FXUS63 KEAX 221810
AFDEAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
1209 PM CST TUE DEC 22 2009

...UPDATED AVIATION DISCUSSION...

.DISCUSSION...
/455 AM CST MON DEC 21 2009/
ELONGATED PV ANOMALY (OR STRING OF PV ANOMALIES) DIVING SOUTH ALONG 
THE PACIFIC NORTHWEST COAST TOWARDS A WEAKNESS IN THE HEIGHT FIELD 
ACROSS THE DESERT SOUTHWEST WILL BECOME THE MAIN PLAYER IN STRONG 
CNTRL CONUS CYCLOGENIC EVENT THIS WEEK. OF MORE IMMEDIATE CONCERN IS 
A WEAK FRONTAL BOUNDARY AND DENSITY CURRENT SURGE THROUGH CNTRL 
NEBRASKA WORKING TOWARDS THE CWA THIS MORNING. NAM-WRF SEEMED TO 
CAPTURE THIS SHALLOW BOUNDARY MOST ACCURATELY...ESSENTIALLY WASHING 
THE BOUNDARY INTO A QUASI-STATIONARY WARM FRONT THIS AFTERNOON...AS 
LOW LEVEL MOISTURE CONVERGES FROM ALL DIRECTIONS. DIFFICULT 
TEMPERATURE FORECAST FOR THE NEXT 24 HOURS...AS UPPER 40S AND LOWER 
50S NOT THAT FAR AWAY ALONG THE I-40 CORRIDOR ATTEMPT TO WORK 
NORTH...YET BOUNDARY LAYER MAINTAINS AN ELY FETCH...AND INCREASING 
CLOUD COVER HELPS MUTE ANY ADDED DIURNAL EFFECTS. 
CORRESPONDINGLY...WITH ADDED CLOUD COVER AND GRADIENT ELY WINDS 
RESPONDING TO LEE SFC CYCLOGENESIS IN THE SRN HIGH PLAINS...FAIL TO 
SEE HOW OVERNIGHT LOWS WOULD DROP MUCH AT ALL (AND EVEN POSSIBLY 
RISE WITH A SURGE OF HIGHER THETA-E AIR OVERNIGHT). 

MODELS HAVE DEFINITELY TRENDED TOWARDS THE PREVIOUSLY PREFERRED 
ECMWF TYPE SOLUTION...BRINGING THE MAIN COLD CORE CIRCULATION CENTER 
FROM NEW MEXICO THROUGH CNTRL KANSAS...AND TOWARDS FAR NWRN MISSOURI 
BY THURSDAY EVENING (OPERATIONAL GFS STILL REMAINS ON THE ERN 
PERIPHERY OF ALL GUIDANCE...WITH THE NAM-WRF TOWARDS A MORE WRN 
EXTREME). IT SHOULD BE STATED THAT ON A GLOBAL SYNOPTIC SCALE WITH 
CURRENT MODEL RESOLUTION AS IT IS...THIS TYPE OF SPREAD IS ACTUALLY 
QUITE REASONABLE...THE PROBLEM BEING SO MUCH OF THE SENSIBLE WEATHER 
IS DRIVEN ON THE SUB-SYNOPTIC SCALE...AND ONLY SMALL PERTURBATIONS 
IN THE INITIALIZATION FIELDS CAN CAUSE A SHIFT OF ONLY A FEW GRID 
POINTS...AND THUS COMPLETELY AFFECTING THE FORECAST PROCESS AND 
IMPACT PERSPECTIVE (CONVERSELY THINK OF IT IN THE OPPOSITE 
PERSPECTIVE...IF THE SPREAD OF A FORECAST RIDGE OF HIGH PRESSURE HAD 
THIS TYPE OF UNCERTAINTY...THE IMPACT BASE WOULD BE QUITE 
NEGLIGIBLE). 

REGARDLESS...IT IS ALSO BECOMING APPARENT THAT SEVERAL SHORTWAVES 
EMANATING FROM THE MAIN HEIGHT ANOMALY CENTER WILL PROPAGATE THROUGH 
THE REGION PRIOR TO A REINFORCING WAVE FROM THE NRN STREAM PV 
RESERVOIR CONSOLIDATING INTO A BAROTROPICALLY STACKED CIRCULATION 
OVER NRN MISSOURI BY FRIDAY MORNING. THIS IS A TYPICAL PROCESS FOR 
WAVES EJECTING ACROSS THE SRN ROCKIES...AND WILL BE MANIFESTED BY 
SEVERAL INSTANCES OF ISENTROPICALLY INDUCED LIFT THROUGH THE AREA 
OFFSET BY SINKING MOTION WITH THE PASSAGE OF EACH SHORTWAVE. GRADUAL 
WEAK LIFT WILL BEGIN LATER THIS AFTERNOON...THOUGH WITHIN A 
RELATIVELY SHALLOW LAYER...LIKELY ONLY RESULTING IN SOME DRIZZLE AND 
SPRINKLES. NRN TIER OF COUNTIES MAY BE FLIRTING RIGHT AROUND THE 
FREEZING MARK..AND AT THIS TIME THINKING ANY VERY LIGHT PRECIP WOULD 
HAVE LITTLE IMPACT...ONLY PARTIALLY FREEZING ON WELL EXPOSED 
SURFACES (IE. TREES AND CARS ETC). SIMILAR THINKING ALSO APPLIES FOR 
TONIGHT WITH LITTLE CHANGE IN TEMPERATURE EVEN AFTER DARK...AND HAVE 
OPTED TO NOT ISSUE ANY HEADLINES FOR THE TIME BEING.

FAR DEEPER AND MORE ROBUST LIFT WILL COMMENCE LATE TONIGHT AND 
THROUGH WEDNESDAY MORNING...AS THE FIRST SHORTWAVE AND SURGE OF 
HIGHER THETA-E AIR PUSHES NORTH FROM THE SRN PLAINS. MODEL SOUNDINGS 
ALL INDICATE A DECENT MEASURE OF MUCAPE ASSOCIATED WITH A NOSE OF 
SATURATED +4C TO +5C AIR AROUND H8 COINCIDENT WITH MODESTLY STEEP 
MIDLEVEL LAPSE RATES. ANY CONVECTIVE ELEMENT WOULD CERTAINLY LOCALLY 
ENHANCE RAINFALL AMOUNTS EARLY WEDNESDAY MORNING. IT IS VERY 
CONCEIVABLE (AND ALMOST EXPECTED) THAT MUCH OF THE AREA WILL 
EXPERIENCE A BREAK IN PRECIPITATION WEDNESDAY AFTERNOON...AWAITING 
THE ARRIVAL OF THE NEXT PIECE OF ENERGY WEDNESDAY EVENING. 
ANTICIPATE THE ENTIRE CWA WILL BE ABOVE THE FREEZING MARK FROM LATE 
WEDNESDAY MORNING THROUGH EARLY THURSDAY AFTERNOON...WITH THE MOST 
SIGNIFICANT ICING ACROSS THE I-80 CORRIDOR IN IOWA. 

VERY INTENSE DEEPENING AND STRONG MATURING CYCLOGENESIS WILL TAKE 
PLACE THROUGHOUT THE DAY ON THURSDAY...WITH THE OCCLUSION PROCESS 
OCCURRING THURSDAY NIGHT. FIRST CONCERN REGARDING THIS SYSTEM IS THE 
FLOODING POTENTIAL...AS PWATS AOA 2 STANDARD DEVIATIONS ABOVE 
AVERAGE ADVECTING NORTH THROUGH THE WARM SECTOR IN CONCERT WITH DEEP 
LIFT ASSOCIATED WITH A COLLOCATED LLJ AXIS...LEFT FRONT QUADRANT OF 
A IMPINGING JET AXIS...AND NOTABLE VORTICITY ADVECTION/Q-VECTOR 
CONVERGENCE. HINTS OF ELEVATED INSTABILITY REMAIN ON SOUNDINGS EVEN 
INTO THURSDAY MORNING...SUGGESTING CONVECTIVELY ENHANCED 
PRECIPITATION MAY BE POSSIBLE. HOWEVER...AXIS OF HEAVIEST RAINFALL 
MAY ACTUALLY ALIGN FURTHER TO THE SOUTH AND EAST (CLOSER TO THE I-44 
CORRIDOR)...AS IS TYPICAL WITH MORE PROGRESSIVE SYSTEMS. WILL HOLD 
OFF ON ANY FLOOD WATCH FOR NOW...INSTEAD HIGHLIGHTING THE POTENTIAL 
IN AN ESF AND HWO PRODUCT.

SECOND CONCERN IS THE POTENTIAL FOR WINTER PRECIPITATION AS THE COLD 
CORE ALOFT PROGRESSES OVER THE AREA...AND DEEP COLUMN COOLING OCCURS 
WITHIN A SATURATED ENVIRONMENT. OF NOTE FROM A CLIMATOLOGICAL 
STANDPOINT...OVERALL HEIGHT ANOMALIES ARE IN THE 2-3 NORMALIZED 
STANDARD DEVIATION RANGE (SIGNIFICANT BUT NOT OVERWHELMING)...WITH 
OVERALL TEMPERATURES AND THICKNESSES HARDLY ANOMALOUS. THE MOST 
SIGNIFICANT PORTION OF THIS SYSTEM IS THE DEEP SLP AND LOW LEVEL 
WIND ANOMALIES...WITH PRESSURE ANOMALIES PEAKING IN THE 3-4 SD BELOW 
AVERAGE RANGE...AND H8-H9 WIND ANOMALIES GREATER THAN 4 SD AWAY FROM 
AVERAGE (AND ESPECIALLY FOR THE ELY WINDS NORTH OF THE WARM FRONT IN 
IOWA FEEDING THE INTENSE TROWAL FORMATION TOWARD THE INVERTED TROUGH 
STRUCTURE THROUGH CNTRL/ERN NEBRASKA). ASIDE FROM THE ICE/SLEET 
PROBLEM ACROSS IOWA...THE KEY TO THE INTENSE SNOWFALL APPEARS TO BE 
THE LOCATION AND STRUCTURE OF THIS INVERTED TROUGH AND DIRECT 
CIRCULATION WITH THE INFLUX OF WARMER MOIST AIR ON THE ANOMALOUS 
ELEVATED WARM CONVEYOR BELT. BEST COMBINATION OF ALL PARAMETERS 
LOOKS TO BE FROM CNTRL KANSAS THROUGH CNTRL/ERN NEBRASKA/SWRN 
MINNESOTA...WITH THE DISTINCT POSSIBILITY OF LOCALLY UP TO 20 INCHES 
OF ACCUMULATION THERE. ANALYSIS OF CIPS ANALOG CASES REVEALS SEVERAL 
GOOD CASES WITH BOTH SIMILAR UPPER LEVEL FEATURES AND SFC 
TEMPERATURES (FEB 28 1987...FEB 24 2007...AND MAR 27 1983)...ALL OF 
WHICH ARGUE FOR THIS CNTRL PLAINS TO UPPER MIDWEST CORRIDOR. 
THINKING THE FAR NW CORNER OF MISSOURI STANDS THE BEST CHANCE OF 
EXPERIENCING MORE SIGNIFICANT SNOWFALL.

OUTSIDE OF THIS AREA...MOST OTHER LOCATIONS MAY ACTUALLY SEE THE 
MOST SNOW ON FRIDAY...AS A DRY SLOT MAY CUT OFF ICE NUCLEATION 
THURSDAY NIGHT...BEFORE THE PV ANOMALY BECOMES RECHARGED AND 
RECIRCULATED ABOUT THE PARENT LOW OVER NRN MISSOURI. MODELS ARE 
ACTUALLY IN VERY GOOD AGREEMENT WITH THIS SCENARIO...DEPICTING A 
GENERAL 1-2 INCH SNOWFALL FOR JUST ABOUT ALL LOCATION NORTH OF THE 
MISSOURI RIVER FRIDAY. INCREASED POPS DURING THIS TIME PERIOD...BUT 
ALSO KEPT TEMPERATURES FROM FALLING TOO QUICKLY GIVEN CLOUD COVER 
AND THE STILL INFLUENTIAL BAROTROPIC NATURE TO THE MIDLEVEL 
CIRCULATION. ALL TOLD...MAY EVENTUALLY NEED SOME SORT OF HEADLINES 
FOR THE NRN HALF OF THE CWA (AND IN PARTICULAR THE NWRN CWA) 
THURSDAY NIGHT THROUGH FRIDAY.

21

&&

.AVIATION...

WARM FRONT CONTINUES TO SHARPEN THIS AFTERNOON...WITH THE AREA 
/STILL/ IN THE CLEAR BETWEEN TWO ADVANCING AREAS OF STRATUS FROM THE 
NORTH AND SOUTH. RAPID NORTHWARD MOISTURE ADVECTION SHOULD HELP 
TRANSPORT THE WARM SECTOR STRATUS INTO THE KANSAS CITY TERMINALS BY 
MID AFTERNOON WITH LOWER END MVFR CEILINGS PREVAILING AFTER 21Z. THE 
NORTHERN STRATUS DECK HAS REMAINED QUASI-STATIONARY THROUGH THE 
MORNING...BUT SHOULD BEGIN TO PUSH SOUTHWARD TOWARD THE SURFACE 
BAROCLINIC ZONE AS THE LOW LEVEL DENSITY GRADIENT SLOSHES SOUTHWARD. 
THIS SHOULD PUT STJ...PRESENTLY NORTH OF THE BOUNDARY...IN LOWER END 
IFR STRATUS BY LATE AFTERNOON.

WITH TIME...CEILINGS WILL BEGIN TO CRASH ON BOTH SIDES OF THE FRONT 
AS COPIOUS LOW LEVEL MOISTURE CONTINUES TO STREAM NORTH AHEAD OF THE 
DEVELOPING WESTERN STORM. INITIALLY...CLOUDS SHOULD BE CONFINED TO 
THE BOUNDARY LAYER...YIELDING AREAS OF DRIZZLE BY MID-LATE 
EVENING...WITH BROADER SYNOPTIC LIFT AND DEEPER MOISTURE LEADING TO 
AREAS OF STEADIER PRECIPITATION IN THE FORM OF SHOWERS BY WEDNESDAY 
MORNING.

WINDS WILL BE LGT/VRB IN THE VICINITY OF THE WARM FRONT THIS 
AFTERNOON...BUT SHOULD TREND EAST TO NORTHEAST OVERNIGHT AS THE WARM 
FRONT BEGINS TO RESTRUCTURE. CEILINGS/VISIBILITIES WILL BE SOLIDLY 
IN THE IFR RANGE AFTER 06Z AND MAY TEMPORARILY LOWER TO LIFR WITHIN 
PRECIPITATION TOWARD DAYBREAK.

BOOKBINDER

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&

$$