FXUS63 KEAX 051119
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
519 AM CST SAT DEC 5 2009
...UPDATED AVIATION DISCUSSION...
.DISCUSSION...
PRIMARY FOCUS IS ON THE STORM SYSTEM PROGGED TO MOVE ACROSS THE
PLAINS INTO THE UPPER MIDWEST ON SUNDAY. PRIOR TO THAT...THE SURFACE
HIGH TO THE EAST WILL CONTINUE TO SLOWLY MOVE EAST AND LEE SIDE LOW
PRESSURE WILL STRENGTHEN UNDER NEARLY ZONAL FLOW. COLD
CANADIAN/ARCTIC HIGH PRESSURE WILL BE SLIDING SOUTH DOWN THE PLAINS.
THESE TWO AIRMASSES WILL BE UNDERGOING A SQUEEZE PLAY...FORCING A
FRONTAL BOUNDARY TO DEVELOP. MODELS HAVE STARTED TO COME INTO
AGREEMENT SHOWING THE BOUNDARY SETTING UP FROM SOUTH CENTRAL KANSAS
NORTHEASTWARD ACROSS NORTHWEST MISSOURI INTO NORTHEAST IOWA.
MODELS HAVE ALSO BEEN FAIRLY CONSISTENT SHOWING THE SHORTWAVE...
CURRENTLY OVER THE PACIFIC NORTHWEST...DROPPING INTO THE SOUTHWEST
U.S. BEFORE QUICKLY MOVING EAST ACROSS THE REGION BY SUNDAY NIGHT.
ISENTROPIC UPGLIDE OVER THE DEVELOPING SURFACE BOUNDARY AHEAD OF THE
SHORTWAVE WILL AID IN THE DEVELOPMENT OF PRECIP. QUESTIONS REMAIN
WITH THE TEMPERATURE PROFILE AS WELL AS HOW MUCH MOISTURE WILL BE
AVAILABLE. FORECAST SOUNDINGS SUGGEST DEEP ENOUGH MOISTURE FOR ALL
SNOW. DUE TO THE BRIEF NATURE OF THE EVENT...SNOW AMOUNTS WILL MOST
LIKELY BE AROUND ONE INCH ACROSS NORTHWEST INTO NORTH CENTRAL
MISSOURI.
PRECIP AHEAD OF THE BOUNDARY WILL BE A LITTLE TRICKIER. DRY AIR
ABOVE 700-800MB SHOULD EFFECTIVELY ELIMINATE ICE CRYSTAL GROWTH IN
THE DENDRITIC LAYER THEREBY PREVENTING SNOW. DO EXPECT A CLOUD LAYER
ABOVE THE DRY AIR...SO NEXT QUESTION IS WILL THE DRY LAYER BE TOO
MUCH FOR FEEDER-SEEDERS. CONTINUED TO FORECAST DRIZZLE FOR SUNDAY
AFTERNOON. REINTRODUCED LIGHT SNOW AND FREEZING DRIZZLE SUNDAY NIGHT
WITH LOW CLOUD LAYER AND CYCLONIC FLOW CONTINUING. SYSTEM WILL HAVE
MOVED WELL EAST...LEAVING COLD AND DRY CONDITIONS FOR MONDAY.
33
MEDIUM RANGE (TUE-THU)...
/435 PM CST FRI DEC 4 2009/
THE BIG WEATHER MAKER FOR NEXT WEEK REMAINS ON TRACK FOR AN ARRIVAL
IN THE TUE TO WED TIMEFRAME. WHILE THERE IS HIGH CONFIDENCE THAT
PRECIP WILL BE RECEIVED IN THE CWA...MUCH LIKE TYPICAL WINTER STORMS
IN MISSOURI AND KANSAS...STORM TRACK...STORM INTENSITY...AND PRECIP
TYPE REMAIN HIGHLY IN QUESTION. NEVERTHELESS...PRECIP CHANCES HAVE
BEEN SIGNIFICANTLY INCREASED.
THIS BEING SAID...MED RANGE GUIDANCE CONTINUES TO WAFFLE A BIT IN
REGARDS TO THE MOST IMPORTANT DETAILS OF THE FCST. MUCH OF THIS IS
DUE TO THE POOR SAMPLING OF UPR LVL DYNAMICS ASSOCIATED WITH THIS
WAVE JUST NOW ROTATING ACROSS THE WESTERN CANADIAN COASTLINE. OF
MORE CONCERN ON MODEL EVOLUTION OF THIS SYSTEM IS THE INTENSITY OF
THE HIGHLY AMPLIFIED RIDGE OFF THE PAC NW ALONG WITH THE JET
DYNAMICS ASSOCIATED BETWEEN THESE SYSTEMS.
WHILE THE 12Z GFS WAS A BIT OF AN OUTLIER...WE'RE ALSO BEGINNING TO
SEE SOME DISTINCT SIGNALS FROM THE 06Z/12Z ENSEMBLE MEMBERS AS WELL
AS THE NAEFS SUPER ENSEMBLE SUPPORTING THE DEVELOPMENT OF A MUCH
STRONGER SFC AND LOW LVL CIRCULATION BY TUESDAY AFTN AS SUGGESTED BY
BOTH THE GEM/ECWMF/GFS IN PREVIOUS RUNS. BOTH THE U AND V
COMPONENTS (ESPECIALLY THE U COMPONENT) OF THE 850MB WINDS ARE MUCH
MORE ANOMALOUS THIS MORNING...SUGGESTING A MUCH STRONGER COLD
CONVEYOR BELT AND DEEPER INFLUX OF WARM AND RICH THETA E AIR FROM
THE SOUTHWEST. THIS MAY ONLY FURTHER INCREASE THE BAROCLINICITY OF
THIS SYSTEM AND COULD RESULT IN EVEN SLOWER...FURTHER SOUTH...AND
POTENTIALLY MORE INTENSE SOLNS IN THE SHORT TERM DESPITE THE
PROGRESSIVE NATURE OF THE EVENT. THE 06Z/12Z GEFS CONFIDENCE MAPS
CONTINUE TO SHOW AND ABOVE NORMAL CONFIDENCE LEVEL IN BRINGING
FREEZING TO ABOVE FREEZING TEMPERATURES WELL INTO NORTHERN MISSOURI
TUE AFTN...GIVEN CONSISTENT CLUSTERING AND STRONGER LOW-LVL
FEATURES. NAEFS MEANS ALSO SUGGEST 850MB TEMPS CLIMBING ABOVE 0 BY
18Z TUE FROM A KMCI TO KIRK LINE SIMILAR TO THE OPERATIONAL 12Z
GFS/00Z ECMWF. ALL IN ALL...THIS IDEA WOULD SUPPORT A MUCH HIGHER
PROBABILITY THAT EITHER MIXED PRECIP OR RA/SN WOULD CREEP MUCH
FURTHER NORTH TUE AFTN THAN WHAT PREVIOUS OPERATIONAL MODELS HAVE
SUGGESTED AND THE OVERALL BAROCLINICITY OF THE LOWER-LVLS WILL BE
HIGHER THAN SUGGESTED. FOR NOW...WILL BUMP UP MAX TEMPS IN THE
SOUTHERN CWA AND INTRODUCE RA/SN UP TO I-70 TUE AFTN.
THIS BEING SAID...WE'RE STILL OVER 4 DAYS OUT ON THIS STORM...WITH
MANY VARIABLES TO BE IRONED OUT. HOWEVER...ALL INDICATIONS POINT TO
THIS SYSTEM HAVING A HIGH PROBABILITY OF PRODUCING WHAT COULD BE
SIGNIFICANT IMPACTS TO A PORTION OF THE MID-LOWER MISSOURI RIVER
VALLEY. FROM A PROBABILITY STANDPOINT FROM CURRENT
DATA...INDICATIONS POINT TO THE HIGHEST PROBABILITY OF HEAVY SNOW TO
FALL IN NORTHERN KANSAS AND NORTHERN MO. WITH PROBABILITIES
DECREASING FURTHER SOUTH INTO CENTRAL/SOUTHERN MO DUE TO THE PENDING
UNCERTAINTY IN THE INFLUX OF WARM AIR ALOFT. THERE WILL LIKELY BE A
SHARP CUTOFF TO SNOWFALL FOR THIS SYSTEM.
BEHIND THIS SYSTEM...GROWING CONFIDENCE IN A TEMPORARY INTRUSION OF
VERY COLD TO PERHAPS ARCTIC AIR (GIVEN POTENTIAL CROSS POLAR FLOW
SETUP AND SHIFTING OF POLAR LOW FURTHER SW). WITH A GOOD LIKELIHOOD
OF SNOW COVER IN NORTHERN MO BY WED NIGHT INTO THUR MORNING HAVE
DROPPED LOWS TO SINGLE DIGIT READINGS. WINDS WILL ALSO BE A MAJOR
CONCERN ON WEDNESDAY GIVEN THE EXPECTED DEEPER CYCLOGENESIS AT THE
SFC.
DUX
&&
.AVIATION...
VFR CONDITIONS EXPECTED THROUGH THE TAF FORECAST PERIOD. MAIN CONCERN
WILL BE WITH WINDS BY LATE THIS MORNING AND INTO THIS AFTERNOON AS
LLVL PRESSURE GRADIENT TIGHTENS ALLOWING SFC FLOW TO INCREASE AND 20-30KT
LLJ TO DEVELOP OVERHEAD. AS LAPSE RATES STEEPEN DURING THE
DAY...DOWNWARD MOMENTUM TRANSFER SHOULD ALLOW GUSTY CONDITIONS TO
DEVELOP AND CONTINUE UNTIL THE LATE AFTERNOON HOURS. OTHERWISE...HIGH
LEVEL CLOUDINESS WILL BE ON THE INCREASE BY THIS EVENING AND TONIGHT.
DEROCHE
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&
$$
