000
FXUS62 KFFC 121127
AFDFFC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
627 AM EST WED FEB 12 2014

.SHORT TERM /TODAY THROUGH THURSDAY/...
/ISSUED AT 339 AM EST WED FEB 12 2014/
WE ARE WATCHING A WINTER STORM OF HISTORICAL SIGNIFICANCE BEGINNING 
TO UNFOLD ON THE MIDNIGHT SHIFT TONIGHT. REPORTS OF SNOW AND SLEET 
ALREADY COMING IN ACROSS THE METRO AREA AS CAD WEDGE STRENGTHENS AND 
PUSHES FURTHER SOUTHEAST. SURFACE HIGH HAS JUST CROSSED THE 
APPALACHIANS SO THE AGEOSTROPHIC ADJUSTMENT IS KICKING IN...AND CAD 
SHOULD BE FIRMLY ENTRENCHED WITHIN THE NEXT FEW HOURS. WITH THAT... 
IT WILL BE A MATTER OF COMPETING EFFECTS OF HORIZONTAL THERMAL 
ADVECTION /CAA IN SURFACE LAYER AND WAA ALOFT/ WITH LATENT HEAT 
EFFECTS. IN A NUTSHELL...SNOW FALLING INTO AN ABOVE-FREEZING LAYER 
WILL COOL THE LAYER FROM LATENT HEAT OF MELTING...AND RAIN FALLING 
INTO A SUB-FREEZING SURFACE LAYER WILL WARM THE LAYER FROM LATENT 
HEAT OF FREEZING. SHOULD BE ENOUGH ADVECTION TO COMPENSATE FOR THIS 
AND AT TIMES EVEN SURPASS THE DIABATIC EFFECTS.

NO SURPRISE ON OVERALL SYNOPTIC FIELDS. SURFACE CAD...SOUTHWEST FLOW 
ALOFT INITIALLY AS SHORTWAVE PUSHES EAST ACROSS THE SOUTHERN TIER OF 
THE COUNTRY AND CUTS OFF TOWARD THE END OF THE SHORT TERM. SURFACE 
LOW DEVELOPING IN THE NORTHERN GULF WILL CROSS EXTREME SOUTHEAST 
GEORGIA BEFORE PUSHING UP THE ATLANTIC COAST AND CAUSING MORE 
PROBLEMS UP THAT WAY. ECMWF AND GFS IN PRETTY GOOD AGREEMENT BUT 
ECMWF REMAINS ON THE WEST SIDE. VERY IMPRESSIVE SYNOPTIC LIFT 
ESPECIALLY TOWARD THE END OF THE PERIOD AS WE ARE SOLIDLY IN THE 
RIGHT ENTRANCE REGION OF THE UPPER JET.

THINK THERE IS STILL SOME CONVECTIVE FEEDBACK IN QPF FIELDS ON 
NAM/GFS BUT OVERALL SOLUTION IS PRETTY SIMILAR TO WHAT WE HAVE SEEN 
THE PAST FEW RUNS WITH AROUND 2 INCHES QPF ACROSS CENTRAL GEORGIA 
WITH AROUND AN INCH LIQUID ALONG THE NORTHERN TIER. AS THE WEATHER 
ENTERPRISE HAS BEEN ADVERTISING FOR DAYS NOW...WE ARE LOOKING AT 
MAINLY SNOW EXTREME NORTH...SNOW/SLEET/FZRA MIX ACROSS MOST OF THE 
METRO AREA...WITH MAINLY FZRA ON THE SOUTH SIDE. AS MENTIONED 
ABOVE...THIS IS A STORM OF HISTORICAL PROPORTIONS WITH POTENTIALLY 
CATASTROPHIC...CRIPPLING IMPACTS.

SNOW RATIOS UP NORTH RUN BETWEEN 6:1 AND 10:1 WHICH LINES UP WITH 
WITH OUR CLIMATOLOGICAL 8:1. OVERALL A WET SNOW /VERY GOOD FOR 
SNOWBALLS FOR THE KIDS HOME FOR SCHOOL...AND OF COURSE SOME PARENTS 
HOME FROM WORK/. IN ADDITION TO WHAT HAS ALREADY FALLING...EXPECTING 
A WIDESPREAD AREA OF GREATER THAN 4 INCHES OF SNOW AND SOME SLEET 
FROM GENERALLY ATLANTA TO ATHENS AND POINTS NORTH. A LARGE SWATH OF 
GREATER THAN 6 INCHES EXPECTED ACROSS THE EXTREME NORTHERN TIER. 
CANNOT RULE OUT SOME TOTALS UPWARDS OF A FOOT IN EXTREME NORTHEAST 
ZONES.

AS SIGNIFICANT AS THE SNOWFALL IS...AND MAKE NO MISTAKE THESE ARE 
SOME IMPRESSIVE TOTALS...IT IS THE ICE THAT WILL HAVE THE 
CATASTROPHIC IMPACTS. A LITTLE DIFFICULT TO DETERMINE THE NORTHERN 
EDGE OF THE ICE. FOR EXAMPLE AT AHN...THE GFS WARM NOSE IS A LITTLE 
COOLER THAN THE NAM AND WOULD RESULT IN MORE SLEET THAN FREEZING 
RAIN. HOWEVER...BECAUSE OF THE DEPTH OF THE WARM NOSE...AM STILL 
LEANING TOWARD KEEPING QUITE A BIT OF FZRA IN THAT AREA. SO WITH 
THAT...ICE TOTALS REMAIN VERY SIMILAR TO WHAT WAS PREVIOUSLY OUT BUT 
THINK THE 1/4 INCH LINE MAY BE A LITTLE FURTHER SOUTH AND MAX TOTALS 
ALONG THE EAST I-20 CORRIDOR ARE BUMPED UP A LITTLE TO OVER AN INCH. 
ISOLATED HIGHER AMOUNTS CANNOT BE RULED OUT. IN CASE IT HASNT BEEN 
MADE CLEAR ALREADY...THESE ARE CATASTROPHIC AND CRIPPLING TOTALS 
WHICH COULD RESULT IN WIDESPREAD POWER OUTAGES THAT MAY LAST FOR 
DAYS. IF RESIDENTS HAVE NOT COMPLETED THEIR PREPARATIONS IT MAY BE 
TOO LATE.

NORTHEAST WINDS WILL BE PRETTY BREEZY...GENERALLY 15-20MPH WITH 
GUSTS TO 25 OR POSSIBLY 30. ADD THESE WINDS TO THE AMOUNT OF ICE 
EXPECTED AND THAT WILL JUST EXACERBATE THE POWER LOSS ISSUES.

ALONG OUR SOUTHERN TIER OF COUNTIES WE EXPECT MAINLY RAIN BUT CANNOT 
RULE OUT SOME LIGHT FZRA RESULTING IN A GLAZE...SO WILL LEAVE THE 
FREEZING RAIN ADVISORY IN PLACE. WILL START THE ADVISORY A LITTLE 
EARLIER JUST TO COVER THE POTENTIAL FOR A LIGHT GLAZE THIS MORNING.

AS IF ALL THAT WASNT ENOUGH...STRENGTH OF FRONTOGENETICAL FORCING 
ALONG THE WEDGE FRONT PRETTY IMPRESSIVE...AND WITH THAT THERE IS 
SOME NEGATIVE SATURATED EQUIVALENT POTENTIAL VORTICITY ON TOP OF IT. 
THOSE ARE BIG GEEKY WORDS BUT BASICALLY IT MEANS THERE COULD BE SOME 
EMBEDDED /SYMMETRIC/ INSTABILITY TO DEAL WITH AND SO CANNOT RULE OUT 
SOME EMBEDDED CLAPS OF THUNDER. NOT ENOUGH OF A CONCERN TO ADD TO 
THE GRIDS BUT IF ANY CONVECTION DEVELOPS THAT COULD EASILY AND 
QUICKLY CHANGE THE P-TYPE. TRYING TO CATCH HOURLY P-TYPE IS NEARLY 
IMPOSSIBLE IN AN EVENT LIKE THIS SO IT IS BEST TO JUST FOCUS ON 
PREDOMINANT P-TYPE. 

AS THE UPPER LOW MOVES ACROSS...LAPSE RATES INCREASE AND 
TEMPERATURES DECREASE ENOUGH TO CHANGE P-TYPE TO ALL SNOW WITH SOME 
LIGHT ACCUMULATIONS POSSIBLE ON THE BACK SIDE. LUCKILY ON THURSDAY 
THE TEMPS SHOULD REBOUND INTO THE 40S ALL BUT EXTREME NORTHEAST 
MOUNTAINS. I WANT TO ADD A CAVEAT THAT GUIDANCE IS HORRIBLE AT 
TEMPERATURES WITH SNOWPACK...SO WHERE THE SNOW COVER IS TONIGHT IT 
IS ENTIRELY POSSIBLE THAT LOW TEMPS MIGHT BE SIGNIFICANTLY LOWER 
THAN CURRENT FORECASTS ARE ADVERTISING /LIKE WHAT HAPPENED A COUPLE 
OF WEEKS AGO/...AND HIGHS ON THURSDAY MAY BE KEPT LOWER. WILL 
REEVALUATE THIS WITH LATER FORECASTS.

PRETTY SURE THAT THERE ARE SOME THINGS I HAVENT COVERED HERE BUT 
HOPEFULLY THIS LIGHT READING MATERIAL IS GOOD ENOUGH TO GET 
EVERYONES DAY STARTED. THE BOTTOM LINE...AS THE ENTIRE WEATHER 
ENTERPRISE HAS BEEN ADVERTISING FOR DAYS NOW... 
THIS-IS-AN-EVENT-OF-HISTORICAL-PROPORTIONS!! 
CATASTROPHIC...CRIPPLING...PARALYZING...CHOOSE YOUR ADJECTIVE. THIS 
IS A VERY VERY BIG DEAL ESPECIALLY FROM METRO ATLANTA EAST ALONG THE 
I-20 CORRIDOR...GENERALLY ANYWHERE SOUTH OF I-85 AND NORTH OF I-16 
WHERE THE MOST SIGNIFICANT ICE TOTALS ARE FORECAST. STAY SAFE OUT 
THERE!

TDP

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
/ISSUED AT 339 AM EST WED FEB 12 2014/
NEXT CONCERN WILL BE A FAST MOVING COLD FRONT AND ASSOCIATED UPPER 
TROUGH FORECAST TO MOVE ACROSS THE AREA FRIDAY AFTERNOON AND NIGHT. 
ASSOCIATE MOISTURE BRINGS PRECIP CHANCES MAINLY INTO N GA FRIDAY 
AFTERNOON AND ACROSS THE AREA FRIDAY NIGHT. TEMPERATURES APPEAR COLD 
ENOUGH FOR A RAIN SNOW MIX OR A CHANGE OVER TO SNOW FRIDAY EVENING 
FOR PORTIONS OF N GA WITH A DUSTING POSSIBLE FOR FAR N FULTON COUNTY 
AND NE TO THE MOUNTAINS.

MODELS RATHER INCONSISTENT BRINGING MOISTURE ACROSS N GA SATURDAY 
NIGHT ASSOCIATED WITH A WEAK UPPER TROUGH. TEMPERATURES COLD ENOUGH 
FOR LIGHT RAIN OR SNOW WITH NO SIGNIFICANT ACCUMULATIONS EXPECTED AT 
THIS TIME. 

GFS AND EUROPEAN DIFFERING WITH A COLD FRONT EARLY NEXT WEEK. GFS 
MUCH FASTER BRINGIMG A COLD FRONT ACROSS THE AREA MONDAY NIGHT AND 
TUESDAY AND THE EUROPEAN BRINGING THE FRONT ACROSS THE AREA TUESDAY 
AFTERNOON AND NIGHT. AT THIS TIME FAVORING THE WPC POP GRID FOR 
MONDAY NIGHT WITH CHANCE POPS ACROSS NORTH AND PORTIONS OF CENTRAL 
GA. THIS COULD CHANGE GREATLY WITH OTHER MODEL RUNS. AT THIS TIME 
AIRMASS SEEMS TO SUPPORT LIGHT RAIN OR LIGHT SHOWERS ONLY.

BDL

&&

.AVIATION...
12Z UPDATE...
FZRA WAS FALLING IN ATL AREA ALONG WITH AHN. CSG AND MCN SHOULD 
SWITCH OVER TO FZRA BY 13/14Z...HOWEVER CSG WILL SWITCH BACK TO RAIN 
AS THE SURFACE LOW EDGES A LITTLE CLOSER BRINGING IN SOME WARMER 
AIR. THE FZRA WILL CONTINUE INTO THIS EVENING...THEN SWITCH OVER TO 
SNOW BEFORE ENDING AFTER MIDNIGHT TONIGHT. WINDS WILL REMAIN 
EAST/NORTHEAST UP TO 30KTS THIS MORNING WITH SOME DIMINISHING THIS 
AFTERNOON. WINDS WILL SWITCH TO THE NORTHWEST AFTER MIDNIGHT AS THE 
SURFACE LOW PULLS OFF TO OUR SOUTHEAST. IFR/MVFR CLOUDS WILL BECOME 
ALL IFR AND REMAIN IFR INTO TONIGHT.

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

17

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          29  28  40  31 / 100 100  40   0 
ATLANTA         31  27  41  34 / 100 100  20   0 
BLAIRSVILLE     32  29  39  25 / 100 100  40   5 
CARTERSVILLE    32  29  42  30 / 100 100  20   0 
COLUMBUS        36  30  48  36 / 100 100  10   0 
GAINESVILLE     29  27  41  32 / 100 100  40   0 
MACON           33  29  45  32 / 100 100  20   0 
ROME            34  29  43  29 / 100 100  20   5 
PEACHTREE CITY  32  27  43  30 / 100 100  20   0 
VIDALIA         34  31  48  35 / 100 100  20   0 

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
ICE STORM WARNING UNTIL 1 PM EST THURSDAY FOR THE FOLLOWING 
ZONES: BALDWIN...BIBB...BLECKLEY...BUTTS...CARROLL...CLARKE...
CLAYTON...COWETA...CRAWFORD...DOUGLAS...EMANUEL...FAYETTE...
GLASCOCK...GREENE...HANCOCK...HEARD...HENRY...HOUSTON...JASPER...
JEFFERSON...JOHNSON...JONES...LAMAR...LAURENS...MADISON...
MERIWETHER...MONROE...MORGAN...NEWTON...OCONEE...OGLETHORPE...
PEACH...PIKE...PUTNAM...ROCKDALE...SOUTH FULTON...SPALDING...
TALIAFERRO...TREUTLEN...TROUP...TWIGGS...UPSON...WALTON...
WARREN...WASHINGTON...WILKES...WILKINSON.

FREEZING RAIN ADVISORY UNTIL 1 PM EST THURSDAY FOR THE FOLLOWING 
ZONES: CHATTAHOOCHEE...CRISP...DODGE...DOOLY...HARRIS...MACON...
MARION...MONTGOMERY...MUSCOGEE...PULASKI...SCHLEY...STEWART...
SUMTER...TALBOT...TAYLOR...TELFAIR...TOOMBS...WEBSTER...
WHEELER...WILCOX.

WINTER STORM WARNING UNTIL 1 PM EST THURSDAY FOR THE FOLLOWING 
ZONES: BANKS...BARROW...BARTOW...CATOOSA...CHATTOOGA...
CHEROKEE...COBB...DADE...DAWSON...DEKALB...FANNIN...FLOYD...
FORSYTH...GILMER...GORDON...GWINNETT...HALL...HARALSON...
JACKSON...LUMPKIN...MURRAY...NORTH FULTON...PAULDING...PICKENS...
POLK...TOWNS...UNION...WALKER...WHITE...WHITFIELD.

&&

$$

SHORT TERM...TDP
LONG TERM....BDL
AVIATION...17

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