Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 040845
AFDFFC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
345 AM EST WED MAR 4 2015

.SHORT TERM /TODAY THROUGH THURSDAY/...
WEDGE IS ERODING ON ITS WESTERN SIDE THIS MORNING. VSBYS AND CIGS
HAVE GREATLY IMPROVED UP THE AL/GA STATE LINE...AND ESPECIALLY
WHERE WINDS HAVE TURNED SOUTHERLY OR SOUTHWESTERLY. THE FOG IS
SHALLOW...AND CIGS ARE AN OBSCURATION RATHER THAN A CLOUD DECK...SO
CLEARING WILL BE FAIRLY RAPID WHEN IT OCCURS. WILL BE MAKING
ADJUSTMENTS TO THE DENSE FOG ADVISORY WHERE VSBYS HAVE COME UP ABOVE
1/4SM. WILL LIKELY HAVE TO CLEAR ADDITIONAL ZONES BEFORE LEAVING
THIS MORNING AS CONDITIONS IMPROVE.

A COLD FRONT IS STILL ON TRACK TO IMPACT THE CWFA LATER TODAY INTO
THURSDAY. MODELS ARE IN GOOD AGREEMENT WITH THE TIMING OF THE
BOUNDARY AND KEEPING MOST OF THE PRECIP ANAFRONTAL.  IN THE LAST FEW
MODEL RUNS...THE 500MB TROUGH HAS BECOME LESS SHARP OVER THE
CWFA...AND WASHES OUT. IN ADDITION...MODELS HAVE ALSO DELAYED THE
ARRIVAL OF THE COLD AIR BEHIND THE FRONT. THE TIMING OF THE COLD AIR
AT THE SURFACE AND ALOFT IS VERY TRICKY AND MODELS HAVE DEFINITELY
STRUGGLED WITH THIS IN PREVIOUS RUNS. CURRENTLY...THE COLDEST AIR
DOESN`T BEGIN INFILTRATING THE NORTHERN CWFA UNTIL BETWEEN 12Z AND
15Z THU. IF THIS HOLD TRUE...ANY WINTRY MIX UP NORTH WILL BE MOSTLY
DURING THE DAY ON THU RATHER THAN OVERNIGHT WED. HOWEVER...REMEMBER
THAT THE MODELS CONTINUE TO STRUGGLE WITH TEMPS AT THE SURFACE AND
ALOFT...SO NOT A HIGH CONFIDENCE SITUATION FOR THE TIMING OF THE
COLD AIR.

PTYPE WILL ALSO HEAVILY DEPEND UPON THE TIMING OF THE COLD AIR. FOR
THE LAST FEW RUNS...MODEL SOUNDINGS ARE SHOWING RAIN MIXING WITH
SLEET AT TIMES AS THE COLD AIR MOVES INTO THE REGION. THEN...RAIN
MAY SWITCH OVER TO A MIXTURE OF SLEET AND FREEZING RAIN...FINALLY
FINISHING OFF WITH THE POTENTIAL FOR SOME FREEZING DRIZZLE. IF THE
COLD AIR IS DELAYED ANY FURTHER INTO THU...THEN THE POTENTIAL FOR AN
IMPACTFUL AMOUNT OF WINTRY MIX BECOMES LESS AND LESS. FOR NOW...NOT
EXPECTING MUCH SLEET ACCUMULATION...AMOUNTS SHOULD BE LESS THAN A
QUARTER OF AN INCH. DO THINK LIGHT ICING WILL BE AN ISSUE...BUT
AMOUNTS SHOULD BE A TENTH OF AN INCH OR LESS IN MOST LOCALES.
AGAIN...THE PTYPE IS HEAVILY DEPENDENT UPON THE TEMPERATURES ALOFT
AND AT THE SURFACE...SOMETHING THE MODELS HAVE BEEN STRUGGLING
WITH...SO CONFIDENCE IS LOW TO MEDIUM IN ACCUMULATIONS. THE
ACCUMULATION ISSUE WILL ALSO BE COMPLICATED BY WARM GROUND TEMPS.

TEMPS TODAY ARE EXPECTED TO BE WELL ABOVE NORMAL AND EVEN POSSIBLY
REACH THE LOWER 80S IN THE FAR SOUTH. A FEW BREAKS IN THE CLOUDS ARE
POSSIBLE ALONG AND WEST OF THE ERODING EDGE OF THE WEDGE. TEMPS ON
THURSDAY SHOULD BE NEARLY STEADY IN THE NORTH...AND SHOULD FALL
THROUGH THE AFTERNOON ELSEWHERE.

NLISTEMAA


.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
PERIOD STARTS OUT COOL BUT MOSTLY DRY AS PRECIPITATION EXITS THE
FORECAST AREA LATE IN THE DAY THURSDAY...LINGERING ONLY IN THE
SOUTHEAST INTO THURSDAY EVENING. UPPER-LEVEL AND SURFACE PATTERNS
ARE NOT TYPICAL OF SUCH A STRONG SHOT OF COLDER AIR THIS LATE IN THE
SEASON WITH NEARLY ZONAL FLOW ALOFT AND RAPIDLY WEAKENING SURFACE
PRESSURE GRADIENT...BUT UPSTREAM REGION DOES HAVE GOOD RESIDUAL SNOW
COVER. I AM INCLINED BACK OFF A LITTLE ON COLD TEMPERATURES THURSDAY
NIGHT...GENERALLY STAY CLOSER TO THE NAM MOS NUMBERS WHICH ARE STILL
WELL BELOW SEASONAL NORMALS. THE REMAINDER OF THE EXTENDED FORECAST
PERIOD IS RELATIVELY QUIET IF POTENTIALLY WET AT TIMES. UPPER FLOW IS
WEAK AND GENERALLY ZONAL THROUGH THE WEEKEND WITH WEAK SURFACE HIGH
PRESSURE OVER THE SOUTHEASTERN U.S. LARGER SCALE FEATURES REMAIN
RELATIVELY SIMILAR BETWEEN THE GFS AND ECMWF THROUGH THE MAJORITY OF
THE EXTENDED PERIOD...BUT ALSO REMAIN SOMEWHAT VAGUE ON BOTH
CONCERNING ANY ENHANCED LIFT FOR RAIN CHANCES. GFS LIFTS WEAK SHORT
WAVE THROUGH SUNDAY INTO MONDAY WHILE ECMWF DELAYS THE WEAK SHORT
WAVE UNTIL THE MONDAY-TUESDAY PERIOD. FOR NOW I DO NOT HAVE ENOUGH
CONFIDENCE IN EITHER SCENARIO TO FOCUS ON ANY SPECIFIC SOLUTION. PLAN
ON RUNNING WITH SEASONAL TEMPERATURES AND CHANCE POPS AT BEST SUNDAY
THROUGH THE END OF THE FORECAST.

20


&&

AVIATION...
06Z UPDATE...
WEDGE OF LOW CLOUDS AND FOG IS FINALLY BEGINNING TO ERODE ON THE
SOUTHWEST SIDE. MEANWHILE...THE NORTHERN TERMINAL SITES REMAIN
LOCKED IN AT 1/2SM TO 1/4SM FOG AND VLIFR CIGS. THE TRICKY PART OF
THE FORECAST WILL BE TO TIME THE EDGE OF THE CLEARING. DO THINK
WHEN THE FOG AND LOW CLOUDS CLEAR...IT WILL GO VERY VERY QUICK. MY
TIMING OF IMPROVING VSBYS AND CIGS AT ATL WILL LIKELY HAVE TO BE
ADJUSTED DEPENDING UPON THE SPEED OF CLEARING ON THE SW SIDE. EAST
WINDS WILL SWITCH AROUND TO THE S AND THEN SW QUICKLY ALSO...WENT
WITH THE RAP BECAUSE IT HELD ONTO THE WEDGE A FEW MORE HOURS THAN
THE OTHER MODELS WHICH ARE NOTORIOUS FOR CLEARING TOO SOON. COLD
FRONT WILL BEGIN TO DROP SOUTH TODAY...BRINGING AN AREA OF PRECIP.
DIDN`T ADJUST POPS FOR THIS CYCLE AS MODELS ARE IN PRETTY GOOD
AGREEMENT WITH TIMING. HOWEVER...A FEW TWEAKS MAY HAVE TO BE MADE
FOR LATER TAF ISSUANCES.

//ATL CONFIDENCE...06Z UPDATE...
MEDIUM CONFIDENCE ALL ELEMENTS.

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          72  60  62  32 /  40  80  80  10
ATLANTA         71  53  55  30 /  40  90 100  10
BLAIRSVILLE     65  45  46  26 /  70 100 100  10
CARTERSVILLE    72  42  44  26 /  60 100 100   5
COLUMBUS        76  63  64  35 /  20  80  80  10
GAINESVILLE     69  54  56  30 /  60 100 100  10
MACON           78  63  66  37 /  20  60  80  10
ROME            70  40  42  24 /  70 100 100   5
PEACHTREE CITY  73  57  58  30 /  40  90  90  10
VIDALIA         81  62  77  41 /  10  20  70  40

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR THE
FOLLOWING ZONES: BALDWIN...BANKS...BARROW...BIBB...BUTTS...
CHEROKEE...CLARKE...COBB...DAWSON...DEKALB...EMANUEL...FANNIN...
FORSYTH...GILMER...GLASCOCK...GREENE...GWINNETT...HALL...
HANCOCK...HENRY...JACKSON...JASPER...JEFFERSON...JOHNSON...
JONES...LAURENS...LUMPKIN...MADISON...MONROE...MORGAN...NEWTON...
NORTH FULTON...OCONEE...OGLETHORPE...PICKENS...PUTNAM...
ROCKDALE...TALIAFERRO...TOWNS...TREUTLEN...TWIGGS...UNION...
WALTON...WARREN...WASHINGTON...WHITE...WILKES...WILKINSON.

&&

$$

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


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