Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 220224 AAB
AFDFFC

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
924 PM EST SUN DEC 21 2014

.UPDATE...

A FEW MINOR ADJUSTMENTS MADE TO THE SHORT TERM FORECAST GRIDS...
MAINLY CONCERNING TEMPERATURE TRENDS THIS EVENING AND A SMALL
ADJUSTMENT TO THE OVERNIGHT LOWS. OTHERWISE THE CURRENT GRIDS REMAIN
ON TRACK AS BETTER PRECIPITATION COVERAGE PUSHES EAST OF THE AREA.
WEDGE STRENGTHENS OVERNIGHT WITH AMPLE LOW-LEVEL MOISTURE FOR SOME
SCATTERED LIGHT PRECIPITATION.

20

&&

.PREV DISCUSSION... /ISSUED 625 PM EST SUN DEC 21 2014/

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
DRIZZLY AND DREARY SHORT-TERM IN STORE FOR NORTH AND CENTRAL
GEORGIA...AND WILL GIVE WAY TO A MUCH MORE ACTIVE EXTENDED.
PROLONGED STRONG ISENTROPIC LIFT WILL PREVAIL THROUGH THE SHORT-TERM
PERIOD UNDER SOUTHWEST FLOW ALOFT TO BEGIN THE PERIOD. SURFACE HIGH
IN SOUTHEAST CANADA HAS BEGUN TO RIDGE DOWN THE EASTERN SEABOARD IN
DIABATICALLY-ENHANCED CLASSICAL CAD ONSET...WITH DAMMING BECOMING
FIRMLY ENTRENCHED OVERNIGHT TONIGHT. WIDESPREAD LOW CLOUDS WILL
CONTINUE WITH DRIZZLE AND LIGHT RAIN EXPANDING NORTH WITH THE
INTRUSION OF GULF MOISTURE OVER THE COLD /WELL...COOL/ DOME TONIGHT.
BEST RAIN CHANCES WILL REMAIN ON THE SOUTH AND EAST SIDE OF THE
FORECAST AREA...HAVE GONE CATEGORICAL IN THESE AREAS FOR A HIGH-POP
LOW-QPF SITUATION...BUT DRIZZLE WILL BE POSSIBLE JUST ABOUT ANYWHERE
WITH LOW-LEVEL SATURATION UNDER THE STRENGTHENING INVERSION.

POPS LOWER SOMEWHAT ON MONDAY AS FIRST WAVE OF GULF MOISTURE EXITS
BUT DEEPENING WAVE OVER THE PLAINS WILL BRING ANOTHER ROUND OF MORE
SIGNIFICANT MOISTURE LATE INTO THE DAY INTO MONDAY NIGHT. UPPER
DIFFLUENCE WILL ADD SYNOPTIC LIFT BUT DAMMING REMAINS FIRM AT LEAST
IN THE NORTHERN HALF OF THE AREA. SHOULD SEE ENOUGH LIFTING OF THE
WARM/WEDGE FRONT TO ALLOW PORTIONS OF CENTRAL GEORGIA TO WORK INTO
THE WARM SECTOR STARTING LATE MONDAY. HIGH TEMPS MONDAY AFTERNOON
WILL BE EXTREMELY DEPENDENT ON HOW FAR THE WEDGE FRONT MAKES IT...
BUT FOR NOW HAVE TEMPS BELOW NORMAL FOR NORTHERN 2/3 OF THE AREA BUT
NEAR TO PERHAPS SLIGHTLY ABOVE EXTREME SOUTH. THIS WILL OBVIOUSLY
HAVE TO BE REEVALUATED TONIGHT TO GET A BETTER HANDLE ON LOCATION OF
THE WEDGE FRONT...BUT OBVIOUSLY SOME BUST POTENTIAL THERE.

ALL GUIDANCE KEEPS SBCAPE VALUES PRETTY MUCH 0...BUT MUCAPE VALUES
DO INCREASE LATE MONDAY NIGHT ACROSS CENTRAL GEORGIA...EXPANDING
NORTH WITH THE WARM AIR ADVECTION ALOFT. MUCAPE VALUES OF BETWEEN
200-300 J/KG SPREAD TOWARD THE METRO AREA TOWARD EARLY TUESDAY
MORNING. HAVE ADDED ISOLATED THUNDER EXTREME SOUTH TOWARD THE END OF
THE PERIOD. WANT TO REITERATE THAT AGAIN THIS IS NOT SURFACE-BASED
CAPE SO BASICALLY ONLY EXPECT ISOLATED RUMBLES EMBEDDED WITHIN THE
LARGER INCREASING RAIN SHIELD.

BY THE END OF THE PERIOD...DEEP PLAINS TROUGH HAS CUTOFF IN TO A MID-
LEVEL LOW WITH PRIMARY SURFACE LOW IN THE UPPER MIDWEST BUT
SECONDARY SURFACE LOW DEVELOPING OFF THE TEXAS GULF COAST...WITH
SOUTHWEST FLOW ALOFT OVER THE SOUTHEAST AND CONTINUED UPPER-LEVEL
DIFFLUENCE. POPS INCREASE AGAIN RAPIDLY LATE OVERNIGHT TUESDAY NIGHT
INTO EARLY WEDNESDAY MORNING...WITH SOME ACTIVE WEATHER EXPECTED
INTO THE EXTENDED. SEE BELOW.

TDP

LONG TERM /TUESDAY THROUGH SUNDAY/...
MODELS IN MORE AGREEMENT WITHIN THEMSELVES THAN PREVIOUS RUNS AND
HAVE THEREFORE MADE A FEW CHANGES TO THE TUESDAY/WEDNESDAY STORM
BASED ON THE LATEST DATA. HAVE INCREASED POPS TUESDAY INTO
WEDNESDAY. THE FOCUS FOR SEVERE WEATHER WILL BE IN TWO WAVES. THE
FIRST ON TUESDAY AS INSTABILITY INCREASES ACROSS CENTRAL GA SOUTH OF
THE WARM FRONT AND FEEL THIS WILL BE THE AREA OF CONCERN TUESDAY.
NORTH GA WILL BE IN THE COLD DOME ON TUESDAY AND ALTHOUGH THERE IS
PLENTY OF ISENTROPIC LIFT AND WHILE THERE COULD BE A FEW RUMBLES OF
THUNDER...THE COLD DOME SHOULD KEEP NORTH GA OUT OF THE SEVERE
WEATHER THREAT. THE SECOND WAVE WILL BE WITH THE COLD FRONT...MOVING
INTO THE WESTERN PART OF THE CWA WEDNESDAY MORNING. EXPECT A LINE OF
TRW...MAINLY A QLCS WITH ISOLATED TORNADOES/DAMAGING WINDS. THIS
LINE SHOULD MOVE RAPIDLY ACROSS THE CWA WEDNESDAY AS WILL THE THREAT
OF SEVERE STORMS. THE FRONT/STORMS WILL BE OUT OF THE CWA BY 00Z
THU. WITH A MORE PROMINENT WEDGE TUESDAY...HAVE MADE ADJUSTMENTS TO
MAX TEMPS TUESDAY. MODELS ARE NOW ADVERTISING A DRIER SYSTEM FOR
NEXT WEEKEND AND HAVE BROUGHT DOWN THE POPS JUST A LITTLE. NO OTHER
CHANGES ARE PLANNED TO THE LONG TERM.

17

AVIATION...
00Z UPDATE...

MOST AREAS MVFR CURRENTLY WITH LOCAL IFR OR LOWER ACROSS CENTRAL
GEORGIA. I EXPECT WIDESPREAD IFR CONDITIONS BY 06Z WITH PREDOMINANT
LIFR CONDITIONS BY 10Z. MOST AREAS IMPROVE ONCE AGAIN TO IFR OR MVFR
BY 18Z. PORTIONS OF FAR NORTH GEORGIA WILL LIKELY REMAIN IFR TO MVFR
THROUGH THE PERIOD. AREAS OF LIGHT RAIN ARE EXPECTED TO SPREAD
NORTH...BECOMING WIDESPREAD ACROSS EASTERN PORTIONS OF THE AREA 06Z-
12Z...REMAINING ISOLATED TO SCATTERED ELSEWHERE. EAST WINDS 3-8KT
THROUGH THE PERIOD.

//ATL CONFIDENCE...00Z UPDATE...

MEDIUM TO HIGH.

20

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          40  48  43  48 /  70  60  60 100
ATLANTA         41  51  45  52 /  40  40  50 100
BLAIRSVILLE     38  49  42  48 /  60  50  50 100
CARTERSVILLE    40  52  45  50 /  30  30  40 100
COLUMBUS        43  58  52  65 /  50  40  50 100
GAINESVILLE     39  48  42  46 /  60  50  60 100
MACON           43  54  49  63 /  70  50  50 100
ROME            40  53  46  54 /  30  30  40 100
PEACHTREE CITY  40  52  46  56 /  40  40  50 100
VIDALIA         44  57  52  71 /  80  70  50 100

&&

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

$$

SHORT TERM...20
LONG TERM....NLISTEMAA
AVIATION...20



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