FXUS63 KTOP 040504
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1104 PM CST THU DEC 3 2009

.UPDATE...UPDATED FOR 06Z AVIATION.

&&

.AVIATION...VFR THROUGH THE PD. SOME SCT CLOUDS CAN BE EXPECTED IN
THE AFTERNOON THEN CLEAR SKIES WILL ONCE AGAIN PREVAIL. WIND WILL
SHIFT TO THE WEST AOB 10KTS.

SALLY
&&

PREV DISCUSSION... /ISSUED 332 PM CST THU DEC 3 2009/ 

DISCUSSION...

COLD UPPER TROF WAS OVER THE NORTHERN PLAINS THIS MORNING WITH -40C 
TEMPS AT 500MB AND -14C AT 850MB. DEEP CYCLONIC FLOW BRINGING BATCHES 
OF STRATUS AND STRATOCU THROUGH...WITH SOME FLURRIES IN THE DEEPER 
MOISTURE IN THE NORTHEAST. 21Z DEWPOINTS WERE IN THE 9-14F RANGE 
WITH GUSTY WINDS PERSISTING IN THE MIXED LOWER MILE OR SO OF THE 
ATMOSPHERE.  

WINDS WILL SLACKEN EARLY THIS EVENING AS THE BOUNDARY LAYER 
DECOUPLES...BUT WINDS JUST ABOVE STAY IN THE 15-20KT RANGE. DESPITE 
THE DRY AIR AND SOME CLEARING OF THE LOW CLOUD...TEMPS MAY STRUGGLE 
TO FALL TOO FAR...AND MOS SEEMS TO HAVE PICKED UP ON THIS. WILL BUMP 
UP LOWS A BIT. LOW LEVEL WINDS BACK FOR SOME WEAK WARM AIR ADVECTION 
TO RESULT IN SLIGHTLY WARMER TEMPS FOR FRIDAY. 

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AFTER A COLD NIGHT FRIDAY NIGHT SATURDAY WILL SEE TEMPERATURES 
REBOUND BACK ONLY INTO THE MID 40S AS WARM ADVECTION OCCURS AHEAD OF 
A DEEPENING LOW IN THE LEE OF THE ROCKIES. AN ADVANCING MID LEVEL 
WAVE WILL MOVE THROUGH THE ROCKIES AND INTO THE PLAINS ON SUNDAY. 
THE BEST LIFT APPEARS TO BE CONCENTRATED ACROSS THE NORTHERN 
COUNTIES THEN NORTHWARD INTO NEBRASKA. ISENTROPIC LIFT WILL OCCUR 
AHEAD OF THE APPROACHING WAVE ON SUNDAY AS WELL BUT AGAIN THE FOCUS 
IS IN THE NORTHEAST PART OF THE CWA INTO IOWA. FORECAST SOUNDINGS 
STILL SUGGEST SATURATION OF THE SNOW CRYSTAL GROWTH REGION ACROSS 
THE WESTERN CWA AND THEN ACROSS THE NORTH. THE EAST CENTRAL DOES NOT 
SATURATE IN THE SNOW GROWTH REGION AND COULD SEE MAINLY DRIZZLE OR 
NO PRECIPITATION  THERE UNTIL PERHAPS SUNDAY EVENING BETWEEN 
03Z AND 06Z. AFTER 06Z LIFT MOVES AWAY. 

COLD FRONT MOVES IN BEHIND THE WAVE ON SUNDAY NIGHT WITH COLD ARCTIC 
AIR BUILDING INTO THE PLAINS WITH A SURFACE HIGH BUILDING INTO THE 
PLAINS THROUGH MONDAY. THIS COLD AIR WILL REMAIN IN PLACE THROUGH 
MUCH OF NEXT WEEK. A MORE POTENT STORM SYSTEM WILL BEGIN TO 
AFFECT THE PLAINS MONDAY NIGHT THROUGH TUESDAY NIGHT. OPERATIONAL 
RUNS OF THE GFS...GEM AND ECMWF HAVE SOME DIFFERENCES WITH THE MID 
LEVEL FEATURES. THE GFS IS MORE PHASED WITH THE NORTHERN AND 
SOUTHERN STREAMS WHILE THE ECMWF IS FURTHER NORTH THAN THE GFS. THE 
12Z GFS MEAN HAS TRENDED TOWARD THE 00Z ECMWF WITH THE STRONGER MID 
LEVEL FEATURES AND MORE NORTHERLY. GOOD DEEP LAYER FRONTOGENESIS IS 
FORECAST ACROSS MUCH OF THE CWA ON TUESDAY. INITIAL ISENTROPIC LIFT 
MONDAY NIGHT AND EARLY TUESDAY WILL BRING SOME SNOWS BEFORE THE 
FRONTOGENESIS AND SYNOPTIC SCALE LIFT INCREASES ON TUESDAY. TRACK OF 
THE SURFACE LOW OUT OF THE PANHANDLE WILL MAKE FOR A BAND OF SNOW 
SOMEWHERE ACROSS THE CWA. GIVEN THE LIKELIHOOD OF CHANGES AS THE 
SYSTEM DEVELOPS WILL LEAVE PRECIPITATION CHANCES IN THE CHANCE RANGE 
FOR NOW...BUT DID INCREASE SOME OVER THE PREVIOUS FORECAST. WENT 
COLDER THAN GUIDANCE TUESDAY NIGHT THROUGH WEDNESDAY WITH COLD AIR 
MOVING INTO THE REGION TUESDAY NIGHT AND WEDNESDAY BEFORE SHUNTING 
OFF TO THE EAST ON THURSDAY.

53

&&

.TOP WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

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