Special Weather Statement, NWS Atlanta, GA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
748 PM EST TUE DEC 23 2014

.UPDATE...
LINE OF STRONG TO SEVERE THUNDERSTORMS ACROSS CENTRAL AL CONTINUES
EASTWARD THIS EVENING. THE LINE IS HOLDING STEADY AND IS EXPECTED
TO REACH THE AL/GA STATE LINE AROUND 10 PM. THE HRRR BEGINS TO
WEAKEN THE LINE RIGHT ALONG THE INTERSTATE 85 CORRIDOR RIGHT
AROUND OR JUST AFTER MIDNIGHT. GRADUAL WEAKENING OF THE LINE WOULD
OCCUR IF THE WEDGE CONTINUED TO HOLD STRONG EAST OF 85.
HOWEVER...STORMS SHOULD BECOME ELEVATED ACROSS THE EASTERN
PORTIONS OF THE CWFA. DO THINK SOME CONTINUED EROSION ON THE WEST
SIDE OF THE WEDGE IS LIKELY...BUT NOT CONFIDENCE ON EXACTLY HOW
MUCH.

HAVE MADE SOME TIMING TWEAKS FOR TSRA WITHIN THE GRIDS. IN
ADDITION...TWEAKED THE HOURLY TEMP/DEW GRIDS ACCORDING TO THE
POSITION OF THE WARM FRONT.

&&

.PREV DISCUSSION... /ISSUED 622 PM EST TUE DEC 23 2014/

PREV DISCUSSION... /ISSUED 244 PM EST TUE DEC 23 2014/

.SEVERE STORMS REMAIN POSSIBLE TONIGHT AND WEDNESDAY...
.HEAVY RAINFALL AND MINOR FLOODING LIKELY TONIGHT AND
WEDNESDAY...

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
OVERALL FCST IN GOOD SHAPE. WARM FRONT STILL VERY SLOW TO MOVE
NORTH BUT SHOULD MARCH SLOWLY NORTH TONIGHT.

MONITORING SEVERE STORM IN NW GA THAT HAS HISTORY OF PRODUCING
DAMAGING WINDS. STORM MAY HAVE TRAVELED ALONG WRN PERIPHERY OF
WEDGE. WILL BE A FEW HOURS BEFORE NORTH GA SEES ANOTHER ROUND OF
POSSIBLE SVR STORMS. AS MENTIONED IN PREV DISCUSSION /SEE UPDATE
SECTION BELOW/ INGREDIENTS REMAIN IN PLACE FOR SVR STORMS TONIGHT
AND WED MORNING...GREATEST THREAT 03Z-15Z OR SO.

AS FRONT SWEEPS THRU WED AFTERNOON...SHOULD SEE RAPID END TO PRECIP
AND ERODING OF LOW CLOUDS. NOT MUCH CHC FOR WINTER PRECIP WED NIGHT
EVEN IN HIGHER ELEVATIONS. SOME IN ELEV ABOVE 2500FT MAY SEE A BRIEF
MIX OF LIGHT RAIN WITH SNOW FLURRIES BUT NO IMPACTS EXPECTED.

SNELSON

UPDATE...
/ISSUED AT 129 PM EST TUE DEC 23 2014/
FCST GRIDS UPDATED EARLIER THIS MORNING TO ACCOUNT FOR OBSERVED
TRENDS. 12Z MODELS...PARTICULARLY GFS...TOO QUICK LIFTING WARM
FRONT WHICH IS CURRENTLY LOCATED FROM AROUND COLUMBUS TO VIDALIA.
TEMPS WILL LIKELY REMAIN IN THE 40S IN NORTH GA AND 50S TO 60S
OVER MIDDLE GA.

COVERAGE OF RAINFALL OVER AL A LITTLE LESS THAN WHAT 12Z HIRES
MODELS INDICATING...POSSIBLY DUE TO LARGE EXPANDING AREA OF
CONVECTION OVER SRN AL AND SW GA. NEW 18Z CYCLE WPC QPF GUIDANCE
INDICATING ABOUT 1-2 INCHES OVER AREAS NORTH OF COLUMBUS TO MACON.
WILL REVIEW THIS BEFORE RELEASING FINAL FORECAST. BASED ON PREV
FCST AND ALREADY SOME REPORTS OF NUISANCE/MINOR FLOODING HAVE
ISSUED FLOOD WATCH FOR ALL OF CWA.

THREAT FOR SEVERE WX STILL IN PLACE THOUGH CONCERNED ABOUT
POSSIBLE UPSTREAM CONVECTION MENTIONED EARLIER DISRUPTING VERTICAL
WIND SHEAR AND INSTABILITY. THAT SAID...STILL SEEING FAIRLY STRONG
ISOLATED CELLS IN NRN/WRN AL ATTM WHERE MLCAPE VALUES TRYING TO
CREEP UP TO 250-500 J/KG. 0-1KM BULK SHEAR ONLY 20-30KTS IN AL.
12Z MODEL VALUES FOR TONIGHT SILL FAVORABLE FOR HIGH SHEAR LOW
CAPE CONVECTION AND QLCS MODES. NAM STILL HIGHER THAN GFS FOR
SHEAR AND MLCAPE...AVERAGING AROUND 100-300 J/KG MLCAPE AND 35-45
FOR 0-1KM BULK SHEAR. SHEAR DROPS SOME DURING DAY ON WED SO
TORNADO THREAT MAY LOWER ACCORDINGLY.

CONTINUING TO MONITOR.

SNELSON

LONG TERM /THURSDAY THROUGH TUESDAY/...
BEHIND A COLD FRONT THAT PUSHES EAST OF THE AREA EARLY THURSDAY
MORNING... WRAP AROUND CLOUDS AND MOISTURE MAY BE A BIT SLOW TO
CLEAR FROM WEST TO EAST THURSDAY MORNING DUE TO A LAGGING STRONG
UPPER DISTURBANCE THAT DOES NOT PUSH EAST OF THE STATE UNTIL EARLY
THURSDAY AFTERNOON. OTHERWISE... EXPECT DRY HIGH PRESSURE TO BUILD
OVER THE AREA THURSDAY AFTERNOON WITH CLEARING CONDITIONS AND HIGH
TEMPERATURES MOSTLY IN THE 50S. THE COOLEST TEMPERATURES WILL BE
FELT FRIDAY MORNING WITH LOWS MOSTLY IN THE 30S. THEN MODELS AGREE
ON THE SURFACE RIDGE SHIFTING EAST ON FRIDAY...AND ESTABLISHING A
WARMING...MOIST SOUTHERLY FLOW GOING INTO THE WEEKEND. THIS AHEAD OF
ANOTHER LOW PRESSURE SYSTEM THAT SHOULD BRING RAIN CHANCES TO THE
AREA OVER THE WEEKEND. LONG RANGE MODELS STILL SHOW SOME TIMING
DIFFERENCES... WITH THE FASTER GFS SPREADING SHOWERS INTO THE AREA
ON SATURDAY...AND HOLDING RAIN CHANCES ACROSS THE AREA INTO MONDAY
WHEN A SLOW MOVING COLD FRONT FINALLY TRAVERSES THE AREA. THE SLOWER
ECMWF HOLD RAIN CHANCES OFF UNTIL MAINLY SUNDAY...BUT THEN DOES SHOW
A COLD FRONT PUSHING ACROSS THE AREA MONDAY NIGHT-EARLY TUESDAY...
WITH BOTH SHOWING HIGH PRESSURE AND DRIER CONDITIONS IN CONTROL BY
TUESDAY. AT THIS TIME... LACK OF INSTABILITY AND STRONG UPPER
FORCING WARRANTS ONLY SHOWERS SO FAR WITH THIS SYSTEM... HOWEVER
THIS COULD CHANGE SO STAY TUNED.

39

HYDROLOGY...
DECIDED TO PLAY IT SAFE AND POST A FLOOD WATCH FOR MOST OF NORTH
AND CENTRAL GA THROUGH 8 PM WEDNESDAY DUE TO THE EXPECTED 2 TO 3
INCHES OF ADDITIONAL RAINFALL THROUGH WEDNESDAY AFTERNOON AHEAD OF
A COLD FRONT. ISOLATED HIGHER AMOUNTS ARE ALMOST CERTAIN... AND
WITH NEARLY 100 PERCENT RUNOFF OF ANY RAINFALL INTO CREEKS...
STREAMS AND RIVERS THIS TIME OF YEAR... RAPID RISES ARE
EXPECTED...THAT COULD RESULT IN FLOODING. IN ADDITION TO RIVER
FLOODING... ISOLATED FLASH FLOODING IS ALSO POSSIBLE DUE TO FALL
VEGETATION AND OTHER DEBRIS CLOGGING DRAINAGE SYSTEMS OR NARROWS
ALONG CREEKS AND STREAMS. ALL INTEREST ACROSS NORTH AND CENTRAL GA
SHOULD MONITOR CONDITIONS CLOSELY AND BE ALERT FOR POSSIBLE FLOOD
WARNINGS. THOSE LIVING IN AREAS PRONE TO FLOODING SHOULD BE
PREPARED TO TAKE ACTION SHOULD FLOODING DEVELOP. THE RAINFALL
SHOULD END FROM WEST TO EAST WEDNESDAY AFTERNOON AND GREATLY
LESSON THE THREAT OF FLOODING BY WEDNESDAY EVENING.

AVIATION...
00Z UPDATE...
WARM FRONT WILL CONTINUE TO MOVE NORTH ACROSS CENTRAL GA THIS
EVENING. A LINE OF THUNDERSTORMS AHEAD OF A COLD FRONT SHOULD
IMPACT ATL BETWEEN 04Z AND 07Z ACCORDING TO THE LATEST TIMING OF
THE HRRR. THE CIG FORECAST MAY BE TRICKY...IF THE WARM FRONT MOVES
NORTH OF ATL...CIGS COULD BRIEFLY IMPROVE. HOWEVER...BELIEVE WITH
THE STRONG WEDGE IN PLACE...GOING TO LEAVE THEM AT LIFR. SLOW
IMPROVEMENT TOMORROW TO MVFR. WINDS SHOULD BEGIN TO SHIFT TO THE
SW BY THE AFTERNOON.

//ATL CONFIDENCE...00Z UPDATE...
HIGH CONFIDENCE ON TIMING OF LINE OF THUNDER. LOW-MED CONFIDENCE
ON CIGS.

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          46  45  66  40 / 100 100 100  30
ATLANTA         50  48  65  39 / 100 100 100  10
BLAIRSVILLE     55  43  58  35 / 100 100 100  30
CARTERSVILLE    50  49  64  37 / 100 100  90  10
COLUMBUS        64  62  66  40 / 100 100  90  10
GAINESVILLE     44  42  61  39 / 100 100 100  30
MACON           56  55  68  41 / 100 100 100  20
ROME            52  50  62  37 / 100 100  90  10
PEACHTREE CITY  54  53  66  37 / 100 100 100  10
VIDALIA         58  56  71  47 / 100 100 100  30

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH THROUGH WEDNESDAY EVENING FOR THE FOLLOWING ZONES:
BALDWIN...BANKS...BARROW...BARTOW...BIBB...BLECKLEY...BUTTS...
CARROLL...CATOOSA...CHATTAHOOCHEE...CHATTOOGA...CHEROKEE...
CLARKE...CLAYTON...COBB...COWETA...CRAWFORD...CRISP...DADE...
DAWSON...DE KALB...DODGE...DOOLY...DOUGLAS...EMANUEL...FANNIN...
FAYETTE...FLOYD...FORSYTH...GILMER...GLASCOCK...GORDON...
GREENE...GWINNETT...HALL...HANCOCK...HARALSON...HARRIS...HEARD...
HENRY...HOUSTON...JACKSON...JASPER...JEFFERSON...JOHNSON...
JONES...LAMAR...LAURENS...LUMPKIN...MACON...MADISON...MARION...
MERIWETHER...MONROE...MONTGOMERY...MORGAN...MURRAY...MUSCOGEE...
NEWTON...NORTH FULTON...OCONEE...OGLETHORPE...PAULDING...PEACH...
PICKENS...PIKE...POLK...PULASKI...PUTNAM...ROCKDALE...SCHLEY...
SOUTH FULTON...SPALDING...STEWART...SUMTER...TALBOT...
TALIAFERRO...TAYLOR...TELFAIR...TOOMBS...TOWNS...TREUTLEN...
TROUP...TWIGGS...UNION...UPSON...WALKER...WALTON...WARREN...
WASHINGTON...WEBSTER...WHEELER...WHITE...WHITFIELD...WILCOX...
WILKES...WILKINSON.

TORNADO WATCH UNTIL MIDNIGHT EST TONIGHT FOR THE FOLLOWING
ZONES: CHATTAHOOCHEE...HARRIS...HEARD...MARION...MUSCOGEE...
SCHLEY...STEWART...SUMTER...TROUP...WEBSTER.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
415 PM EST TUE DEC 23 2014

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-241100-
BALDWIN-BANKS-BARROW-BARTOW-BIBB-BLECKLEY-BUTTS-CARROLL-CATOOSA-
CHATTAHOOCHEE-CHATTOOGA-CHEROKEE-CLARKE-CLAYTON-COBB-COWETA-
CRAWFORD-CRISP-DADE-DAWSON-DE KALB-DODGE-DOOLY-DOUGLAS-EMANUEL-
FANNIN-FAYETTE-FLOYD-FORSYTH-GILMER-GLASCOCK-GORDON-GREENE-
GWINNETT-HALL-HANCOCK-HARALSON-HARRIS-HEARD-HENRY-HOUSTON-JACKSON-
JASPER-JEFFERSON-JOHNSON-JONES-LAMAR-LAURENS-LUMPKIN-MACON-
MADISON-MARION-MERIWETHER-MONROE-MONTGOMERY-MORGAN-MURRAY-
MUSCOGEE-NEWTON-NORTH FULTON-OCONEE-OGLETHORPE-PAULDING-PEACH-
PICKENS-PIKE-POLK-PULASKI-PUTNAM-ROCKDALE-SCHLEY-SOUTH FULTON-
SPALDING-STEWART-SUMTER-TALBOT-TALIAFERRO-TAYLOR-TELFAIR-TOOMBS-
TOWNS-TREUTLEN-TROUP-TWIGGS-UNION-UPSON-WALKER-WALTON-WARREN-
WASHINGTON-WEBSTER-WHEELER-WHITE-WHITFIELD-WILCOX-WILKES-
WILKINSON-
415 PM EST TUE DEC 23 2014

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH AND CENTRAL GEORGIA.

.DAY ONE...TONIGHT...TUESDAY NIGHT.

...SCATTERED THUNDERSTORMS ARE EXPECTED TONIGHT OVER MUCH OF NORTH AND
CENTRAL GEORGIA. A FEW THUNDERSTORMS MAY BECOME SEVERE OVER CENTRAL AND
PORTIONS OF NORTH GEORGIA...
...HEAVY RAIN COULD CAUSE MINOR FLOODING...

WEATHER HAZARDS EXPECTED...
DAMAGING WINDS...ISOLATED TORNADOES AND LARGE HAIL...WITH ANY STRONG TO
SEVERE THUNDERSTORM. HEAVY RAIN COULD CAUSE MINOR FLOODING.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY...

A STRONG COLD FRONT WILL MOVE THROUGH GEORGIA ON WEDNESDAY. SHOWERS
AND SCATTERED THUNDERSTORMS ARE EXPECTED AHEAD OF THE FRONT. SOME
OF THESE STORMS COULD BE SEVERE WITH DAMAGING WINDS...ISOLATED
TORNADOES...AND HEAVY RAIN. THE BEST RISK FOR SEVERE STORMS ON
WEDNESDAY WILL BE ALONG AND AHEAD OF THE COLD FRONT THAT WILL
MOVE INTO WESTERN GEORGIA WEDNESDAY MORNING...AND INTO EASTERN
GEORGIA BY WEDNESDAY AFTERNOON.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT REQUESTED BUT SPOTTERS ARE ENCOURAGED
TO SUBMIT REPORTS OF SEVERE WEATHER THROUGH THE WEB BY GOING TO
WEATHER.GOV/ATLANTA.

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