FXUS63 KTOP 061752
AFDTOP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1152 AM CST SUN DEC 6 2009
.UPDATE...
UPDATED FOR 18Z TAFS
&&
.DISCUSSION...
SEE PREVIOUS DISCUSSION
&&
.AVIATION...
MAIN TAF CONCERN IS WHEN -DZ/-FZDZ IS EXPECTED TO BEGIN AND CIGS.
CONDITIONS REMAIN VFR ACROSS THE TAF SITES AT ISSUANCE TIME...BUT
EXPECT CONDITIONS TO BECOME MVFR BY 22Z AS SFC FRONT PUSHES EAST.
500MB WAVE EXPECTED TO MOVE THROUGH KS AND DRAG SFC LOW NORTHEAST
OF TAF SITES BY 05Z. PRECIP WINDOW WILL OCCUR BETWEEN 00Z-
05Z. TOUGH PART IS DETERMINING IF PRECIP WILL BE LIQUID OR
FREEZING. EXPECT BELOW FREEZING SFC TEMPS TO SWEEP IN BEHIND FRONT
WHICH SHOULD PASS THROUGH TOP/FOE BY 00Z AHEAD OF PRECIP...BUT IF
AFTERNOON SURFACE TEMPS REACH EXPECTED HIGHS...MAY SAY PRECIP FALL
INITIALLY AS LIQUID AND BECOME FREEZING AS COLDER SFC AIR MOVES
IN. CURRENTLY EXPECTING CIGS TO NOT FALL BELOW MVFR...BUT MAY SEE SOME
VARIABLE IFR CONDITIONS LATER TONIGHT.
BYRNE
&&
.PREV DISCUSSION... /ISSUED 533 AM CST SUN DEC 6 2009/
UPDATE...
UPDATED TO INCLUDE THE 12Z AVIATION DISCUSSION.
AVIATION...
FOR THE 12Z TAFS...VFR CONDITIONS WILL START THE FORECAST PERIOD.
CIGS WILL BEGIN TO DEGRADE THIS AFTERNOON WITH INCREASING
ISENTROPIC ASCENT AND MOISTURE TRANSPORT AHEAD OF UPPER LEVEL
SYSTEM MOVING THROUGH THE NW CONUS. COLUMN SATURATES ENOUGH TO
PRECIPITATE AFTER 22Z. FORECAST MODEL SOUNDINGS INDICATE MID
LEVEL TEMPS AOA -10C...UNFAVORABLE FOR ICE CRYSTALS. COOLER TEMPS
AT MHK MAY ALLOW FOR SNOW TO MIX IN...SO INTRODUCED -DZSN. SFC
TEMPS DROPPING BELOW 32F WILL ALLOW FOR DRIZZLE FURTHER WEST AT
TOP/FOE TO FREEZE. PRECIP SHOULD END AFTER 05Z...BUT MVFR
CONDITIONS WILL PERSIST.
LUNDE
PREV DISCUSSION... /ISSUED 336 AM CST SUN DEC 6 2009/
DISCUSSION...
.MAIN CONCERNS THIS PACKAGE ARE LIGHT MIXED PRECIPITATION TODAY
FOLLOWED BY POTENTIALLY STRONG WINTER STORM ON TUESDAY AND TUESDAY
NIGHT...
PIECE OF ENERGY OVER NC AZ PROGGED TO EJECT OUT INTO THE PLAINS
STATES TODAY...WITH SHORTWAVE TROF AXIS OVER THE FA BY THIS
EVENING. ISENTROPIC LIFT BEGINS TO SATURATE AROUND 285K OUT AHEAD
OF THE WAVE IN THE WESTERN COUNTIES AROUND MID MORNING. WILL HAVE
TWO MAIN CONSIDERATIONS FOR PRECIP TYPE...THE SATURATION OF THE
ICE GROWTH LAYER AND THE SURFACE TEMPS. AT THIS TIME MUCH OF THE
AREA ALONG AND SOUTH OF INTERSTATE 70 REMAINS RELATIVELY DRY IN
THE CRYSTAL GROWTH LAYER WHILE POINTS NORTH SHOULD SATURATE AND
BRING LIGHT SNOW THERE. EAST CENTRAL KS REMAINS ABOVE FREEZING IN
THE AFTERNOON AND WOULD EXPECT DRIZZLE FIRST...FOLLOWED BY A LATE
DAY CHANGEOVER TO LIGHT SNOW AS THE COLUMN SATURATES. NOT
EXPECTING MUCH FOR ACCUMULATION WITH HIGHEST AMOUNTS OF 1-2 INCHES
OF SNOW PAINTED IN NORTH CENTRAL KS WITH NO ACCUMULATION OF SNOW
ALONG AND SOUTH OF THE INTERSTATE. OF NOTE IS AREA ROAD
TEMPERATURES WHICH ARE NEAR FREEZING...SO ANY FREEZING DRIZZLE
THAT DOES MANAGE TO FALL SHOULD FREEZE SHORTLY THEREAFTER. WILL
HAVE TO WATCH THE AREA FROM MANHATTAN TOWARD SALINA AND SOUTH
TOWARD HERINGTON FOR POSSIBLE ACCUMULATIONS AND ADVISORIES IF
NECESSARY TODAY.
MONDAY/TUESDAY...SYSTEM EXITS QUICKLY AND COLD HIGH PRESSURE
MOVES SOUTHWARD BEHIND. HIGHS ON MONDAY IN THE 20S MOST AREAS.
REPRIEVE IS BRIEF AS ISENTROPIC LIFT OVER THE COLD AIR RETURNS BY
0Z TUESDAY. AS WIND SPEEDS INCREASE UP THE SURFACE...COLUMN
SATURATES RATHER QUICKLY. COULD HAVE A BRIEF WINDOW OF A FEW HOURS
WHERE FREEZING DRIZZLE IS POSSIBLE AND WILL BEAR WATCHING. THE
PERIOD OF UPGLIDE IS QUITE PROLONGED...THROUGH 0Z WED ACROSS THE
ENTIRE FA. DEVIL FOR THE SE COUNTIES WILL BE GRADUAL LOW LEVEL
WARMING WITH THE 0C LINE AT 850MB UP TO NEAR I70 BY 0Z HOUR.
MEANWHILE NORTHERN COUNTIES CONTINUE WITH ISENTROPIC LIFT INTO THE
COLD AIR AND FRONTOGENETIC BAND THAT SETS UP OVER THE BORDER
COUNTIES. COUPLED WITH APPROACHING UPPER TROF AND ASSOCIATED LIFT
.WOULD NOT BE SURPRISED TO SEE ACCUMULATION RATES INCREASE IN
THE LATE AFTERNOON HOURS. AND GIVEN CURRENT QPF NUMBERS THAT
COULD BE SEVERAL INCHES. AS TROF AXIS PASSES TUESDAY NIGHT...WRAP
AROUND PRECIP SETS UP AS SFC LOW MOVES EAST OF THE AREA. HAVE KEPT
SNOW AND BLOWING SNOW...AS EXPECT SNOW THAT IS FALLING TO REDUCE
VISIBILITY IN WINDS OF 20-30 MPH. SYSTEM STILL LACKS SOME OF THE
CLASSIC SIGNALS FOR HEAVY SNOW BANDING...BUT SEE ENOUGH OF A
PROLONGED MODERATE SNOW EVENT FOLLOWED BY STRONG NORTHERLY WINDS
THAT BELIEVE A WATCH IS IN ORDER AS THE EVENT COULD HAVE
SIGNIFICANT IMPACT TO TRAVEL FOR NORTHERN ZONES. HAVE HOISTED A
WATCH FOR TUESDAY FOR COUNTIES GENERALLY NORTH OF INTERSTATE 70.
SYSTEM MOVES OUT QUICKLY WITH ANOTHER COLD HIGH MOVING ON BEHIND
ON WEDNESDAY. 67
&&
.TOP WATCHES/WARNINGS/ADVISORIES...WINTER STORM WATCH FROM MIDNIGHT TUESDAY TO 6 AM WEDNESDAY FOR
KSZ008-KSZ009-KSZ010-KSZ011-KSZ012-KSZ020-KSZ021-KSZ022-KSZ023-
KSZ024-KSZ034.
&&
$$
BYRNE
