FXUS64 KOHX 240100
AFDOHX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
700 PM CST WED DEC 23 2009

.UPDATE...
SEE AVIATION DISCUSSION.

&&

.AVIATION...
AREA OF PCPN IN W TN MOVG NE. SCT RW- W OF I-65 THIS EVENING.
LITTLE CHANGE E WITH DRIER AIR. VCSH KBNA TIL MIDNIGHT. 

SFC LOW PRES MOVES N TNGT W/DEEPER MOISTURE NEAR THE LOW. SHOWERS
WL MOVE INTO MID TN THU AFTERNOON W/PREFRONTAL TROUGH AS LOW
OCCLUDES.

&&

.PREV DISCUSSION... /ISSUED 344 PM CST WED DEC 23 2009/ 

DISCUSSION...
THANKS TO SOMEWHAT DRY LOWER LEVELS...PRECIP IS HAVING A HARD TIME 
ADVANCING NE INTO THE MID STATE THIS AFTERNOON. THIS SITUATION WILL 
CHANCE LATER TONIGHT AS THE LOWER LEVELS MOISTURE IN ADVANCE OF A 
DEVELOPING STORM SYSTEM...CURRENTLY ORGANIZING OVER THE TX AREA.

ONCE THE ASSOCIATED STRONG UPPER LEVEL LOW CURRENTLY OVER NM
MOVES E AND INTO TX AREA LATER TONIGHT...IT WILL BEGIN TAKING ON
A NEGATIVE TILT. THE SURFACE LOW WILL THEN BEGIN DEVELOPING RAPIDLY.

RAIN WILL OVERSPREAD THE AREA OVERNIGHT FROM SW TO NE...WITH HIGHEST 
CHANCES IN W SECTIONS WHERE GREATEST DEPTH OF MOISTURE WILL BE  
LOCATED. THE SURFACE LOW WILL MOVE NE FROM TX AND INTO AR ON THU...
WHERE IT WILL CONTINUE TO STRENGTHEN.

ALL MODELS INCLUDING GFS ENSEMBLE AND SREF...FORECAST ANOTHER
UPPER LEVEL LOW MOVING SE AND BECOMING IN PHASE WITH THE UPPER LOW
MENTIONED PREVIOUSLY. THIS WILL ACT TO STRENGTHEN THE ENTIRE SYSTEM.
IT WILL ALSO RESULT IN A STRONG LOW LEVEL PRESSURE GRADIENT
DEVELOPING ACROSS OUR AREA BY THU MORNING AND CONTINUING INTO THU
NIGHT. THE CURRENT WIND ADVISORY WILL BE LEFT AS IS AT THIS TIME. 

SHOWALTER STABILITY INDICES WILL LOWER TO SINGLE DIGITS WHICH 
INDICATES THAT A FEW THUNDERSTORMS MAY OCCUR ON THU AND INTO EARLY 
THU NIGHT. THE ASSOCIATED COLD FRONT WILL MOVE RAPIDLY FROM SW TO NE 
ACROSS THE MID STATE THU NIGHT. THIS WILL BRING AN END TO THE
PRECIP...AND USHER IN COLDER AIR THU NIGHT AND FRI.

SAT THRU SUN...THE STRONG SURFACE LOW WILL BE LOCATED OVER THE 
IL-IA AREA AND IS FORECAST TO MOVE SLOWLY NE ACROSS THE WESTERN
GREAT LAKES REGION AND INTO SE CANADA. A RIDGE OF HIGH PRESSURE
WILL BE LOCATED N-S ACROSS THE PLAINS STATES. THE MID STATE WILL
BE UNDER COLD ADVECTION...WITH SOME LOW LEVEL WRAP AROUND MOISTURE
OF INSUFFICIENT DEPTH FOR ANY CHANCE OF PRECIP.

THE PATTERN WILL ONLY SLOWLY CHANGE MON AND TUE...WITH THE PLAINS
SURFACE RIDGE GRADUALLY SHIFTING E...AND THE UPPER LEVEL RIDGE
AXIS MOVING INTO OUR AREA. ECMWF MODEL HAS MORE AMPLITUDE WITH THE
UPPER LEVEL RIDGE...WHEREAS THE GFS MODEL FLATTENS IT OUT.

TUE NIGHT AND WED...GFS AND ECMWF GO THEIR SEPARATE WAYS REGARDING 
CHANCES OF PRECIP. ECMWF DEVELOPS AN UPPER LEVEL TROUGH AND
FORECASTS A SHORT WAVE TO APPROACH THE MID STATE TUE NIGHT AND
MOVE ACROSS THE AREA ON WED. GFS FORECASTS FLATTER FLOW...WITH
ONLY A SUBTLE INDICATION OF THIS HAPPENING. AT THIS TIME WILL
CONTINUE WITH A CHANCE OF PRECIP ON WED.

TEMPS WILL BE TRICKY TO FORECAST THROUGH MUCH OF THE PERIOD. EITHER 
MOS APPEARS A BIT TOO LOW ON OVERNIGHT LOWS TONIGHT...SO RAISED A 
TAD. 

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 9 AM THURSDAY TO MIDNIGHT CST THURSDAY NIGHT 
FOR TNZ005>011-022>034-056>066-075-077>080-093>095.

&&

$$

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