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Area Forecast Discussion

531
FXUS62 KFFC 271913
AFDFFC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
313 PM EDT MON APR 27 2015

.SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...

LATEST REGIONAL SURFACE ANALYSIS SHOWS SEVERAL BOUNDARIES OF NOTE
WITH THE MAIN BEING THE OLD FRONTAL BOUNDARY ANALYZED FROM THE
GULF COAST THROUGH CENTRAL FLORIDA. DEWPOINT BOUNDARY HOWEVER IS
CONSIDERABLY FURTHER NORTH INDICATED BY A SUBTLE TROUGH AND
ROUGHLY ALONG AND SOUTH OF A CSG TO MCN LINE. DEWPOINTS IN THE 30S
CURRENTLY FOR NORTH GEORGIA AND IN THE MID 50S SOUTH OF THIS
FEATURE.

FOR TONIGHT...LOW PRESSURE WILL BEGIN TO DEVELOP ALONG THIS FRONT
OVER THE NORTHERN GULF OF MEXICO AS CLOSED UPPER LOW MOVES SLOWLY
EAST OUT OF TEXAS. THIS WILL ALLOW FOR AND ISENTROPIC UPGLIDE
SETUP TO DEVELOP LOCALLY WITH INCREASED MID LEVEL CLOUDS INITIALLY
DECREASING TO SOME LOWER CIGS FOR THE SOUTHWEST PORTIONS OF THE
FORECAST AREA LATE TONIGHT. THIS WILL CORRESPOND TO AN INCREASE IN
LIGHT RAIN DEVELOPMENT FOR THESE SAME AREAS AND WILL KEEP CHANCE
POPS IN THROUGH TUESDAY MORNING.

DEVELOPING DIFFLUENT FLOW ALOFT WILL ACT IN TANDEM WITH
STRENGTHENING ISENTROPIC ASCENT TO INCREASE RAIN CHANCES RAPIDLY
LATE TUESDAY AFTERNOON THROUGH THE EVENING HOURS. HAVE RAMPED UP
POPS EVEN FURTHER AND NOW HAVE A SMALL AREA OF CATEGORICAL FOR
WEST CENTRAL GEORGIA PORTIONS LATE TUESDAY. INSTABILITY WILL BE
LIMITED BUT NAM12 DOES INDICATE MARGINAL VALUES ENCROACHING UPON
THE FAR SOUTHERN SECTIONS AND WILL GO WITH ISOLATED THUNDER
THROUGH THE REMAINDER OF THE SHORT TERM PERIOD.

AS UPPER LOW TRACKS ACROSS NORTHERN ALABAMA...DYNAMICS ARE PRETTY
MUCH MAXIMIZED FOR THIS EVENT TUESDAY NIGHT AND HAVE GONE
CATEGORICAL FOR ALL AREAS WITH ISOLATED THUNDER FOR THE SAME AREAS
MENTIONED BEFORE.

DEESE


.LONG TERM /WEDNESDAY THROUGH MONDAY/...

MADE A FEW ADJUSTMENTS TO THE EXTENDED FORECAST GRIDS...MAINLY IN THE
FIRST FEW PERIODS. ADJUSTED POPS A BIT AND ALSO ADJUSTED AREA FOR
THUNDER WEDNESDAY TO MATCH LATEST MODEL TRENDS. ADDED THUNDER TO THE
THURSDAY/THURSDAY EVENING PERIOD AS WELL. INSTABILITY IS FORECAST TO
BE MARGINAL...HOWEVER STEEP LAPSE RATES INDICATE SHALLOW CONVECTION
IS LIKELY TO CONTAIN FAIRLY VIGOROUS UPDRAFT POTENTIAL. OTHERWISE
MINIMAL CHANGES MADE TO THE REMAINDER OF THE EXTENDED FORECAST
PERIOD. PLEASE SEE THE PREVIOUS EXTENDED FORECAST DISCUSSION BELOW.

20


PREVIOUS LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

STILL ONE MAIN SYSTEM TO FOCUS ON FOR THE LONG TERM. CLOSED UPPER
LEVEL LOW SLIDES FROM THE MISSISSIPPI VALLEY INTO THE TENNESSEE
VALLEY TUESDAY NIGHT WHILE THE SFC LOW SLIDES ALONG THE GULF COAST.
THIS SHOULD RESULT IN RAIN SPREADING ACROSS THE CWA AT THE BEGINNING
OF THE LONG TERM AND TUESDAY NIGHT AND WEDNESDAY STILL LOOK TO BE THE
MOST LIKELY TIME PERIOD FOR PRECIPITATION. AS THE SFC LOW TRACKS INTO
THE ATLANTIC...RAIN SHOULD END BY FRIDAY. THERE STILL REMAIN SOME
DIFFERENCES IN HOW THE ECMWF AND THE GFS ARE RESOLVING FEATURES WITH
THIS SYSTEM /ESPECIALLY IN TERMS OF THE SFC LOW TRACK ONCE IT MOVES
INTO THAT ATLANTIC AND THE UPPER LEVEL SHORTWAVE AS IT TRACKS ACROSS
THE EAST/ BUT THE MAJORITY OF THE TIME THE TWO MODELS ARE IN DECENT
AGREEMENT ON THE WEATHER IMPACTS FOR THE CWA. INSTABILITY VALUES ARE
A LITTLE BIT HIGHER THAN HAVE BEEN NOTED IN PREVIOUS RUNS WITH MUCAPE
VALUES EXCEEDING 1000 J/KG ON WEDNESDAY AFTERNOON. IN ADDITION...THE
HIGHER VALUES SPREAD FURTHER NORTHWARD. WITH THIS FORECAST HAVE
INCLUDED THAN MENTION OF THUNDERSTORMS FURTHER NORTHWARD /INTO THE
SOUTHERN AND WESTERN PORTIONS OF THE ATL METRO AREA/ COMPARED TO THE
PREVIOUS FORECAST.

HIGH PRESSURE BUILDS IN FOR THE WEEKEND...ALLOWING FOR DRY
CONDITIONS ACROSS THE CWA.

11

&&

AVIATION...
18Z UPDATE...
MVFR HAS LIFTED ACROSS ALL TAF SITES WHICH WERE IMPACTED AND
ANTICIPATE VFR CONDITIONS FOR THE REMAINDER OF THIS TAF PERIOD.
INCREASING CHANCES FOR -RA FOR THE END OF THE TAF
PERIOD...ESPECIALLY FOR CSG BUT SHOULD STILL BE VFR. KEEPING WIND
SHIFT AT ATL AS IS AT AROUND 05Z.

//ATL CONFIDENCE...18Z UPDATE...
HIGH ON ALL ELEMENTS.

DEESE

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          50  68  51  60 /   5  40  80  80
ATLANTA         52  67  52  60 /  10  70  80  60
BLAIRSVILLE     40  65  47  57 /   5  50  80  70
CARTERSVILLE    44  68  51  60 /  10  70  80  60
COLUMBUS        55  70  57  66 /  40  60  80  60
GAINESVILLE     50  66  50  57 /   5  50  80  70
MACON           52  69  54  65 /  20  60  80  70
ROME            45  69  52  62 /  10  70  80  60
PEACHTREE CITY  47  68  52  62 /  20  70  80  60
VIDALIA         57  71  60  71 /  20  50  60  70

&&

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

$$

SHORT TERM...DEESE
LONG TERM....20
AVIATION...DEESE



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