FXUS64 KOHX 241101
AFDOHX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
501 AM CST THU DEC 24 2009

.UPDATE...

UPDATE FOR 12Z TAF DISCUSSION.

&&

.AVIATION...

12Z TAFS...MAIN CONCERN WILL BE WINDS. DEEPENING LOW PRESSURE OVER
THE MS VALLEY WILL GENERATE STRONG SOUTH TO SOUTHEAST WINDS
THROUGH THE NEXT 24 HOURS. WIND GUSTS TO 30KT POSSIBLE BY
16Z...THEN TO 40KT BY 00Z. WINDS TO 50KT WILL BE PRESENT AT
1500KFT BY 00Z. WINDS WILL BE FROM AROUND 140 DEGREES UNTIL
FRONTAL PASSAGE LATE TONIGHT...SHIFTING TO 200.

CIGS AND VSBYS WILL BE MAINLY VFR THROUGH TODAY
WITH OCNL -SHRA. CIGS AND VSBYS DOWN TO MVFR AFTER 00Z...WITH A
BRIEF PERIOD OF IFR POSSIBLE FROM 02Z-09Z IN DOWNPOURS JUST AHEAD
OF OCCLUDED FRONTAL PASSAGE.

13/SH

&&

.PREV DISCUSSION... /ISSUED 331 AM CST THU DEC 24 2009/ 

DISCUSSION...
FORECAST REASONING WILL BE BASED ON A LEAN TOWARD THE MODEL CONSENSUS
SOLUTION FOR THE FORECAST PERIOD UNLESS OTHERWISE NOTED.

CURRENTLY...LIGHT RAINFALL MOVING ACROSS LOCATIONS GENERALLY W OF
I-65. MAIN SWATH OF RAINFALL STILL ACROSS THE MS RIVER VALLEY 
REGION. OTHERWISE...CLOUDY SKIES...TEMPS IN THE UPPER
40S TO LOWER 50S...DEWPOINTS SPANNING THE 40S...WITH SELY WINDS
AROUND 10 TO 15 MPH. MAIN SFC LOW CENTERED ACROSS E TX...WITH COLD
FRONT POSITIONED FROM LOW CENTER NEWD INTO W MO...AND A SFC TROUGH
SW TO NE ACROSS THE THE MID STATE. TIGHTENING SFC PRESSURE GRADIENT
NOTED E-W ACROSS THE REGION. PRONOUNCED SWLY FLOW ALOFT IN
ASSOCIATION WITH DIGGING UPPER LEVEL CLOSED LOW ACROSS EASTERN
PLAINS OF NM.        

FORECAST QUANDARIES...EXPECT SFC/UPPER LEVEL LOWS TO BE IN THE 
VICINITY OF THE CNTRL AR/MO BORDER BY 00Z FRI...AND CONTINUE MOVING 
NEWD AND DRAG FRONT ACROSS THE ENTIRE MID STATE BY 06Z FRI. WITH 
THIS IN MIND...AND CURRENT BOUNDARY LAYER MOISTURE REMAINING 
RELATIVELY DRY THRU 00Z FRI...HAVE CUT BACK ON POPS W-E TODAY. AM 
STILL GOING TO INCLUDE ISOLATED TSTMS THIS AFTERNOON W AND CNTRL AND 
ACROSS THE ENTIRE MID STATE TONIGHT THRU 06Z...BUT MODELS SHOWING
THIS BEING A VERY MARGINAL SITUATION AT BEST...AND WOULD NOT BE
SURPRISED IF THE TSTMS THAT DUE DEVELOP ARE GOING TO BE FEW AND
FAR BETWEEN. THOSE TRAVELING INTO AND OUT OF THE MID STATE BETWEEN
06Z AND 12Z FRI SHOULD EXPERIENCE ONLY LIGHT RAINFALL...WITH THE
POTENTIAL OF A RAIN/SNOW MIX AS ONE APPROACHES THE TN RIVER
VALLEY...BUT NO ACCUMULATIONS ARE EXPECTED.

AS FOR THE WIND ADVISORY...WILL CONTINUE WITH TIMING OF 15Z TODAY
THRU 06Z FRI...AS SFC PRESSURE GRADIENT WILL CONTINUE TO TIGHTEN
AS FRONT APPROACHES LOCATIONS ACROSS THE MID STATE.  

SAT THRU SUN...THE STRONG SURFACE LOW WILL BE LOCATED OVER THE IL-IA 
AREA AND IS FORECAST TO MOVE SLOWLY NE ACROSS THE W 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 PCPN. DUE HOWEVER BELIEVE THAT THERE WILL
BE ENOUGH MOISTURE AROUND TO SUPPORT AT LEAST MOCLDY SKIES DURING
THIS PERIOD. 

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 CONTINUES TO HAVE MORE AMPLITUDE 
WITH THE UPPER LEVEL RIDGE...WHEREAS THE GFS MODEL CONTINUES TO 
FLATTEN IT OUT.

TUE NIGHT THRU THU...GFS AND ECMWF ARE BECOMING MORE IN LINE WITH 
CHANCES OF PCPN...ALTHOUGH THE ECMWF DEVELOPS THE PCPN SCENARIO
STILL MORE PREDOMINATELY. ECMWF SHOWING SHORTWAVE NOW APPROACHING THE
MID STATE LATER ON WED...AND NOT COMPLETELY MOVING THRU THE REGION
UNTIL SOMETIME ON THU. GFS CONTINUES TO SHOW THE BEST CHANCE OF PCPN 
S OF THE MID STATE. WOULD LIKE ANOTHER MODEL RUN FOR ADDITIONAL
CLARIFICATION ON THE TIMING AND TO SEE IF GFS PICKS UP ON THIS 
POSSIBLE SHORTWAVE PASSAGE BEFORE MAKING ANY CHANGE TO CURRENT 
FORECAST PACKAGE THRU THIS TIME PERIOD.   

FOR TEMPS...BUT WILL GENERALLY GO CLOSE TO GFS MOS NUMBERS THRU 
SAT...WITH NECESSARY ADJUSTMENTS TO MEX MOS NUMBERS WHERE NEEDED
FOR REMAINDER OF FORECAST PERIOD. 

THANKS FOR COORDINATION LMK AND MEG.

31/JBW

&&

.PRELIMINARY POINT TEMPS/POPS...
NASHVILLE      56  37  43  29 /  50 100  20  10 
CLARKSVILLE    56  36  41  28 /  70 100  20  10 
CROSSVILLE     54  38  39  26 /  40 100  20  10 
COLUMBIA       58  37  43  29 /  50 100  20  10 
LAWRENCEBURG   58  37  42  28 /  60 100  20  10 
WAVERLY        56  36  42  29 /  70 100  20  10 

&&

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

&&

$$