
000
FXUS62 KFFC 212248 AAA
AFDFFC
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
540 PM EST TUE DEC 21 2004
.SYNOPSIS...A PATTERN CHANGE IS ON THE WAY AGAIN. THE PATTERN CHANGE FROM EARLY DECEMBER WHICH DEVELOPED AN UPPER LEVEL TROUGH IN THE CENTRAL AND EASTERN U.S. WITH A RIDGE JUST OFF THE WEST COAST WILL FLIP FLOP NEXT 7 TO 10 DAYS. IT LOOKS LIKE THIS PATTERN WE ARE IN NOW WILL END ON THE SHORT END OF THE TYPICAL 21 TO 70 DAY OSCILLATION CYCLE. HOWEVER...THE NEXT PATTERN WILL CENTER RIDGING TO OUR WEST STILL SO WITH CONFLUENT FLOW IN NE...SOME SURFACE WEDGING WILL OCCUR FROM TIME TO TIME. OVERALL...IT LOOKS LIKE WE WILL TRANSITION FROM A MEAN 3-WAVE PATTERN TO A 4 OR 5 WAVE HEMISPHERIC PATTERN. THE RESULT SHOULD BE NOT AS COLD FOR THE FIRST PART OF THE NEW YEAR WITH AN INCREASE IN STORM SYSTEMS IN WESTERLIES.
.SHORT TERM...BEFORE WE GET TO THE PATTERN CHANGE...WE MUST DEAL WITH ANOTHER POTENT STORM SYSTEM FOLLOWED BY ANOTHER SURGE OF VERY COLD ARCTIC AIR. CLOUDS WILL BE ON THE INCREASE TONIGHT AS WAA BEGINS. STRONG WAA AND ISENTROPIC UPGLIDE WILL BE ONGOING WEDNESDAY INTO WEDNESDAY EVENING AS POTENT MID LEVEL SYSTEM APPROACHES. THIS MEANS CONDITIONS WILL BE DETERIORATING AND CLOUDS LOWER AND RAIN BEGINS BY AFTERNOON. WITH EASTERLY FLOW AND SOME WEDGING...EXPECT SURFACE TEMPS WEDNESDAY WILL BE HELD DOWN AT OR BELOW GUIDANCE.
INSTABILITY IS RATHER MARGINAL AS POTENT 850 JET NEAR 60 KTS PUSHES ACROSS CWA WEDNESDAY NIGHT...BUT SHOWALTER NEARS 0C SO WILL MENTION THUNDER WEDNESDAY NIGHT ONLY. MAIN THREAT WILL BE LOCALLY HEAVY RAIN IN NORTH GEORGIA WEDNESDAY NIGHT AS STRONG WAA COMBINES WITH MAXIMIZED PE VALUES OF GREATER THAN 1.2 INCHES. THIS WILL RESULTS IN AN AREA OF RAINFALL FROM 1 TO 2 INCHES WITH LOCALIZED 3 INCH TOTALS IN FAR NW. WILL ISSUE A FLOOD WATCH FOR FAR NORTH GA AS IT HAS BEEN VERY WET THERE LATELY.
ONCE FRONT AND SYSTEM PASSES THURSDAY...EXPECT FALLING TEMPS WITH GRADUAL CLEARING WITH WINDY CONDITIONS. WILL MAKE SOME TEMPERATURE CHANGES FROM GUIDANCE WEDNESDAY NIGHT AND THURSDAY TO DEAL WITH FAST CHANGING PATTERN.
WINDY AND VERY COLD WEATHER EXPECTED CHRISTMAS EVE. A WEAK SYSTEM WILL SHEAR SOUTH OF THE AREA LATE CHRISTMAS EVE WHICH MAY PRODUCE SOME FLURRIES...ICE PELLETS...OR SPRINKLES IN MIDDLE GEORGIA AND SOUTH AS WE WILL BE IN FAVORABLE RIGHT REAR QUAD OF 300 MB JET. HOWEVER. DO NOT EXPECT MUCH OF A BIG DEAL WITH IT.
OTHER CONCERN BY FRIDAY AND FRIDAY NIGHT WILL BE WIND CHILLS. WITH WINDS STAYING UP AROUND 10 KTS FRIDAY NIGHT AND LOW LEVEL THICKNESSES SUPPORTING LOWS IN THE TEENS NORTH TO 20S MIDDLE GEORGIA...EXPECT WIND CHILLS WILL NEAR 0 IN NORTH GEORGIA WHICH WILL APPROACH WIND CHILL ADVISORY CRITERIA.
.LONG TERM...
TEMPERATURES WILL BOTTOM OUT CHRISTMAS DAY WITH 1000/850 THICKNESSES SUPPORTING MAXES ABOUT THE SAME AS YESTERDAY. HENCE...30S NORTH TO 40S SOUTH.
TEMPERATURES WILL BEGIN A SLOW WARMING TREND SUNDAY INTO NEXT WEEK WITH TEMPS RETURNING TO NORMAL NEXT WEEK. ONE QUESTION MARK WILL BE MONDAY. GFS/ECWMF TAKE CUTOFF LOW AND BRING IT ACROSS AREA MONDAY.
TELECONNECTIONS AND WAVE PATTERN THEORY SUPPORTS MORE OF A SHEARED OUT SYSTEM SO WILL FOLLOW UNITED KINGDOM UNIFIED MODEL AND CANADIAN MODEL WHICH BRINGS SOME CLOUDS BUT KEEPS PRECIP TO OUR SOUTH FOR NOW.
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.HYDROLOGY...SOME STREAMS AND RIVERS WILL NEAR OR TOP THEIR BANKS WITH SOME MINOR FLOODING IN NW GEORGIA WEDNESDAY NIGHT AND BEYOND DUE TO 1 TO 2 INCH RAIN TOTALS WITH LOCALIZED 3 INCH TOTALS. 6 TO 12 HOUR RUNOFF RATES WILL BE HIGHER THAN NORMAL AS LOCALLY HEAVY RAIN WILL OCCUR IN A SHORT AMOUNT OF TIME YIELDED 12 HOUR RAIN TOTALS BUT 6 HOUR RUNOFF RATES. FLASH FLOOD GUIDANCE NEAR 2 INCHES FOR 6 TO 12 HOURS SUPPORTS WATCH. THEREFORE...A FLOOD WATCH WILL BE ISSUED IN THE FAR NORTH AND NORTHWEST FOR WEDNESDAY NIGHT.
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.AVIATION...VFR CONDITIONS WILL COME TO AN END THIS TAF SET WITH ANOTHER ARCTIC FRONT AND POTENT UPPER-LEVEL SYSTEM ON THE WAY. EXPECT VFR CONDITIONS TO CONTINUE UNTIL LATE TONIGHT...THEN DETORIATE RAPIDLY DURING THE MID-LATE MORNING WED AND INTO THE AFTERNOON. THERE IS ALSO THE POTENTIAL FOR TSRA AND A SQUALL LINE WITH GUSTY WINDS AROUND MIDNIGHT WEDNESDAY NIGHT. COLDER...YET BETTER AVIATION CONDITIONS WILL RETURN LATE THU THROUGH THE CHRISTMAS WEEKEND.
CEILINGS...VFR CIGS SHOULD CONTINUE UNTIL AROUND OR SHORTLY AFTER 12Z. AIR MASS COLUMN REMAINS VERY DRY FROM THE SFC ON UP AND DRY AIR WILL BE SLOW TO RETREAT. AFT 12Z...EXPECT CIGS TO LOWER QUICKLY WITH WEAK WEDGE IN PLACE AND POTENTIALLY ENHANCED FROM DEVELOPING MID-LEVEL PRECIPITATION. EXPECT MVFR CIGS TO DEVELOP IN THE 12Z-15Z PERIOD...WITH IFR CIGS POTENTIALLY IN PLACE BY MID TO LATER AFTERNOON AS PCPN BEGINS TO DEVELOP.
VISIBILITY...AS NOTED ABOVE...SFC AIR MASS IS STILL VERY DRY...SO NO DEVELOPMENT OF FOG EXPECTED TONIGHT. VFR VISIBILITY CONDITIONS SHOULD CONTINUE UNTIL WED AFTERNOON...EVEN THOUGH CIGS WILL BE LOWERING. EXPECT VISIBILITY TO LOWER TO MOSTLY MVFR IN RA/SHRA AFTER 18Z WED.
WX...NONE OF SIGNIFICANCE EXPECTED UNTIL WED AFTERNOON WHEN
OVERRUNNING/ISENTROPIC RAIN SHOULD SPREAD OVER THE AREA. BEST CHANCE FOR SIGNIFICANT AND PROLONGED RAIN WITH LOWER CIGS/VSBYS WILL BE NORTH OF ATL-AHN THROUGHOUT THE AFTERNOON WED.
PRECIPITATION CHANCES WILL CULMINATE WITH A POSSIBLE SQUALL LINE OF SHRA AND ISOLD TSRA AROUND 06Z WED. GUSTY WINDS WILL BE THE MAIN PROBLEM WITH THIS SYSTEM.
WINDS...MODERATING ARCTIC SFC HIGH...WHICH WAS SOUTH OF THE AREA TODAY...NOW RELOCATING TO THE EAST OF THE AREA. WINDS NEAR 180 AT MOST SITES NOW...BUT WILL TRANSITION TO SE-E OVERNIGHT AND EARLY WED. THIS ALSO HINTS AT A WEAK WEDGE AS NOTED ABOVE. SPEEDS SHOULD REMAIN AROUND 5KTS OR LESS OVERNIGHT...THEN 5-10KTS WED. LOOK FOR GUSTY WINDS ON THE ORDER OF 25-30KTS POSSIBLY 35KTS WITH SQUALL LINE OF SHRA 06Z-09Z THU.
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.PRELIMINARY POINT TEMPS/POPS...
ATLANTA 38 54 49 49 / 10 70 99 20
ATHENS 34 53 53 54 / 00 50 99 50
GAINESVILLE 38 47 47 49 / 10 70 99 20
ROME 38 55 45 45 / 10 80 99 20
COLUMBUS 41 62 52 53 / 00 70 99 20
MACON 36 61 57 58 / 00 30 99 50
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.FFC WATCHES/WARNINGS/ADVISORIES...FLOOD WATCH FAR NORTH AND NORTHWEST GEORGIA FOR WEDNESDAY NIGHT.
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