FXUS63 KLSX 261202
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
602 AM CST SAT DEC 26 2009

.DISCUSSION...
/426 AM CST SAT DEC 26 2009/

THE DOUBLE LOW STRUCTURE THAT WAS PRESENT IN THE UA FIELD OVER THE 
CENTRAL U.S. CHRISTMAS EVE AND CHRISTMAS DAY HAS NOW CONGEALED INTO
ONE SYSTEM THAT I THINK CAN ONLY BE DESCRIBED AS MASSIVE...AND AS
NOTED BY THE SHORT TERM DESK IT IS IMPACTING ALMOST ALL OF THE
CONUS WITH THE EXCEPTION OF THE PACIFIC NW...AND A FEW NEW ENGLAND
STATES. THE RESULTANT CIRCULATION CENTER IS WOBBLING ITS WAY NWD
THROUGH THE MID MISSISSIPPI VALLEY...AND SHORT RANGE MODELS ARE
FORECASTING SEVERAL SHORTWAVES TO ROTATE AROUND THIS FEATURE OVER
THE NEXT 36 HOURS. ONE SUCH FEATURE CAN BE SEEN ON THE WATER VAPOR
SATELLITE IMAGERY EARLY TODAY OVER NORTHERN KS...WITH A SECOND AND
STRONGER SHORTWAVE EXTENDING FROM CENTRAL IA INTO EASTERN NE...AND
YET A THIRD FROM NE IA INTO S MN.

OVERALL WEATHER TREND FOR OUR CWA SHOULD BE FOR THESE SHORTWAVES TO 
GENERATE OCCASIONAL PERIODS OF LIGHT SNOW THROUGH TONIGHT...WITH THE 
GREATEST POPS OVER NORTHERN SECTIONS OF THE CWA WHERE THE DYNAMICS 
ASSOCIATED WITH EACH SHORTWAVE WILL BE THE STRONGEST.  NOT 
ANTICIPATING ANY LARGE SNOWFALL TOTALS...BUT THE SEVERAL ROUNDS OF 
PRECIPITATION SHOULD ADD UP TO ADD TO THE SNOW THAT FELL ON 
CHRISTMAS DAY.  BEST ESTIMATE FROM THE CONSENSUS OF MODEL QPFS IS 
THAT SNOWFALLS WILL RANGE FROM 1-2 INCHES OVER NW THIRD OF OUR 
CWA...GENERALLY ALONG AND NORTH OF A COU-PPQ LINE...WITH LESSER 
ACCUMULATIONS ELSEWHERE.  HAVE UPPED POPS OVER MUCH OF THE AREA ON 
SUNDAY AS MODELS ARE SUGGESTING ONE LAST SHORTWAVE WILL SWING 
THROUGH AS UPPER LOW FINALLY BEGINS TO MOVE EAST. ADDITIONAL MINOR 
ACCUMULATIONS COULD OCCUR WITH THIS FEATURE AS WELL...BUT FOR THE 
TIME BEING HAVE KEPT POPS IN THE CHANCE CATEGORY. 

TEMP TRENDS ARE GOING TO BE RATHER TRICKY TODAY. STRONG MIXING AND A
BIT OF WAA HAS PRODUCED STEADY OR SLOWLY RISING TEMPS ACROSS MUCH
OF THE AREA DURING THE PREDAWN HOURS. HOWEVER...PERSISTENT CLOUD
COVER AND OCCASIONAL PRECIPITATION...AND A RETURN OF WEAK CAA...SHOULD
KEEP TEMPS FROM WARMING MUCH SO HAVE TRENDED TOWARD THE COOLER
MET MOS. EXCEPTION MAY BE IN THE FAR SE COUNTIES OF THE CWA WHICH
IS ON THE FRINGES OF THE CLOUD COVER FOR A BIT EARLY TODAY...AND
HAVE GONE A BIT WARMER IN THESE AREAS. PERSISTENT CLOUDINESS
SHOULD FAVOR A LIMITED DIURNAL TEMP SWING TONIGHT-SUN...AND
BECAUSE OF THIS FAVORED THE COOLER MET NUMBERS FOR SUNDAYS HIGHS.

DRY WEATHER SHOULD RETURN TO THE AREA FOR THE START OF THE WORK
WEEK...WITH A SLOW MODERATION IN TEMPERATURES.

TRUETT

&&

.AVIATION...
/546 AM CST SAT DEC 26 2009/

FOR THE 12Z TAFS...
PRIMARY CONCERNS FOR AVIATION INTERESTS TODAY WILL BE PERIODS OF
LIGHT SNOW ASSOCIATED WITH TWO UPPER LEVEL SHORTWAVE TROFS
ROTATING AROUND THE MAIN LOW PRESSURE SYSTEM OVER THE MIDWEST. THE
ONSET OF THE SNOW IN THE TERMINAL FORECASTS IS BASED ON A
COMBINATION OF THE RUC MODEL AND WATER VAPOR SATELLITE PICS...AND THE
FORECAST FLIGHT CONDITIONS ARE BASED ON CURRENT OBSERVATIONS
UNDERNEATH THESE SHORTWAVES. LOOKS LIKE IFR VSBYS ARE A GOOD BET
WITH LOW MVFR CIGS. I CHOSE TO HOLD OFF ON THE LOWEST CONDITIONS
UNTIL LATER IN THE FORECAST WHEN THE SECOND SHORTWAVE ROTATES DOWN
OUT OF IOWA TO JOIN FORCES WITH THE FIRST WAVE MOVING EAST OUT OF
KANSAS SINCE ANY IFR CONDITIONS SEEM TO BE HAVING A LOT OF
TROUBLE PENETRATING TOO FAR INTO CENTRAL AND EASTERN MISSOURI OVER
THE PAST 6-10HRS. THO IT IS CERTAINLY POSSIBLE WE'LL SEE THE IFR
VSBYS EARLIER THAN CURRENT TERMINALS INDICATE.

CARNEY

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&

$$

WFO LSX