Area Forecast Discussion

000
FXUS62 KFFC 232139
AFDFFC

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
538 PM EDT THU OCT 23 2008

.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
DEEP VERTICALLY STACKED CLOSED LOW WILL CONTINUE TO ROTATE SLOWLY
FROM CENTRAL KS TOWARD N IL THROUGH FRI. A STRONG...NEGATIVELY
TILTED LEADING SHORT WAVE WILL MOVE RAPIDLY INTO THE SE U.S. FROM
THE MID-SOUTH TONIGHT AND FRIDAY...SWEEPING INTO SC BY 00Z SAT.
MEANWHILE...A CLASSIC WEDGE SETUP IN PLACE WITH A LARGE CANADIAN
HIGH PARKED OVER THE NE U.S. INTO THE MID-ATLANTIC WITH A HIGH
AMPLITUDE RIDGE ALIGNED ALONG THE EAST COAST. SFC AIR MASS INITIALLY
VERY DRY WITH DEWPOINTS IN THE 30S NORTH AND 40S SOUTH. MID-LEVEL
WARM ADVECTION ALREADY WELL UNDER WAY WITH EXPANDING FIELD OF
MID/HIGH CLOUDS OVER THE CWA. CEILINGS WILL CONTINUE TO LOWER AS THE
SHORT WAVE APPROACHES AND IMPRESSIVE ISENTROPIC LIFT WILL ENSUE.
WEAK ECHO RETURNS ALREADY EVIDENT ACROSS MS/W AL...AND THIS WILL
CONTINUE TO INCREASE AND SPREAD INTO GA BETWEEN 00Z-06Z. SIGNIFICANT
WETBULB COOLING WILL TAKE PLACE WHEN THE RAIN BEGINS...AND THIS WILL
SERVE TO INTENSIFY THE WEDGE ALREADY IN PLACE. FRI WILL CERTAINLY BE
A RAW...BREEZY...AND UNSEASONABLY COLD DAY...LIKELY THE COLDEST
DAYTIME TEMPERATURES WE HAVE SEEN SINCE FEBRUARY OR EARLY MARCH.

FOR RAINFALL AMOUNTS...SYSTEM WILL BE FAST MOVING...AND MID-LEVEL
MOISTURE ALREADY PULLING OUT OF THE CWA IN THE 18Z-00Z TIME FRAME.
EXPECT HEAVIEST RAIN TO IMPACT THE CWA FROM WEST TO EAST IN THE
06Z-18Z TIME FRAME. GFS QPF APPEARS TO BE MORE REASONABLE TODAY WITH
MINIMAL CONVECTIVE FEEDBACK. A DEVELOPING SFC LOW ALONG THE OLD
BACKDOOR FRONTAL BOUNDARY TO OUR SOUTH MAY RESULT IN SIGNIFICANT
CONVECTION ACROSS THE EASTERN GULF/FL PANHANDLE AREA...WHICH WOULD
LIMIT PCPN FURTHER NORTH ACROSS OUR CWA. LATEST GFS AND HPC GUIDANCE
SUGGEST MOST OF THE CWA WILL SEE 1.0 TO 1.5 INCHES...WITH HEAVIER
AMOUNTS CLOSER TO THE GULF COAST. DRY ANTECEDENT AIR MASS...FAST
MOVEMENT OF SYSTEM...AND POTENTIAL LIMITING FACTOR FROM DOWNSTREAM
CONVECTION SUGGESTS THAT RAINFALL AMOUNTS WILL BE MODEST. AM
REMOVING THE MENTION OF HEAVY RAIN WITH THIS PACKAGE...ALTHOUGH
PERIODS OF MODERATE RAIN LATE TONIGHT AND FRIDAY MORNING ARE LIKELY.

FINALLY...THERE STILL REMAINS SOME CONCERN FOR SEVERE IN THE SE PART
OF THE CWA. MINIMAL CAPE AND INSTABILITY STILL INDICATED ACROSS THIS
REGION OF THE CWA FRI AFTERNOON. BY THAT TIME...THIS AREA SHOULD BE
IN A WARM SECTOR. WHILE THE LLJ APPEARS TO BE FURTHER NORTH IN THE
COLD AIR AND OUT OF PHASE WITH THE BEST INSTABILITY...THERE STILL
APPEARS TO BE AT LEAST A SMALL THREAT FOR ROTATING CELLS PER SWODY2
IN THE FAR SE COUNTIES. LOCATION OF WEDGE BOUNDARY WILL BE CRITICAL
AND COULD REMAIN SOUTH OF THE CWA BORDER KEEPING THE THREAT OF TSRA
SOUTH AS WELL. AGAIN...DOWNSTREAM CONVECTION WILL PLAY A MAJOR ROLE
IN THIS AS WELL. FEEL ANY SEVERE THREAT WOULD BE FROM CELLS
EXHIBITING LITTLE OR NO LIGHTNING...BUT THERE IS ENOUGH CAPE AND
ELEVATED INSTABILITY TO SUGGEST THAT A RUMBLE OR TWO OF THUNDER
CANNOT BE RULED OUT FRI AFTN IN OUR SE COUNTIES NEAR THE SFC LOW.

UNSEASONABLY COLD TEMPS ON TAP FOR FRI AS NOTED ABOVE WITH STRONG
WEDGE...DYNAMIC COOLING...AND WETBULB EFFECT. AREAS FROM AHN-GVL
WILL STRUGGLE TO EVEN REACH 50 FRI. THE FAR S/SE AREAS SHOULD REACH
THE 60S...ESPECIALLY THE SE. MIN TEMPS TONIGHT SHOULD BE CLOSE TO
WETBULB TEMPS...MOSTLY MID 40S NE TO MID 50S SW. SAT WILL BE MUCH
MORE PLEASANT AND WARMER WITH INCREASED SUNSHINE...DESPITE BEING IN
WEAK COLD ADVECTION. MODEL GUIDANCE SIMILAR FOR MAX/MIN TEMPS
REMAINDER OF SHORT TERM PERIODS. SUN WILL BE THE WARMEST AND MOST
PLEASANT DA OF THE NEXT SEVEN IN ADVANCE OF THE NEXT STRONG FRONT
TO MOVE INTO THE AREA DURING THE EXTENDED PERIODS.

.LONG TERM /SUNDAY THROUGH THURSDAY/...
ALL STILL APPEARS TO BE ON TRACK FOR AN EXTENDED PERIOD OF DRY AND
UNSEASONABLY COOL/COLD WEATHER FOR THE LONG TERM PERIODS. STRONG
SHORT WAVE WILL DIVE RAPIDLY SE FROM THE CENTRAL CANADIAN PROVINCES
INTO THE EASTERN U.S. BY EARLY NEXT WEEK. THIS WILL RESULT IN AN
EXCEPTIONALLY DEEP...FULL LATITUDE MERIDIONAL TROUGH DIGGING INTO
THE SE U.S. BY MON. A 1046MB ARCTIC/CANADIAN HIGH DROPS SE OUT OF
CENTRAL CANADA INTO THE MID U.S. THIS IS A VERY FAVORABLE PATTERN
FOR MUCH BELOW NORMAL TEMPERATURES IN THE SE U.S. THE DRY...COOL
WEATHER SHOULD CONTINUE ALL OF NEXT WEEK AS THE UPPER TROUGH TAKES
THE ENTIRE WEEK TO SHIFT OFF THE EAST COAST AND THE LARGE SFC HIGH
TAKES FROM MON-THU TO EVEN REACH GA. TOWARD THE VERY END OF THE
EXTENDED PERIODS...A MORE ZONAL PATTERN EVOLVES...AND THERE IS A
GENERAL TREND TOWARD TROUGHING IN THE SW U.S...BUT NW FLOW ALOFT
CONTINUES OVER THE SE U.S. THROUGHOUT THE PERIOD. THE
ARCTIC/CANADIAN FRONT PASSES THROUGH THE AREA MID-DAY MON. MOISTURE
IS SCARCE...BUT SOME MID-CLOUDS WILL LIKELY OCCUR AND CANNOT RULE
OUT A FEW SPRINKLES FROM STRONG UPPER DYNAMICS. WILL KEEP POPS BELOW
15 PERCENT FOR NOW. GFS GRIDDED TEMPS ADVERTISE FREEZING TEMPS IN N
GA EACH MORNING FROM TUE-THU. STRONG COLD ADVECTION TUE WILL RESULT
IN HIGHS ONLY IN THE 50S NORTH AND LOWER 60S SOUTH...WITH WED AND
THU LIKELY THE COLDEST MORNINGS. THIS INDEED LOOKS LIKE A VERY COLD
PATTERN FOR US. THE WIND MAY INITIALLY PREVENT ANY WIDESPREAD
FREEZING TEMPERATURES...BUT RADIATIONAL CONDITIONS WILL BECOME MORE
FAVORABLE BY MID-WEEK. PREFER COLDER 00Z MEX OVER 12Z MEX...SO DO
NOT PLAN TO MAKE ANY MAJOR CHANGES TO EXTENDED TEMPS.

.AVIATION 8PM TONIGHT THROUGH 8PM FRIDAY/...
EXPECT AN EASTERLY WIND OF 10 TO 15 KTS TO PREVAIL WITH OCCASIONAL
GUSTS TO 20 KTS ON FRIDAY DUE TO PRESSURE GRADIENT BETWEEN HIGH
PRESSURE RIDGE AND LOW PRESSURE SYSTEM IN THE GULF. CURRENT VFR CIGS
WILL GRADUALLY LOWER TO MVFR AFTER 11 PM AND IFR AFTER 5AM ON FRIDAY
AS THE MOISTURE INCREASES IN ADVANCE OF THE LOW PRESSURE SYSTEM
MOVING NORTHEAST IN THE GULF. CURRENT RADAR INDICATES PATCHES OF
VIRGA MOVING NORTHEAST AT 22 KTS WITH MEASURABLE RAIN IN SE AL AND
SW GA. EXPECT LIGHT RAIN TO BEGIN IN THE CSG-MCN AREA AROUND 9
PM...ATL METRO AREA AFTER 11 PM AND AHN AFTER MIDNIGHT. VISIBILITIES
INITIALLY UNRESTRICTED UNTIL RAIN BEGINS...THEN 4 TO 6 MILES FOR
SEVERAL HOURS LOWERING TO AROUND 2 MILES ON FRIDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
ATHENS          49  52  48  71  43 /  90 100  50  10   0
ATLANTA         50  54  48  68  45 / 100 100  20  10   0
BLAIRSVILLE     45  51  45  60  38 /  90 100  50  10   0
CARTERSVILLE    50  56  46  66  38 / 100 100  20  10   0
COLUMBUS        58  64  52  73  47 / 100 100  20   0   0
GAINESVILLE     48  50  45  67  44 /  90 100  50  10   0
MACON           56  63  51  74  43 / 100 100  20   0   0
ROME            53  58  47  67  38 / 100 100  30  10   0
PEACHTREE CITY  52  55  46  68  38 / 100 100  20  10   0
VIDALIA         59  66  55  76  44 /  90 100  20   0   0

&&

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

$$

19/16

for a comprehensive glossary of weather terms used in this and other NWS products. (courtesy WFO Norman, OK)