FXUS63 KTOP 080544
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1144 PM CST MON DEC 7 2009

.UPDATE...

UPDATED FOR 06Z AVIATION.

&&

.DISCUSSION...

SEE PREVIOUS DISCUSSION.

&&

.AVIATION...

IFR VISBY/CIGS CURRENTLY EXIST AT ALL TAF SITES AS LIGHT SNOW HAS
OVERSPREAD REGION. ANTICIPATE SNOW TO CONTINUE OVERNIGHT INTO
MORNING WITH MAINLY IFR CONDITIONS CONTINUING. LIFR TO VLIFR IS
EXPECTED BY MID MORNING INTO THE EARLY EVENING AS MODERATE TO
OCCASIONALLY HEAVY SNOW DEVELOPS ACROSS TAF SITES.

BLAIR

&&

PREV DISCUSSION... /ISSUED 339 PM CST MON DEC 7 2009/ 

DISCUSSION...

MAIN CONCERN THIS FORECAST CONTINUES TO BE THE POTENTIAL HEAVY 
SNOWFALL EVENT FOR THE FORECAST AREA.

WATER VAPOR SHOWS UPPER TROUGH DIGGING SOUTHEAST ALONG THE 
CALIFORNIA COAST THIS AFTERNOON WITH WEST SOUTHWEST FLOW OUT INTO 
THE PLAINS. PROFILERS AND WATER VAPOR SHOW MINOR WAVES MOVING OUT OF 
THE ROCKIES AND INTO THE PLAINS THIS AFTERNOON. PERIOD OF PROLONGED 
ISENTROPIC LIFT BEGINS THIS EVENING ACROSS PARTS OF NORTH CENTRAL 
KANSAS THEN SPREADS FURTHER EAST ACROSS THE REST OF THE FORECAST 
AREA OVERNIGHT. ISENTROPIC UPGLIDE OVER COLD DOME WILL PRODUCE LIGHT 
TO MODERATE SNOWFALL TONIGHT THEN ON TUESDAY. MIXING RATIOS OF 3 TO 
4 G/KG ARE FORECAST THROUGH MUCH OF THE PERIOD OF ISENTROPIC LIFT. 
AS THE UPPER SYSTEM MOVES THROUGH THE ROCKIES INCREASING 
FRONTOGENESIS OCCURS ACROSS MUCH OF THE CWA...ESPECIALLY NORTH OF 
INTERSTATE 70. INCREASING DYNAMIC LIFT WITH THE APPROACHING SYSTEM 
AND UPPER DIFFLUENCE ALOFT TUESDAY AFTERNOON WILL LEAD TO MODERATE 
TO HEAVY SNOWFALL TUESDAY AFTERNOON INTO TUESDAY EVENING. CONTINUED 
TO FOLLOW A BLEND OF THE 12Z GFS/00Z AND 12Z ECMWF FOR THIS 
FORECAST. BOTH ARE A LITTLE FURTHER SOUTH WITH THE SURFACE LOW. 
CONCERNED THAT LOW LEVEL COLD AIR WILL NOT RETREAT AS FAR NORTHWEST 
AS EARLIER FORECAST. LATEST FORECAST SOUNDINGS SUGGEST THAT AREA 
FROM LAWRENCE TO JUST NORTH OF EMPORIA WILL SEE A PERIOD OF SNOW AND 
SLEET IN THE AFTERNOON HOURS. FURTHER SOUTHEAST OF INTERSTATE 35 
ENOUGH WARM AIR LOOKS TO MAKE IN THERE TO HAVE A RAIN AND SNOW MIX 
IN THE AFTERNOON. AS THE SURFACE LOW DEEPENS OVER OKLAHOMA TUESDAY 
AFTERNOON THEN RACES NORTHEAST INTO MISSOURI STRONG PRESSURE 
GRADIENT WILL CAUSE WINDS TO INCREASE INTO THE 20 TO 30 MPH RANGE 
WITH GUSTS TO NEAR 36 MPH WHICH WILL CAUSE CONSIDERABLE BLOWING AND 
DRIFTING OF SNOW. ALSO VERY COLD AIR WILL MOVE IN BEHIND THE LOW AND 
WITH THE WINDS PRODUCE WIND CHILLS BELOW ZERO TUESDAY NIGHT. WILL 
ADD COUNTIES TO THE WINTER STORM WARNING FROM LAWRENCE TO EMPORIA 
AND FROM BURLINGTON TO OTTAWA AND GARNETT GO WITH A WINTER WEATHER 
ADVISORY IN THIS AREA. 

53

VERY COLD ARCTIC AIR...NOW OVER SOUTHERN CANADA AND THE NORTHERN 
PLAINS...WILL PLUNGE SOUTHWARD INTO THE CWA THROUGH THE DAY 
WEDNESDAY WITH 850 TEMP FALLING INTO THE -15 TO -17 DEGREE RANGE.
WITH DEEP SNOWCOVER ACROSS AT LEAST THE NORTHERN HALF OF THE 
CWA...WOULD EXPECT TEMPS TO STRUGGLE TO RISE MUCH FROM THE MORNING 
LOWS. HAVE THEREFORE TRIMMED HIGH TEMPS ON WEDNESDAY TO RANGE FROM 
ONLY THE SINGLE DIGITS ACROSS THE NORTH TO THE MID TEENS IN THE FAR 
SOUTHEAST CORNER. WITH GUSTY NORTHWEST WINDS CONTINUING THROUGH THE 
FIRST HALF OF THE DAY...BLOWING SNOW STILL LOOKS TO BE A POSSIBILITY
IN THE NORTHERN 2/3 OF THE CWA ALONG WITH BITTERLY COLD WINDCHILLS.

TEMPERATURES WILL CONTINUE TO BE A CHALLENGE THROUGH THE REMAINDER 
OF THE WEEK WITH SIGNIFICANT SNOWCOVER EXPECTED ACROSS MUCH OF THE 
AREA...LESS CLOUDS AND LIGHTER WINDS...WITH THE COLDEST MORNING
EXPECTED TO OCCUR ON THURSDAY WITH SUBZERO LOWS OVER THE DEEPER
SNOWCOVER IN THE NORTHWEST HALF OF THE CWA. HIGH TEMPERATURES WILL
GRADUALLY MODERATE INTO THE TEENS AND 20S ON THURSDAY...THEN THE
20S AND 30S FRIDAY AND SATURDAY. LOWS WILL RISE INTO THE TEENS ALL
AREAS BY FRIDAY AS ANOTHER SYSTEM MOVES THROUGH THE AREA WITH
ANOTHER ROUND OF WAA BRINGING THE POSSIBILITY OF LIGHT RAIN AND
LIGHT SNOW IN THE SOUTHERN CWA FRIDAY AND FRIDAY NIGHT. ANOTHER
SYSTEM APPROACHES THE CENTRAL PLAINS BY MONDAY WITH ANOTHER CHANCE
FOR LIGHT RAIN OR LIGHT SNOW WITH HIGHS IN THE 30S AND LOWER 40S.

63

&&

.TOP WATCHES/WARNINGS/ADVISORIES...WINTER STORM WARNING UNTIL 6 AM WEDNESDAY FOR KSZ008-KSZ009-
KSZ010-KSZ011-KSZ012-KSZ020-KSZ021-KSZ022-KSZ023-KSZ024-KSZ026-
KSZ034-KSZ035-KSZ036-KSZ037-KSZ038-KSZ039-KSZ040-KSZ054-KSZ055.

WINTER WEATHER ADVISORY UNTIL 6 AM WEDNESDAY FOR KSZ056-KSZ058-
KSZ059.

&&

$$