TERM...30
LONG TERM....NLISTEMAA
AVIATION...NLISTEMAA