FXUS63 KTOP 232137
AFDTOP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
337 PM CST WED DEC 23 2009
.DISCUSSION...
.TONIGHT THROUGH FRIDAY...
CONSENSUS ON EXACT LOW TRACK AND STRENGTH BEGINNING TO FORM...BUT
DIFFERENCES IN NAM...GFS...SREF...AND ECMWF STILL MAKE DETAILS
DIFFICULT. WHAT I AM CONFIDENT IN IS A HIGH IMPACT EVENT DUE TO SNOW
AND BLOWING SNOW ACROSS THE AREA ON A VERY BUSY TRAVEL DAY. GIVEN
THE DEGREE OF POTENTIAL IMPACT...ISSUED A WINTER STORM WARNING FOR
THE ENTIRE AREA AND WILL LET DETAILS SORT THEM SELVES OUT AS STORM
LOOMS CLOSER.
PREVIOUS FORECAST HAD NICE POSITION OF MAIN SNOW FALL. GIVEN MY
RELIANCE ON NAM FOR UPPER MASS FIELDS AND THE NAMS PLACEMENT ON THE
WESTERN EDGE OF THE SREF ENVELOPE...I DID ADJUST SNOW AMOUNTS UP
SLIGHTLY AND EXPANDED THE SIX PLUS AREA WESTERLY TO INCLUDE MOST OF
THE CWA. I AM ONLY MODERATELY CONFIDENT IN SNOW AMOUNTS OVERALL AS
WARM AIR MAKES IT DIFFICULT TO DECIDE ON A SNOW RATIO...AND SUBTLE
DIFFERENCES IN LOW PLACEMENT WILL MAKE EXACT CHANGEOVER TIME
DIFFICULT TO PIN DOWN.
SNOW AMOUNTS WERE ARRIVED AT BY CONSENSUS OF HPC GUIDANCE AND
SURROUNDING OFFICE INPUT. PLENTY OF LIFT IN AND AROUND NEGATIVELY
TILTED TROF. HAVE NOT GOTTEN REAL EXCITED ABOUT A SIGNIFICANT HEAVY
SNOW BAND AS OF YET. IT IS A WAYS OUT IN TIME YET. ONLY AREA WHERE
THERE APPEARS TO BE AN AREA OF SUSTAINED INSTABILITY ALOFT IS IN
EXTREME NORTHEAST KANSAS. THIS IS ALSO THE AREA WHERE I HAVE PLACED
THE GREATEST SNOW AMOUNTS...AND WILL MONITOR THE EVOLUTION OF THIS
ELEVATED INSTABILITY FOR FURTHER REFINEMENT.
BASED ON 12 UTC BUFR SOUNDINGS FROM NAM AND THE GFS...REMOVED MOST
OF THE FREEZING RAIN FROM THE GRIDS. COLUMN REMAINS VERY WELL
SATURATED AND PLENTIFUL FREEZING NUCLEI EXIST. IF LOW MOVES ON
EXPECTED TRACK...WARM AIR WILL LIKELY REMAIN EAST OF THIS AREA. ONE
EXCEPTION IS FAR NE KANSAS...WHERE WARM AIR DOES EXTEND INTO LOWER
LEVELS TOMORROW MORNING INTO AFTERNOON. BECAUSE OF THIS...I DID
START THE WINTER STORM WARNING ALONG THE NORTHERN TIER OF KANSAS
COUNTIES EARLIER THAN I WOULD HAVE HAD IT BEEN ALL SNOW.
LIGHT SNOW WRAPPING AROUND UPPER LOW WILL GRADUALLY TAPER OFF INTO
FRIDAY NIGHT AND EARLY SATURDAY AS THE SYSTEM SLOWLY PULLS AWAY.
WILL TAPER ADDITIONAL SNOW AMOUNTS FROM NEAR AN INCH IN THE FAR
NORTHEAST CORNER DOWN TO A DUSTING IN THE FAR SOUTHWEST. WILL KEEP
TEMPS COLD WITH GRADUALLY DIMINISHING WINDS BY LATE SATURDAY. LOWS
SATURDAY AND SUNDAY MORNINGS WILL GENERALLY BY IN THE 5 TO 12 ABOVE
RANGE. HOWEVER...WINDCHILLS BOTH FRIDAY AND SATURDAY NIGHTS
WILL COMMONLY BE IN THE ZERO TO 10 BELOW RANGE.
AS THE UPPER SYSTEM SLOWLY PULLS AWAY OVER THE WEEKEND...THE CENTRAL
PLAINS WILL GO FROM NORTHWEST FLOW TO UPPER RIDGING PRIOR TO THE
ARRIVAL OF THE NEXT UPPER TROUGH BY MID WEEK. THIS WARRANTS KEEPING
A DRY FCST GOING FROM SUNDAY THROUGH EARLY NEXT WEEK AS THE AREA IS
IN BETWEEN SYSTEMS. WITH EXPECTED SNOWCOVER AND LITTLE IR ANY
WAA...HIGHS WILL REMAIN NEAR OR BELOW FREEZING...MAINLY IN THE 20S
SUNDAY AND MONDAY WITH ONLY SLIGHT MODERATION IN THE UPPER 20S AND
LOWER 30S FOR TUESDAY AND WEDNESDAY. MODELS CONTINUE TO KEEP THE MID
WEEK TROUGH MAINLY SOUTH OF THE CWA. THIS FAR OUT...WILL KEEP
WEDNESDAY DRY FOR NOW...AND SEE HOW MODELS HANDLE THIS WITH TIME.
63
&&
.AVIATION...
DIFFICULT FORECAST CONTINUES. CONVECTION FIRED OVER SE KS THIS
MORNING RESULTING FROM A SMALL UPPER WAVE QUICKLY MOVING THROUGH
THE AREA AS EVIDENCED BY WATER VAPOR IMAGERY AND A WARM FRONT
MOVING NORTH. EXPECT CONVECTION TO DIMINISH ONCE THIS WAVE MOVES
THROUGH BY 20/21Z. SEVERAL PROBLEMS REVOLVING AROUND CIGS AND
VSBY'S. VSBY'S HAVE DROPPED TO VLIFR CONDITIONS IN SOME LOCATIONS
BEHIND THE WARM FRONT. DO EXPECT CONDITIONS TO IMPROVE SOMEWHAT
ONCE THE COLD FRONT PASSES THROUGH MHK BY 21Z AND TOP/FOE BY 23Z.
NEXT CONCERN IS WHEN THE PRECIP WILL CHANGE OVER TO FREEZING OR
FROZEN. NAM AND GFS MODELS DIFFER IN TIMING WITH GFS MUCH LATER.
DECIDED TO BLEND AND PLACED PL IN THE TAFS AFT 10Z AT MHK AND 15Z
AT TOP/FOE AS SFC TEMPS FALL BELOW FREEZING. LEANING MORE TOWARD
PL AS FORECASTED COLUMN INDICATES BELOW FREEZING TEMPS FROM SFC TO
3K FT.
BYRNE
&&
.TOP WATCHES/WARNINGS/ADVISORIES...WINTER STORM WARNING FROM MIDNIGHT
THURSDAY TO 6 PM FRIDAY FOR KSZ008-KSZ009-KSZ020-KSZ021-KSZ034-KSZ035.
WINTER STORM WARNING FROM 6 AM THURSDAY TO 6 PM FRIDAY FOR
KSZ010-KSZ011-KSZ012-KSZ022-KSZ023-KSZ024-KSZ036-KSZ037-KSZ038-
KSZ054.
WINTER STORM WARNING FROM NOON THURSDAY TO 6 PM FRIDAY FOR
KSZ026-KSZ039-KSZ040-KSZ055-KSZ056-KSZ058-KSZ059.
&&
$$
