Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 211136 AAA
AFDFFC

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE
PEACHTREE CITY GA 625 AM EST FRI NOV 21 2014


.SHORT TERM /TODAY THROUGH SATURDAY/...
WEAK UPPER RIDGING BUILDS INTO THE REGION TODAY AHEAD OF
AN INCREASING SOUTHWESTERLY UPPER FLOW PATTERN BY SATURDAY. MOSTLY
CLEAR...DRY AND MILD CONDITIONS THROUGH TONIGHT WITH INCREASING
CLOUDS BY EARLY SATURDAY. SURFACE RIDGE TRANSITS FROM THE MIDDLE
OHIO VALLEY TO THE MID-ATLANTIC COAST BY SATURDAY MORNING TURNING
THE LOW-LEVEL FLOW TO EASTERLY. BY SATURDAY...LOW-LEVEL FLOW OFF OF
THE ATLANTIC AND INCREASING OVER-RUNNING SOUTHWESTERLY FLOW IN THE
MID AND UPPER LEVELS WILL RESULT IN INCREASING CLOUDS AND SLIGHTLY
COOLER TEMPERATURES. RIGHT NOW IT APPEARS THAT PRECIPITATION WILL
HOLD OFF THROUGH THE DAY SATURDAY.

20


.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...

SATURDAY THROUGH SUNDAY...THE EXTENDED PERIOD BEGINS WITH STRONG
ISENTROPIC LIFT UNDERWAY ACROSS THE ENTIRE REGION AS A RESULT OF
THE STRONG SOUTHERLY FLOW IN THE 850-925 MB LAYER RUNNING OVERTOP
OF THE STRONG WEDGE IN PLACE AT THE SURFACE. CENTER
OF THE SURFACE RIDGE IN BOTH THE ECMWF AND GFS LOCATED JUST OF THE
NORTH CAROLINA COAST WITH A CLEAR WEDGE PATTERN NOTED IN THE
ISOBARS. RAIN SHOWERS SHOULD COMMENCE STARTING IN THE SOUTH AS
EARLY AS SAT AFTERNOON AND EARLY EVE AND SPREAD NORTH AS
CONDENSATION PRESSURE DEFICITS REDUCE TO LESS THAN 10MB...WHICH
SHOULD NOT TAKE LONG GIVEN THE 30 TO 40 KT UPGLIDE ACROSS A 100MB
SPREAD AT BOTH THE 290K AND 295K SURFACES FROM SOUTH GA TO NORTH
GA. BIGGEST FORECAST CHALLENGE IS HOW MUCH THE WEDGE WILL ERODE IN
THE FACE OF STRONG SOUTHERLY FLOW AHEAD OF THE APPROACHING STRONG
SHORT WAVE ALLOWING FOR THE SEVERE THREAT TO ADVANCE NORTH. LATEST
SPC DAY 3 GUIDANCE SHOWING A MARGINAL THREAT I.E 5 PCT AREA SUNDAY
AS FAR NORTH AS I20 AND A SLIGHT RISK FOR THE AREA ALONG AND SOUTH
OF A CSG TO MCN LINE WHERE MODELS SUGGEST INSTABILITY WILL BE
SUFFICIENT ENOUGH ALONG WITH HIGH SHEAR VALUES TO SUPPORT A
SEVERE THREAT. 0-1 KM HELICITY VALUES ARE HIGHEST IN NORTH GA
HOWEVER MODELS AGREE THAT INSTABILITY WILL BE LIMITED TO NON
EXISTENT AT THE SURFACE. MAY SEE SOME ELEVATED THUNDER ACROSS THE
NORTH GIVEN THE STRONG ISENTROPIC LIFT BUT WHERE SURFACE
INSTABILITY IS HIGH ACROSS THE AFOREMENTIONED SLIGHT RISK
REGION...0-1 HELICITY VALUES RUNNING 200-300M2/S2 AND BULK SHEAR
RUNNING AOA 50 KTS IS MORE THAN ENOUGH TO MENTION A TORNADO AND
DAMAGING WIND THREAT. NOT IMPRESSED WITH MID LEVEL LAPSE RATES
ENOUGH TO THINK HAIL AS A SEVERE RISK HOWEVER. HAVE MENTIONED
SEVERE IN THE FORECAST STARTING SUNDAY AM THROUGH EARLY AFTERNOON
GENERALLY ALONG A LA GRANGE TO MONTICELLO TO WASHINGTON LINE.
OBVIOUSLY THE FURTHER SOUTH THE HIGHER THE RISK AS INSTABILITY
INCREASES. ONE OTHER FLY IN THE OINTMENT WILL BE THE GFS
INSISTENCE THAT CONVECTION ALONG THE COAST WILL FIRE THUS CUTTING
OFF NORTHWARD MOISTURE TRANSPORT. SHOULD THAT OCCUR...WILL BE
DIFFICULT TO GET A SEVERE THREAT NORTH OF THE FALL LINE. BUT FOR NORTH
GA...WILL HAVE TO WATCH THE INLAND PUSH OF THE WARM SECTOR AS THAT
WILL DETERMINE THE THREAT AND WHETHER THE COASTAL CONVECTION
SHAPES UP. APPEARS TO BE A WINDOW FROM ABOUT 11 AM SUNDAY THROUGH
THE AFTERNOON WHERE THE WEDGE COULD ERODE ENOUGH TO ALLOW A THREAT
BUT WILL HAVE TO WATCH AS THE EVENT DRAWS NEAR.

MONDAY...TUESDAY... SURFACE FEATURE THAT MOVES THROUGH ON SUNDAY
HANGS UP ACROSS SOUTH GA AND NORTH FL. HAVE KEPT POPS IN THE
SOUTH AND SOUTHEAST AS A RESULT WHILE WE AWAIT ANOTHER WAVE
ROUNDING THE BASE OF THE MEAN TROF OVER THE CENTER OF THE COUNTRY
WHICH WILL CLEAR THE REGION OUT BY WED. AREA WILL REMAIN UNDER A
GENERAL SOUTHWEST FLOW THROUGH WED THUS KEEPING GENERAL SLIGHT
RAIN CHANCES/CLOUDS IN THE FORECAST.

WEDNESDAY...GFS AND ECMWF IN GENERAL AGREEMENT WITH THE MEAN TROF
CLEARING THE REGION ON WED WITH COOLER AIR FILTERING IN BEHIND
SETTING US UP FOR A COOL...BUT NICE THANKSGIVING HOLIDAY ON THU.

THURSDAY...FRIDAY.. NORTHWEST FLOW ALOFT AND COLD SURFACE HIGH
BUILDING IN FOR NICE WEATHER TO END THE WEEK. ECMWF A BIT DEEPER
WITH THE TROF OVER THE EAST AND A BIT MORE MOISTURE ACROSS THE
NORTH GA MOUNTAINS WHICH WOULD SUGGEST SOME FLURRIES OR SNOW
SHOWERS TYPICAL OF NORTHWEST FLOW SYSTEMS LIKE THIS. GFS NOT SO
BOLD SO WILL HAVE TO WAIT AND SEE. FOR NOW LEFT ANY MENTIONS OUT.

STELLY


&&


AVIATION...
12Z UPDATE...

VFR CONDITIONS ARE EXPECTED TO PREDOMINATE ACROSS THE FORECAST AREA
THROUGH THE PERIOD. LOCAL TO SCATTERED MVFR OR LOWER VISIBILITIES
ARE POSSIBLE AT FOG-PRONE AREAS ACROSS MAINLY CENTRAL GEORGIA
THROUGH 14Z...HOWEVER THE ONLY TAF SITE IMPACTED IS KMCN. LIGHT
NORTHWEST WINDS WILL TREND TOWARD DUE NORTH THROUGH 14-15Z...
BECOMING NORTHEAST ALL AREAS BY 18Z. WIND SPEEDS WILL BE GENERALLY
6KT OR LESS THROUGH THE PERIOD. WILL SEE SOME MVFR CEILINGS
RETURNING TO SOUTHERN PORTIONS OF THE FORECAST AREA TOWARD 12Z
SATURDAY MORNING 09-12Z.

//ATL CONFIDENCE...12Z UPDATE...
HIGH ON ALL ELEMENTS.

20

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          59  34  54  43 /   0   5   5  80
ATLANTA         60  38  56  46 /   0   5  10  80
BLAIRSVILLE     56  30  55  39 /   0   5   5  80
CARTERSVILLE    57  34  57  44 /   0   5   5  80
COLUMBUS        63  40  62  52 /   0   5  10  90
GAINESVILLE     58  35  52  43 /   0   5   5  80
MACON           64  36  63  51 /   0   5  10  80
ROME            58  34  59  45 /   0   5   5  60
PEACHTREE CITY  60  34  56  47 /   0   5  10  80
VIDALIA         64  41  65  55 /   0   5   5  80

&&

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

$$

SHORT TERM...20
LONG TERM....30
AVIATION...20



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