Area Forecast Discussion
Issued by NWS Atlanta, GA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KFFC 211739 AFDFFC AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PEACHTREE CITY GA 1239 PM EST FRI NOV 21 2014 .PREV DISCUSSION... /ISSUED 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... 18Z UPDATE... VFR CONDITIONS WILL CONTINUE THIS AFTERNOON AND EVENING AS WINDS BECOMING NORTHEAST AROUND 5KTS OR LESS. MOISTURE INCREASES LATE TONIGHT BRINGING MVFR CIGS INTO CSG/MCN BY 10-12Z...AND INTO ATL BY SATURDAY AFTERNOON. WINDS WILL REMAIN ON THE EAST SIDE TONIGHT AND SATURDAY ALTHOUGH SPEEDS WILL BE NEAR CALM TONIGHT AND 5 TO 10 KTS SATURDAY. //ATL CONFIDENCE...18Z UPDATE... HIGH ON ALL ELEMENTS. 17 && .PRELIMINARY POINT TEMPS/POPS... ATHENS 59 34 54 43 / 0 0 5 90 ATLANTA 60 38 56 46 / 0 0 5 100 BLAIRSVILLE 56 30 55 39 / 0 0 5 90 CARTERSVILLE 57 34 57 44 / 0 0 5 90 COLUMBUS 63 40 62 52 / 0 0 5 100 GAINESVILLE 58 35 52 43 / 0 0 5 90 MACON 64 36 63 51 / 0 0 5 100 ROME 58 34 59 45 / 0 0 5 90 PEACHTREE CITY 60 34 56 47 / 0 0 5 100 VIDALIA 64 41 65 55 / 0 0 5 100 && .FFC WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...17 LONG TERM....11 AVIATION...17

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.