FXUS63 KEAX 062157
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
356 PM CST SUN DEC 5 2009
.DISCUSSION...
VERY SHORT TERM (TONIGHT THROUGH MON)...
SHORT WAVE MOVING ACROSS KANSAS AT THIS TIME WILL BE ARRIVING AT THE
KANSAS MISSOURI BORDER BY 06Z...AND WILL BE EAST OF THE FORECAST
AREA BY 12Z. RADAR HAS BEEN SHOWING A BAND OF SNOW ACROSS NORTHERN
KANSAS AND SOUTHERN NEBRASKA AHEAD OF THIS WAVE...IN A BAND OF MID
LEVEL LIFT...SHOWING UP BEST AROUND 700 MB. THIS LIFT TRACKS ACROSS
NORTHERN MISSOURI AND SOUTHERN IOWA THIS EVENING...AND ALREADY
GETTING REPORTS OF LIGHT SNOW FALLING IN THE ATCHISON COUNTY
MISSOURI AREA. WILL KEEP CATEGORICAL POPS GOING ACROSS NORTHERN
AREAS TONIGHT...BUT FAST MOVING NATURE OF THIS STORM ALONG WITH
PRECIPITABLE WATER SHOWING .40 OR LESS OF AVAILABLE MOISTURE...NOT
EXPECTING A LOT OF SNOW FROM THIS EVENT. NORTHERN AREAS...FROM ST
JOSEPH TO MACON NORTHWARD MAY RECEIVE AN INCH TO POSSIBLY TWO INCHES
OF SNOW...WITH TEMPERATURES FALLING AS EVAPORATIVE COOLING TAKES
PLACE.
AREAS SOUTH OF HIGHWAY 36 WILL BENEFIT THIS EVENING FROM THE
SOUTHEAST FLOW AHEAD OF THE APPROACHING SURFACE LOW WHICH HAS
BOOSTED TEMPERATURES ABOVE FREEZING...AND UNTIL ANY PRECIPITATION
FORMS...THOSE TEMPERATURES WILL PROBABLY HOLD ABOVE FREEZING EVEN
AFTER SUNSET. SOUNDINGS DO SATURATE THIS EVENING IN THESE AREAS
MAINLY BELOW 800 MB...BUT ARE BORDERLINE FOR ANY ICE CRYSTALS
FORMING TO SUPPORT SNOW...SO WILL KEEP THE IDEA OF DRIZZLE OR
FREEZING DRIZZLE GOING...WITH THE POSSIBILITY OF SOME SNOW MIXING IN
IF THE SATURATION BECOMES DEEP ENOUGH. WICHITA IS REPORTING DRIZZLE
OUT OF THIS DECK...SO THINGS LOOK ON TRACK.
MONDAY WILL BE A BREAK BEFORE THE NEXT STORM MONDAY NIGHT AND
TUESDAY. MODELS SHOWING LOW CLOUDS REMAINING TRAPPED THROUGH THE
MORNING HOURS...WITH ONLY A SLIGHT IMPROVEMENT IN THE CIGS BY
AFTERNOON. WITH NORTH WINDS AND LACK OF SUNSHINE...WILL KEEP DIURNAL
UNDER A 10 DEGREE RANGE.
PC
SHORT TERM (MON NIGHT-WED)...
ABSENT FROM A FEW QUESTIONABLE MODEL RUNS AT 00Z AND 06Z...THE
POTENT WINTER STORM FOR TUE AND WED REMAINS ON TRACK AS SCHEDULED.
ODDLY ENOUGH...THE OFF SYNOPTIC HOURS SIGNIFICANTLY SHIFTED WARMER
LOW-LVL AIR TRAJECTORIES FURTHER NORTH...BECOMING DISTANT OUTLIERS
FROM WELL CLUSTERED ENSEMBLE GUIDANCE. PLEASANTLY...THE LATEST
06Z/12Z NAM HAS TRENDED TOWARDS THE GUIDANCE OF THE 12Z GFS/ECWMF
KEEPING COLDER AIR FURTHER SOUTH AND LIMITING THE NORTHERN EXTENT OF
THE PRECIP TRANSITION ZONE. MAIN FCST CHANGES FOR THIS STORM HAVE
BEEN TO BEGIN FINE TUNING DETAILS IN REGARDS TO PRECIP TYPE AS WELL
AS REFINE PRECIP AMOUNTS.
STILL EXPECTING LARGE SCALE LIFT TO INTENSIFY AFTER 06Z TUE AS
STRONG ISENTROPIC LIFT IS AIDED BY A SLIGHT COUPLED JET STRUCTURE.
THROUGH THE MORNING HOURS EXPECTED PRECIP TO REMAIN AS SNOW...BEFORE
THE INFLUENCES OF WARM AIR ALOFT BEGIN TO NOSE INTO THE AREA. SNOW
ACCUMULATIONS WILL FOCUS IN WESTERN MO...NE KS...AND NW MO.
BY MID-LATE TUE MORNING POINT SOUNDINGS SUGGEST PRECIP BEGINNING TO
TRANSITION FROM S-N AS PRONOUNCED WARM LAYER ARRIVES. LATEST
GUIDANCE IS CONSISTENT IN SETTING UP TRANSITION LINE FROM AROUND
KANSAS CITY TO MOBERLY/KIRKSVILLE. AS FAR AS THE PRECIP TRANSITION
AREA...SOUNDINGS SUGGEST A RATHER UNIFORM WARMUP IN THE LOWER COLUMN
NOT COMPLETELY SUPPORTIVE OF FREEZING RAIN. HOWEVER...DO SEE A SOLN
THAT COULD PLACE A MIXTURE OF SNOW/RAIN/SLEET FOR A SUSTAINED
PERIOD. IN FACT...SOUNDINGS FROM THE NE CORNER OF KC TO THE SE
CORNER OF KC ARE SIGNIFICANTLY DIFFERENT ATTM. FURTHER SOUTH...A
COMPLETE TRANSITION TO RAIN MAY OCCUR AND LINGER IN AREAS FROM
CLINTON TO SEDALIA TO COLUMBIA THROUGH TUE EVE. THIS BEING
SAID...PRECIP WILL COME FAST AND HARD ESPECIALLY IN AREAS OF NE KS
AND NW MO WHERE CROSS SECTIONS SHOW DEEP AND STRONG UVV.
BY THE EVENING...AS TYPICAL IN PROGRESSIVE S/W...STRONG SYNOPTIC
LIFT WILL BEGIN TO REINFORCE THE BAROCLINIC ZONE AIDING IN PRODUCING
ADDITIONAL QPF. MODELS STILL CONTEND THAT A VERY STRONG AND PERHAPS
NARROW BAND OF SNOW WILL BE LIKELY ON THE BACKSIDE OF THIS SYSTEM AS
LOW-LVL FRONTOGENESIS IS MAXIMIZED WITH COLDER AIR SURGE SSE.
GIVEN A POTENTIAL UNSTABLE ATMOSPHERE ALOFT THIS LAST BAND MAY BE
BOTH FAST AND FURIOUS WITH HIGH SNOW RATES. WHILE MUCH OF THE
SOUTHERN HALF OF THE CWA MAY SEE LIMITED SNOWFALL THROUGH THE DAY
(ESP SEDALIA AND BOONVILLE)...THIS BAND SHOULD SWEEP THROUGH AREAS
SOUTH OF KC-MOBERLY AND PROVIDE SNOWFALL ACCUM TO THOSE AREAS
OVERNIGHT. OVERNIGHT TEMPS HAVE ALSO BEEN ADJUSTED UPWARDS GIVEN
THE PROGGED TRACK OF THE SFC LOW. FEEL MUCH OF THE SOUTHERN CWA
WILL REMAIN NEAR OR ABOVE FREEZING.
I STILL HAVE ONE MAJOR CONCERN FOR THIS STORM SYSTEM...AND THAT IS
THE POTENTIAL FOR GUIDANCE TO BE UNDERESTIMATING THE AMOUNT OF COLD
AIR PUSHING SOUTH BEHIND TONIGHTS S/W. 12Z GEFS MSLP SUGGEST THAT
OPERATIONAL MODELS CONTINUE TO BE HAVING A SLIGHT NORTHERN BIAS IN
REGARDS TO THE SFC LOW...WITH 850 MEANS AND ANOMALIES SUGGESTING
COLD AIR MAY STRUGGLE EVEN FURTHER SURGE NWRD. ALSO...ONLY A FEW
GEFS PLUMES IN KS SUGGEST A COMPLETE TRANSITION TO LIQUID. THE 18Z
NAM HAS ALREADY ARRIVED AT THIS CONCLUSION.
OTHERWISE...SIGNIFICANT SNOWFALL AMOUNTS SOME 6-10 INCHES (LOCALLY
HIGHER) WILL BE POSSIBLE ALONG A LINE FROM ATCHISON KS TO KIRKSVILLE
MO. AT THIS JUNCTURE I HAVE UNDERCUT HPC GUIDANCE GIVEN POTENTIAL
FOR LOWER SNOW RATIOS. THROUGH THE DAY TUESDAY THERE MAY BE BE A
SHARP CUTOFF TO WHERE SNOW IS FALLING AND WHERE MIXED PRECIP IS
FALLING AND THIS WILL IMPACT ACCUMULATIONS. THE LAST BAND OF SNOW
TUE NIGHT SHOULD PROVIDE 1-4 INCHES OF SNOW TO THE REMAINDER OF THE
CWFA. ATTM...WILL EXPAND THE WINTER STORM WATCH INTO LEAVENWORTH AND
PLATTE COUNTIES (PRIMARILY NORTHERN AREAS) WHERE PROBABILITIES
SUGGEST THAT NEAR WARNING AMOUNT SNOW MAY FALL. HOWEVER...THERE IS
A DISTINCT POSSIBILITY THAT A SHARP CUTOFF IN SNOW TOTALS COULD
EXIST ACROSS KC AND CENTRAL MO ITSELF WITH UNKNOWN SLEET
ACCUMULATION POTENTIAL ALSO LEADING TO THE POTENTIAL FOR THE WATCH
TO BE EXPANDED ANOTHER TIER OF COUNTIES FURTHER SOUTH.
WEDNESDAY WILL BE BITTERLY COLD AND VERY WINDY. EXPECTING ANY SNOW
WHICH FALLS TO BE BLOWING AROUND AND SIGNIFICANTLY REDUCING
VISIBILITIES IN THE NORTHERN HALF OF THE CWA. OVERNIGHT LOWS
WEDNESDAY NIGHT HAVE BEEN LOWERED NEAR ZERO OVER THE DEEP SNOW PACK.
DUX
EXTENDED (WED NIGHT THROUGH SUN)...
QUITE A BIT OF DISAGREEMENT ON TIMING OF SOUTHERN STREAM SHORT WAVE
HEADING INTO PLAINS AT THE END OF THE WEEK. OPERATIONAL GFS MUCH
FASTER WITH BREAKING OUT PRECIPITATION ACROSS SOUTHERN MISSOURI WITH
THIS WAVE ON FRIDAY...WHEREAS THE ECMWF HOLDS OFF PRECIP UNTIL
FRIDAY NIGHT INTO SATURDAY. WIDESPREAD SOLUTION FROM THE GFS
ENSEMBLES LEADS TO LOW CONFIDENCE ON THIS PART OF THE FORECAST. WILL
KEEP THE SLIGHT CHANCE POPS PREVIOUS FORECAST HAD GOING FOR FRIDAY
NIGHT...WHICH IS A GOOD SPLIT THE DIFFERENCE FORECAST AT THIS
POINT.
OTHER BIG CONCERN FOR THIS PERIOD...WILL BE HOW COLD TO GO WITH
TEMPERATURES BY THURSDAY MORNING AS SURFACE RIDGE BUILD INTO THE
AREA AND A WIDESPREAD SNOWPACK EXPECTED. SOURCE REGION FOR THE
SURFACE AIR MASS WILL BE TAPPING SOME OF THE COLDER AIR SITTING EAST
OF THE CANADIAN ROCKIES...ALTHOUGH THERE WILL BE SOME MODIFICATION
AS IT HEADS SOUTH. MODELS KEEPING TEMPERATURES ABOVE ZERO AT THIS
POINT...BUT WILL HAVE TO WATCH FOR AREAS WHERE WINDS MAY GO CALM BY
12Z THURSDAY IN NORTHEAST KANSAS AND NORTHWEST MISSOURI...WHICH MAY
PRODUCE SOME SUB ZERO READINGS. FOR NOW WILL NOT GO THAT COLD...BUT
SOMETHING THAT CAN BE FINE TUNED ONCE THE SNOW COVER AND TIMING OF
THE SURFACE RIDGE BECOMES CLEARER.
&&
.AVIATION...
/1144 AM CST SUN DEC 5 2009/
FOR THE 18Z TAFS...VFR CIGS EXPECTED TO GRADUALLY LOWER TOWARD THIS
EVENING WITH APPROACHING SHORT WAVE. SURFACE LOW CURRENTLY IN
WESTERN OKLAHOMA WILL SWING INTO EAST CENTRAL KANSAS BY MID EVENING.
AHEAD OF THIS WAVE...SOUTHERLY WINDS WILL KEEP TEMPERATURES ABOVE
FREEZING THROUGH EARLY EVENING. CLOSE CALL FOR THE TAF SITES ON
WHETHER THEY WILL BE SEEING ALL SNOW OR A MIX OF SNOW....DRIZZLE OR
LIGHT RAIN...OR FREEZING DRIZZLE OR LIGHT FREEZING RAIN THIS
EVENING. FOR NOW WILL LEAVE KSTJ AND KMCI ALL SNOW AND KEEP AN EYE
ON UPSTREAM OBSERVATIONS THIS AFTERNOON...BUT WILL HAVE THE
POTENTIAL OF LIGHT FREEZING DRIZZLE MENTIONED IN THE FURTHER SOUTH
KMKC TAF. SURFACE LOW SHOULD PASS THE TAF SITES BY MIDNIGHT SWINGING
THE WINDS AROUND TO THE NORTHWEST. UPPER WAVE SHOULD ALSO BE PASSING
THE TAF SITES AROUND THIS TIME...SO WILL BE ENDING THE
PRECIPITATION...BUT EXPECTING AN IFR TO LIFR DECK OF CLOUDS IN THE
WAKE OF THE SURFACE WAVE. WITH THE FAST MOVING NATURE OF THIS
SYSTEM...WILL START TO IMPROVE CIGS LATE TONIGHT...BUT EXTENSIVE LOW
CLOUD DECK MAY REMAIN TRAPPED FOR MUCH OF THE MORNING...SO WILL ONLY
DO A SLIGHT IMPROVEMENT OF CIGS THROUGH 18Z.
PC
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...WINTER STORM WATCH FROM LATE MONDAY NIGHT THROUGH LATE TUESDAY
NIGHT FOR MOZ001>008-011>017-020>025-028.
KS...WINTER STORM WATCH FROM LATE MONDAY NIGHT THROUGH LATE TUESDAY
NIGHT FOR KSZ025-102-103.
&&
$$
