Expires:No;;217389
FXUS63 KTOP 242343
AFDTOP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
543 PM CST TUE NOV 24 2009
.UPDATE...
UPDATE FOR 0Z AVIATION.
&&
.DISCUSSION...
SEE PREVIOUS DISCUSSION.
&&
.AVIATION...
CLOUD COVER NEARLY GONE FROM RECENT SYSTEM...WITH ATTENTION
TURNING TO THE NORTHWEST WITH THE NEXT QUICKLY MOVING UPPER TROF.
SHOULD SEE WINDS BACK OFF BY 0Z WITH THE LOSS OF HEATING AND
RELAXING GRADIENT...WITH SOME ADDITIONAL BACKING POSSIBLE
OVERNIGHT AHEAD OF THE NEXT SYSTEM. MAIN QUESTION IS FOR A FEW
HOURS OF MVFR CEILINGS DURING MIDDAY WEDNESDAY. OPPORTUNITY FOR
MOISTURE RETURN WITH FAST NATURE OF SYSTEM MAY BE SMALL ENOUGH FOR
CEILINGS TO REMAIN VFR...AND WILL PLAY THIS FOR NOW. VERY MINOR
CONCERN FOR BR DEVELOPMENT LATE TONIGHT...BUT INCREASING CLOUDS
AND DRY AIR MIXING IN SHOULD KEEP IT AT BAY DESPITE DAMP GROUND
AND A STRONG INVERSION. 
65
&&
.PREV DISCUSSION... /ISSUED 252 PM CST TUE NOV 24 2009/ 
DISCUSSION...
SHORT TERM (THROUGH WEDNESDAY)...
THE 19Z WATER VAPOR SATELLITE IMAGERY SHOWED AN INTENSE UPPER LOW 
OVER SOUTHERN IA. A SECOND UPPER LEVEL TROUGH WAS DIGGING 
SOUTH-SOUTHEAST ACROSS THE NORTHERN HIGH PLAINS.
THE 19Z SURFACE MAP SHOWED A 1000MB AREA OF LOW PRESSURE ACROSS 
SOUTH CENTRAL IA. A SFC COLD FRONT EXTENDED SOUTH ACROSS THE MS 
RIVER VALLEY BEFORE CURVING MORE TO THE SOUTHWEST ACROSS LA. A SFC 
RIDGE WAS LOCATED ACROSS THE SOUTHERN HIGH PLAINS. WRAP AROUND LOW 
CLOUDS ACROSS THE EASTERN COUNTIES OF THE CWA...EVEN SOME DRIZZLE 
ACROSS THE EXTREME NORTHEAST COUNTIES...WILL SLOWLY PUSH EAST 
THROUGH THE LATE AFTERNOON AND EARLY EVENING HOURS. CLEAR SKIES 
ACROSS THE WESTERN TWO THIRDS OF THE CWA WILL MOVE EAST ACROSS THE 
ENTIRE CWA LATER THIS EVENING. AS THE SFC LOW MOVES EAST INTO THE 
GREAT LAKES STATES...THE SFC PRESSURE GRADIENT ACROSS CENTRAL AND 
EASTERN KS WILL WEAKEN AND CAUSE THE NORTHWEST SFC WINDS TO DIMINISH 
AFTER SUNSET.
TONIGHT...SKIES WILL CLEAR ACROSS THE ENTIRE CWA THROUGH THE EVENING 
HOURS. THE 5H TROUGH OVER THE NORTHERN HIGH PLAINS WILL DIG 
SOUTHEAST AND AMPLIFY AS IT MOVES SOUTHEAST INTO EASTERN NE. THERE 
MAY BE ENOUGH ASCENT AHEAD OF THE UPPER LEVEL TROUGH AXIS FOR 
SPRINKLES OR FLURRIES TO DEVELOP ACROSS THE NORTHERN AND WESTERN 
COUNTIES LATE TONIGHT AND THROUGH THE EARLY MORNING HOURS OF 
WEDNESDAY. THE LOW-LEVELS OF THE ATMOSPHERE LOOK TOO DRY TO SUPPORT 
ANY MEASURABLE PRECIP. MID AND HIGH LEVEL CLOUDS WILL INCREASE FROM 
NORTHWEST TO SOUTHEAST ACROSS THE CWA LATER TONIGHT AHEAD OF THE 
APPROACHING UPPER LEVEL TROUGH. OVERNIGHT LOWS WILL BE IN UPPER 20S 
WEST TO LOWER 30S EAST.
WEDNESDAY...THE UPPER TROUGH AXIS WILL PASS SOUTHEAST OF THE AREA BY 
NOON BRINGING AN END TO ANY SPRINKLES OR FLURRIES DURING THE MID AND 
LATE MORNING HOURS. LOW-LEVEL CAA WILL CAUSE A SFC RIDGE TO BUILD 
SOUTHEAST ACROSS THE CENTRAL AND SOUTHERN PLAINS. THE HIGH AND MID 
CLOUDS WILL DURING WILL SHIFT SOUTHEAST OF THE AREA WITH MOSTLY 
SUNNY SKIES DEVELOPING THROUGH THE AFTERNOON HOURS. EVEN WITH 
INSOLATION DURING THE AFTERNOON. THE LOW-LEVEL CAA WILL KEEP HIGHS 
IN THE MID TO UPPER 40S. THE INCREASING NORTHWEST WIND AT 15 TO 20 
MPH WITH GUSTS TO 30 MPH WILL MAKE IT FEEL EVEN COOLER.
GARGAN
LONG TERM (THURSDAY THROUGH TUESDAY)...
THE MID RANGE FORECAST FROM TUESDAY THROUGH THE FIRST PART OF
SATURDAY APPEARS THAT IT WILL BE QUITE TRANQUIL. MODEL AGREEMENT
IS STRONG DURING THIS TIME PERIOD BOTH IN TERMS OF SENSIBLE
WEATHER AND THE OVERALL PATTERN OVER THE CENTRAL PLAINS. THE MAIN
FORECAST POINTS DURING THIS PERIOD INVOLVE HIGH AND LOW
TEMPERATURES THURSDAY AND FRIDAY. ANTICIPATE HIGH PRESSURE TO
CENTER JUST WEST OF THE CWA THURSDAY MORNING. THE BOUNDARY LAYER
WILL LIKELY DECOUPLE WITH WINDS SHARPLY DIMINISHING OVERNIGHT.
SINKING AIR AND PERSISTENT COLD AIR ADVECTION FOR THE 36+ HOURS
LEADING UP TO THIS POINT WILL LIKELY ALLOW THURSDAY MORNING
TEMPERATURES TO BE QUITE COOL IN THE LOWER TO MID 20S. WOULD NOT
BE SURPRISED TO SEE SOME LOCATIONS GET COLDER YET DEPENDING JUST
WHERE THE HIGH PRESSURE CENTERS UP. SHOULD BEGIN TO GET A BIT OF
RETURN FLOW BY LATE THURSDAY BUT WILL DECOUPLE AGAIN BY FRIDAY
MORNING WITH COOL TEMPERATURES EXPECTED...ALBEIT NOT AS COOL AS
THURSDAY MORNING. FRIDAY LOOKS TO BE QUITE NICE WITH WARM AIR
ADVECTION BRINGING TEMPS UP INTO THE 50S AND 850 TEMPS UP IN THE
TEENS. 
THINGS BEGIN TO TURN ON SATURDAY AS TWO PIECES OF ENERGY BEGIN TO
MAKE THEIR PLAY. THIS IS ALSO THE POINT WHERE MODEL SOLUTIONS
DIVERGE SIGNIFICANTLY. THE MAIN POINT OF CONTENTION IS IN THE
SPLITTING OF A STRONG SHORT WAVE TROUGH AS IT MOVES OUT OF THE
GULF OF ALASKA. ALL MODELS CURRENTLY DO SPLIT THE ENERGY WITH ONE
LOW SKIRTING ACROSS THE NORTHERN TIER WHILE THE SECOND DROPS SOUTH
INTO THE SOUTHWEST US. THE DIFFERENCES COME IN THE STRENGTH OF
EACH PIECE OF ENERGY...AND THIS JUST HAPPENS TO HAVE A SIGNIFICANT
IMPACT ON OUR SENSIBLE WEATHER. CURRENTLY THE PREFERRED MODEL IS
THE ECMWF WHICH IN COMPARISON TO THE GFS SUITE...KICKS MORE
ENERGY INTO THE SOUTHERN WAVE...CLOSES IT OFF OVER THE SOUTHWEST
AND MORE SLOWLY BRINGS THE UPPER SYSTEM ACROSS THE PLAINS. THE
REST OF THIS DISCUSSION SHOULD BE READ WITH THE FACT IN MIND THAT
THE LEVEL OF UNCERTAINTY IN THE OVERALL SYSTEM IS RELATIVELY HIGH.
NOW IN TERMS OF THE SENSIBLE WEATHER DURING THE PERIOD FROM LATE
SATURDAY THROUGH TUESDAY...ONCE AGAIN...SIGNIFICANT VARIABILITY IS
POSSIBLE. A COLD FRONT WILL LIKELY PUSH INTO KANSAS DURING THE DAY
ON SATURDAY AS THE NORTHERN STREAM ENERGY PUSHES COLD AIR DOWN
ACROSS THE NORTHERN PLAINS IN ITS WAKE. DESPITE THE FRONTAL
PASSAGE...THIS FRONT LOOKS TO BE FAIRLY DRY INITIALLY AS MOISTURE
RETURN WILL NOT SIGNIFICANTLY AMPLIFY UNTIL SOMETIME ON SATURDAY
NIGHT WHEN THE SOUTHERN STREAM ENERGY BEGINS TO EJECT ACROSS THE
ROCKIES. AT THIS POINT...EXPECT PRECIP TO BEGIN ACROSS THE AREA
SAT NIGHT WITH THE BEST CHANCES DURING THE DAY ON SUNDAY. AND...
IN HONESTY...PRECIP CHANCES LOOK PRETTY GOOD FOR SOMEWHERE IN THIS
TIME FRAME. THE SYSTEM SHOULD HAVE A BROAD WARM SECTOR WITH MOIST
FLOW OVER RUNNING A SHALLOW COLD FRONT AND PRODUCING A BROAD AREA
OF PRECIP WHILE BEST UPPER LEVEL DYNAMICS LOOK TO IMPACT THE
REGION LATER ON SUNDAY. 
HERE IS WHERE THINGS GET VERY COMPLICATED...IN THE FORECASTING OF
PRECIP TYPE. CURRENTLY WENT WITH THE EVENT BEGINNING AS RAIN AND
THEN INTRODUCING THE CHANCE OF SNOW MIXING IN FAIRLY EARLY IN THE
EVENT. NATURALLY MUCH OF THIS DEPENDS ON THE EVENTUAL STORM TRACK.
IT DOES APPEAR LIKELY THAT NORTHERN ZONES OF THE SYSTEM WILL SEE A
GOOD CHANCE OF SNOW WHILE THE WARM SECTOR WILL LIKELY SEE A GOOD
BIT OF RAIN. ONE QUESTION IS IN JUST HOW COLD THE POST FRONTAL AIR
WILL BE. APPEARS THAT IT WILL HAVE A SOURCE REGION WELL INTO
CANADA. THE COARSER GRID MODELS TEND TO OVER FORECAST TEMPERATURES
IN THIS SORT OF SITUATION WITH A SHALLOW COLD FRONT. THAT SAID...
IT SHOULD BE NOTED THAT IF SURFACE TEMPERATURES END UP BEING
SIGNIFICANTLY COOLER THAN FORECAST...IT MAY EVEN POINT TOWARD
THE POSSIBILITY OF ICE EARLY IN THE EVENT WITH THE STRONG WARM
NOSE AND MOISTURE ADVECTION. THAT SAID...THIS DOES NOT CURRENTLY
LOOK LIKE A STRONG POSSIBILITY AS EVEN THE CANADIAN AIR IS
SEASONABLY WARM AT THE MOMENT.
BARJENBRUCH
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.TOP WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$