National Weather Service Raw Text Product

830 
FXUS62 KFFC 181137 AAA
AFDFFC

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
637 AM EST MON FEB 18 2013

.PREV DISCUSSION... /ISSUED 359 AM EST MON FEB 18 2013/ 

SHORT TERM /TODAY THROUGH TUESDAY/...
VERY QUIET DAY EXPECTED FOR TODAY...WITH WEAK RIDGING ALOFT AND 
SURFACE HIGH PRESSURE MOVING EAST OFF THE CAROLINAS INTO THE WESTERN 
ATLANTIC. TROUGH PUSHING OFF THE ROCKIES AND ATTENDANT SURFACE LOW 
IN THE CENTRAL PLAINS WILL BE THE MAIN WEATHER MAKER FOR THE SHORT 
TERM...BRINGING A QUICK SHOT OF SHOWERS TO THE AREA ON TUESDAY. AS 
THE TROUGH DEEPENS IN THE PLAINS TODAY...THE WAVETRAIN AMPLITUDE 
WILL INCREASE...INCREASING THE DIFFLUENCE ALOFT AND STRENGTHENING 
THE SURFACE FRONT AS IT APPROACHES. HOWEVER...BY 12Z TUESDAY THE 
FRONT WILL BEGIN TO OCCLUDE WITH BEST DYNAMICS REMAINING WELL TO THE 
NORTH ASSOCIATED WITH THE SURFACE AND UPPER LOWS...SO THE FRONT WILL 
BEGIN TO WEAKEN AS IT MOVES THROUGH. OVERALL THERE IS GENERAL 
AGREEMENT BETWEEN THE MODELS FOR THE SHORT-TERM ESPECIALLY WITH MASS 
FIELDS. IF A PREFERENCE HAD TO BE DEFINED...IT WOULD BE WEAKLY GFS 
BASED ON MORE CONSISTENT TRENDS BUT FOR MOST PART STARTED WITH A 
GENERIC BLEND FOR ELEMENTS THROUGHOUT THE SHORT TERM.

HAVE POPS MOVING INTO NORTHWEST GEORGIA BY AROUND 06Z TUESDAY...WITH 
LIKELY TO CATEGORICAL SPREADING ACROSS NORTH GEORGIA THROUGH 12Z BUT 
DIMINISHING INTO CENTRAL GEORGIA BY 18Z. POPS PRETTY MUCH CLEAR OUT 
BY 00Z WEDNESDAY. OVERALL QPF VALUES NOT PARTICULARLY IMPRESSIVE 
WITH STORM TOTAL /AT LEAST FOR THIS EVENT/ OF BETWEEN 0.25 TO 0.5 
INCHES. MAIN WEATHER TYPE WILL BE SHOWERS...BUT CONCERN IS THE 
POSSIBILITY OF THUNDER SOUTH AND WINTRY PRECIP IN THE MOUNTAINS.

FOR THE THUNDER...SPC DOES HAVE JUST A SLIVER OF WEST CENTRAL 
GEORGIA IN GENERAL THUNDER FOR DAY1...AND EXTREME SOUTHERN PORTIONS 
OF THE AREA IN GENERAL THUNDER FOR DAY2...BUT LOOKING AT MUCAPE 
VALUES JUST DO NOT SEE ENOUGH TO SUPPORT THUNDER AT THIS TIME. DAY 
SHIFT CAN REEVALUATE BASED ON 12Z GUIDANCE BUT FOR NOW HAVE 
CONTINUED TREND OF LEAVING IT OUT. 

FOR WINTRY PRECIP IN THE MOUNTAINS...00Z GUIDANCE IS COMING IN 
COLDER AND MORE MOIST THAN PREVIOUS RUNS. GFS IS THE COLDEST AND NAM 
THE WARMEST...WITH NEW 00Z ECMWF BETWEEN THE TWO BUT SLIGHTLY CLOSER 
TO THE NAM. THERE WILL BE A CRITICAL WINDOW AHEAD OF THE FRONT WHEN 
PRECIP MOVES IN BUT TEMPERATURES WILL BE COLD ENOUGH TO SUPPORT SOME 
FREEZING OR FROZEN PRECIPITATION IN THE MOUNTAINS. OVERALL LOW 
TEMPS WILL DEPEND ON EXTENT OF CLOUD COVER AHEAD OF THE SYSTEM BUT 
THINK THAT WE SHOULD GET SOME RADIATIONAL COOLING BEFORE THE PRECIP 
MOVES IN. HAVE LOW TEMPS IN THE MOUNTAINS AT OR JUST SLIGHTLY BELOW 
FREEZING. THE DIFFICULTY LIES IN THE SOUNDING DETAILS...ESPECIALLY 
CONSIDERING THE WAA AHEAD OF THE SYSTEM AT 850MB...LEADING TO A WARM 
NOSE. GFS BUFR SOUNDINGS FOR BRASSTOWN BALD INDICATE ALL SNOW /WARM 
NOSE DOES NOT GET ABOVE FREEZING/...BUT NAM BUFR SOUNDINGS INDICATE 
ALL LIQUID REACHING THE SURFACE LAYER DUE TO THE STRENGTH OF THE 
WARM NOSE...WITH FINAL P-TYPE DEPENDENT ON SURFACE TEMPS. CONFIDENCE 
NOT PARTICULARLY HIGH GIVEN THESE DIFFERENCES BUT FEEL IT IS LIKELY 
THAT AT LEAST SOME SORT OF WINTRY PRECIP WILL MAKE IT TO THE 
GROUND...SO TOOK A BLEND OF BOTH...STUCK THE TEMPS AND POPS IN THE 
BLENDER WITH THE TOP-DOWN METHODOLOGY...AND RESULTANT WEATHER GRIDS 
GIVE MAINLY A RAIN/SLEET MIX ACROSS THE MOUNTAINS WITH A LITTLE SNOW 
EARLY ON BEFORE THE 850MB TEMPS BEGIN WARMING...AND PERHAPS SOME 
FREEZING RAIN MIXED IN HERE AND THERE. SINCE THE PERIOD OF TIME WITH 
AT OR BELOW FREEZING TEMPS IS ONLY FOR A COUPLE OF HOURS AT BEST 
AROUND 12Z TUESDAY...AND THEN TEMPS BEGIN TO WARM AGAIN...EXPECT 
VERY LITTLE IF ANY ACCUMULATION OF WHATEVER ENDS UP OCCURRING. IF 
ANYTHING DOES BEGIN TO ACCUMULATE...IT SHOULD MELT QUICKLY WITH THE 
WARMING TEMPS AND CHANGEOVER TO LIQUID PRECIP AFTER 12Z. SO...LONG 
STORY SHORT...EXPECT A BRIEF SHOT OF JUST ABOUT EVERY P-TYPE OUT 
THERE ACROSS THE NORTHEAST MOUNTAINS...PRIMARILY BETWEEN 09-13Z BUT 
NO ACCUMULATIONS. NO WINTER WEATHER PRODUCTS PLANNED AT THIS TIME... 
BUT WILL MENTION THE POSSIBILITY IN THE HWO.

OTHER CONCERN IS STRONG WINDS AHEAD OF THE FRONT WITH 925-850MB LLJ 
OF 40-50KT MOVING IN ACROSS NORTH GEORGIA...BUT FOR RIGHT NOW WINDS 
REMAIN JUST BELOW ADVISORY CRITERIA.

OBVIOUSLY THIS LEAVES A LOT FOR LATER SHIFTS TO REEVALUATE WITH 12Z 
GUIDANCE.

TDP

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
LONG RANGE ECMWF AND GFS MODELS CONTINUE TO SHOW GOOD AGREEMENT...
AT LEAST INITIALLY THROUGH FRIDAY... WITH HIGH PRESSURE DOMINATING
TUESDAY NIGHT THROUGH EARLY THURSDAY... THEN WEAKENING ITS GRIP IN
RESPONSE TO A LOW PRESSURE SYSTEM AND ASSOCIATED COLD FRONT PUSHING
EAST OF THE PLAINS ON THURSDAY. MODELS AGREE WITH SHOWERS AND
POSSIBLY A FEW EMBEDDED THUNDERSTORMS SPREADING INTO NORTH GEORGIA
THURSDAY NIGHT... THEN INTO CENTRAL GEORGIA ON FRIDAY ALONG AND
AHEAD OF A COLD FRONT. BOTH MODELS SHOW 200-400 CAPE NOSING INTO
PARTS OF CENTRAL GEORGIA ON FRIDAY DURING DAYTIME HEATING. THIS
LOCATION AND TIMING WILL LIKELY BE THE GREATER CHANCE FOR THUNDER.
THE NOTED MARGINAL INSTABILITIES AND UPPER SUPPORT DOES SUGGEST ANY
STORM DEVELOPMENT WILL LIKELY REMAIN UNDER SEVERE LIMITS. HOWEVER...
THIS COULD CHANGE AND ALL INTERESTS ARE ENCOURAGED TO MONITOR
CLOSELY LATER FORECASTS. AS FOR THE WEEKEND... THE MODELS DIVERGE...
WITH THE FASTER GFS PUSHING THE COLD FRONT EAST BY SATURDAY MORNING
WITH DRY HIGH PRESSURE DOMINATING SATURDAY AND SUNDAY. THE SLOWER/WETTER
ECMWF STALLS THE FRONT ACROSS CENTRAL GEORGIA ON SATURDAY AND HOLDS
OFF CLEARING IT AND THE ASSOCIATED SHOWERS EAST UNTIL SUNDAY
MORNING. TOOK A BLEND WITH A SLIGHT LEAN TOWARD THE DRIER/CLEANER
GFS... AND HELD ONTO A SLIGHT CHANCE OF RAIN ACROSS PARTS OF
CENTRAL GEORGIA FOR SATURDAY AND SUNDAY. 39

FIRE WEATHER...
FUEL MOISTURES DROPPED TO NEAR 8 PERCENT YESTERDAY ACROSS A LARGE 
PORTION OF THE AREA...HOWEVER NEW GUIDANCE COMING IN IS SPEEDING UP 
THE MOISTURE RETURN TODAY LEAVING JUST MARGINAL FIRE DANGER 
CONDITIONS. SINCE FIRE DANGER STATEMENT IS ALREADY OUT HAVE REISSUED 
AND ADJUSTED WORDING. ANY FIRE WEATHER ISSUES AFTER TODAY WILL BE 
DEPENDENT ON FUEL MOISTURES. 

TDP

&&

.AVIATION...
12Z UPDATE...
VFR THROUGH ABOUT 10Z TUESDAY MORNING...THOUGH LOW VFR CLOUDS
SHOULD START TO INCREASE BETWEEN 06-08Z /LATER SOUTH AND EAST/.
-SHRA MOVES IN BETWEEN 08-10Z WITH MVFR CIGS BY 10Z AS WELL.
SHOULD SEE AT LEAST A BRIEF PERIOD OF IFR CONDITIONS...CURRENT
TIMING FOR THE METRO AREA IS 13-16Z BUT WILL HAVE TO BE REFINED.
IMPROVEMENT BACK TO MVFR BEFORE THE END OF THE ATL PERIOD. LIGHT
SSE WINDS THIS MORNING INCREASE TO AROUND 10KT THIS AFTERNOON...
SHIFTING TO SSW 12-13Z TUESDAY.

//ATL CONFIDENCE...12Z UPDATE...
MEDIUM ON TIMING OF ELEMENTS /LOWERING CIGS...WIND SHIFTS/
MEDIUM ON CIG HEIGHTS TUESDAY MORNING
HIGH ON WIND SPEEDS...WX...AND VSBY

TDP

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          58  38  57  28 /   0  60  80   5 
ATLANTA         57  41  55  30 /   0  70  80   5 
BLAIRSVILLE     52  32  49  22 /   0  80  80   5 
CARTERSVILLE    58  39  55  27 /   0  80  80   5 
COLUMBUS        61  45  62  32 /   0  50  80   5 
GAINESVILLE     54  37  52  29 /   0  70  80   5 
MACON           60  41  62  30 /   0  40  80  10 
ROME            59  39  55  26 /   0  80  80   5 
PEACHTREE CITY  59  39  58  26 /   0  70  80   5 
VIDALIA         60  43  66  36 /   0  30  50  20 

&&

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

$$