Area Forecast Discussion
Issued by NWS Atlanta, GA

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000
FXUS62 KFFC 180804
AFDFFC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
404 AM EDT SAT APR 18 2015

.SHORT TERM /TODAY THROUGH SUNDAY/...

ALTHOUGH MEDIUM RANGE AND HI-RES MODELS ARE POINTING TO A RELATIVE
MINIMUM FOR PRECIPITATION TODAY AS WEAK UPPER RIDGING TAKES PLACE...
AMPLE MOISTURE REMAINS IN PLACE OVER THE REGION. BETTER RAIN HAS
MOVED OFF TO THE EAST...BUT SCATTERED SHOWERS AND AREAS OF DRIZZLE
PERSIST EARLY THIS MORNING. WILL KEEP SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS IN THE FORECAST DURING THE DAY TODAY. INSTABILITY IS
MARGINAL THROUGH THE DAYTIME PERIOD AND SEVERE THREAT IS MINIMAL.
MUCH BETTER RAIN CHANCES SPREAD ACROSS TONIGHT THROUGH SUNDAY AS THE
CLOSED UPPER LOW OVER THE SOUTHERN ROCKIES FINALLY OPENING UP AND
KICKING EAST. INSTABILITY TONIGHT REMAINS FAIRLY LOW...BUT SHEAR IS
INCREASING...MAY SEE SOME MARGINAL SEVERE THREAT INTO THE WESTERN
PORTION OF THE FORECAST AREA AFTER MIDNIGHT. MODERATE INSTABILITY...
SHEAR AND DYNAMICS SUNDAY WILL UP THE SEVERE THREAT TO AT LEAST
MARGINAL...APPROACHING SLIGHT. AREA SOILS ARE AT OR NEAR SATURATION
AND PRECIPITABLE WATER VALUES REMAIN WELL ABOVE SEASONAL NORMALS.
FORECAST RAINFALL AMOUNTS MAY PRODUCE SOME ISOLATED MINOR FLOODING
BUT COVERAGE IS EXPECTED TO REMAIN A BIT LIMITED FOR A FLOOD WATCH
AT THIS TIME.

20


.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...

LONG TERM PERIOD BEGINS WITH A LULL IN ACTIVITY AS SHORTWAVE MOVES
EAST OF THE AREA BUT STRONGER SHORTWAVE AND ATTENDANT COLD FRONT
REMAIN WELL WEST OF THE AREA AS 00Z MON. TRANSLATIONAL SPEED OF
THESE FEATURES HOWEVER WILL BE VERY RAPID TO THE EAST AND EXPECT
SHOWERS AND THUNDERSTORMS TO MOVE INTO THE NORTHWEST ZONES PRIOR
TO 06Z. INTO SUNDAY NIGHT...ANTICIPATE HIGH SHEAR ENVIRONMENT WITH
50 KT 850 JET AND 400 M2/S2 LOW LEVEL HELICITY. INSTABILITY WILL
BE A LITTLE HARDER TO COME BY AND MOST UNSTABLE AIR WILL REMAIN
OUTSIDE OF THOSE AREAS WITH THE HIGHEST SHEAR. DESPITE
THIS...ANTICIPATE ENOUGH ENERGY TO ALLOW FOR STRONG TO SEVERE
THUNDERSTORM DEVELOPMENT ACROSS THE NORTHERN TIER WITH WINDS THE
MAIN CONCERN BUT ISOLATED TORNADOES NOT OUT OF THE QUESTION
EITHER.

INTERESTING SPIKE IN INSTABILITY OVER SOUTHEAST CORNER OF THE
FORECAST AREA MONDAY AFTERNOON WITH STILL ENOUGH LOW LEVEL WINDS
AND SHEAR AROUND TO WARRANT CONCERN OVER ADDITIONAL STRONG TO
SEVERE STORMS. CAPE VALUES MAX OUT IN THE 2000 TO AS HIGH AS 2500
J/KG RANGE FROM COLUMBUS TO MACON TO ATHENS SHIFTING QUICKLY OUT
OF THE AREA BY 00Z. NAM12 STP VALUES PICK UP IN THIS WITH VALUES
CLOSE TO 5 DURING THE PEAK TIME MONDAY AFTERNOON.

FINALLY SOME DRYING OUT MONDAY NIGHT AND ESPECIALLY INTO TUESDAY
AS HIGH PRESSURE BUILDS IN WEST OF THE AREA. SHOULD BE LARGELY A
GOOD DAY ON WEDNESDAY AS WELL ALTHOUGH THE GFS IS MORE AGGRESSIVE
IN BRINGING MOISTURE ASSOCIATED WITH EMBEDDED SHORTWAVES IN WNW
FLOW ALOFT THAN THE ECMWF. WENT WITH A COMPROMISE FOR NOW WHICH
INDICATES LOW END CHANCE POPS FOR THE EXTREME NORTH WEDNESDAY
AFTERNOON. NEXT MAJOR SYSTEM LOOKS TO BE LATE NEXT FRIDAY INTO
SATURDAY WITH DECENT AGREEMENT THIS FAR OUT BETWEEN THE GFS AND
EURO AND WILL INDICATE HIGH END CHANCE POPS FOR NOW.

DEESE


&&

.AVIATION...
06Z UPDATE...

MOST AREAS ALREADY DOWN INTO THE IFR OR LOWER RANGE AT THIS TIME AND
I EXPECT IFR OR LOWER CONDITIONS TO PREDOMINATE THROUGH 16Z. MOST
AREAS SHOULD IMPROVE TO MVFR CONDITIONS BY 18Z WITH AREAS OF IFR
CONDITIONS POSSIBLE BETWEEN 20Z AND 02Z. MOST AREAS WILL BACK DOWN
TO IFR OR LOWER CONDITIONS BY 06Z. LARGE AREA OF MODERATE TO
OCCASIONALLY HEAVY RAIN EXITING THE FORECAST AREA TO THE EAST AT
THIS TIME. PATCHY AREAS OF LIGHT RAIN OR DRIZZLE ARE EXPECTED
THROUGH 14Z. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE
EXPECTED ACROSS THE AREA THIS AFTERNOON...GENERALLY BETWEEN 18Z AND
00Z. AFTER 00Z A LARGE AREA OF WIDESPREAD RAIN AND SHOWERS WILL
SPREAD ACROSS THE AREA BETWEEN 00Z AND 06Z. WINDS WILL BE NORTHEAST
TO SOUTHEAST THROUGH THE PERIOD...GENERALLY BETWEEN 4-8KTS.

//ATL CONFIDENCE...06Z UPDATE...

MEDIUM TO HIGH.

20

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          77  63  73  63 /  40  80  80  60
ATLANTA         76  64  74  64 /  50  80  80  50
BLAIRSVILLE     74  59  69  58 /  40  80  80  60
CARTERSVILLE    76  63  75  62 /  50  80  80  50
COLUMBUS        78  66  76  64 /  50  80  80  40
GAINESVILLE     75  62  71  62 /  40  80  80  60
MACON           78  65  76  63 /  40  80  80  50
ROME            77  63  74  62 /  50  80  80  50
PEACHTREE CITY  76  64  74  63 /  50  80  80  40
VIDALIA         79  67  77  64 /  40  70  80  50

&&

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

$$

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


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