000
FXUS63 KMPX 232149 CCA
AFDMPX

AREA FORECAST DISCUSSION...CORRECTION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
122 PM CST MON NOV 23 2009

.DISCUSSION...

VERY ACTIVE WEATHER PATTERN ABOUT TO DEVELOP ACROSS THE UPPER
MIDWEST AS A SERIES OF SHORT WAVES FORCE THE UPPER LEVEL PATTERN
TO BECOME MORE CONDUCIVE OF A PERIOD TO -RA/-DZ...THEN MIXING WITH
AND CHANGING TO -SN BY WED/WED NIGHT.

SHORT TERM CONCERNS DEAL WITH A STRONG UPPER WAVE ACROSS EASTERN
COLORADO THIS AFTN AND HOW THE UPPER LEVEL FORCING BECOMES
ELONGATED AND MOVES E/NE ACROSS IOWA/S MN AND WI. ALTHOUGH THERE
REMAINS SUBTLE DIFFERENCES IN THE OVERALL EVOLUTION OF THIS STRONG
UPPER WAVE...THE MAIN THEME WILL BE A LARGE AREA OF PRECIPITATION
DEVELOPING ACROSS NE/IA...THEN SPREADING E/NE ACROSS SOUTHERN MN
BY LATE THIS EVENING/OVERNIGHT. BY TUESDAY MORNING/AFTN...THE MAIN
INFLUENCE OF THIS SYSTEM WILL BE ASSOCIATED WITH THE MAIN SFC LOW
THAT WILL BE MOVING ACROSS THE IA/MO BORDER BY TUESDAY MORNING...THEN
INTO SOUTHEAST WI BY TUESDAY EVENING. THIS WILL PLACE THE HIGHEST
PERCENTAGES OF WEATHER ELEMENTS ACROSS THE FAR S CWA...BUT STILL 
LIGHT QPF AMTS DUE TO THE SEPARATION OF THE MAIN FORCING TO THE SE 
OF OUR REGION.

AFTER TUE EVENING...THE NEXT SHORT WAVE WILL BE MOVING INTO THE 
NORTHERN PLAINS AND INDUCE A SECONDARY FORCING AREA SOMEWHERE ACROSS 
THE UPPER MIDWEST BY WEDNESDAY AFTN/EVENING. BY LATE WEDNESDAY/THU 
MORNING... A SECONDARY FRONTAL BOUNDARY OR TROUGH WILL MOVE THROUGH 
EASTERN PORTIONS OF THE FORECAST AREA. THE MAIN CONCERNS WILL BE HOW 
COOL THE LOW LEVELS WILL BE AS THE FIRST SYSTEM EXITS...AND WHERE 
THE COLD CORE OF THE NEXT SYSTEM MOVES. THE LATEST GFS REMAINS TOO 
WARM FOR ALL SNOW UNTIL ALL OF THE PRECIPITATION MOVES OUT OF OUR 
REGION. THE NAM/WRF IS MORE OF A COMPROMISE OF THE ENSEMBLE MEANS 
AND IS COOLER AND ALLOWS FOR THE TRANSITION OF RAIN TO SNOW BY 
WEDNESDAY AFTN/EVENING ACROSS MOST OF THE AREA. ALTHOUGH THE GFS 
DOES SHOW SOME CONTINUITY WITH THE OVERALL PLACEMENT OF THE UPPER 
LEVEL SYSTEM ON WED/THU...THE NAM/WRF SEEM TO INDICATE SOME PV 
FORCING (ALONG WITH THE UPPER LOW CLOSE TO OUR CWA) WHICH WILL 
LIKELY INDUCE MESOSCALE COOLING PROCESSES. THEREFORE...RAIN CHANGING 
TO SNOW IS LIKELY WEDNESDAY AFTN IN THE NW...THEN INTO THE SE CWA BY 
LATE WED EVENING. SNOWFALL ACCUMULATIONS WILL BE HIGHLY DEPENDENT ON 
WHEN THE CHANGE OVER OCCURS...AND HOW MUCH LEFT OVER FORCING AND 
MOISTURE REMAINS AS THIS SYSTEM EXITS THURSDAY MORNING. AT THIS 
TIME...HPC SNOWFALL GRIDS SEEM REASONABLE WITH A BROAD AREA OF 1 TO 
3 INCHES ACROSS MOSTLY THE NE 2/3 OF CWA...OR BASICALLY ALONG AND 
NORTH OF AN ALEXANDRIA...TO ST CLOUD TO FBL LINE. HOWEVER...THIS 
HIGHLY DEPENDENT ON THE TRACK OF THE UPPER LEVEL LOW AND IF ANY TYPE 
OF TROWAL SCENARIO DEVELOPS ON THE BACK SIDE OF THIS SYSTEM.

THE EXTENDED OUTLOOK REMAINS VERY PROGRESSIVE WHICH MEANS ANOTHER
WEATHER SYSTEM AFFECTING THE AREA BY SUNDAY. THICKNESS VALUES
REMAIN COLD ENOUGH FOR ALL SNOW AT THIS TIME. ..JLT..

&&

.AVIATION.../18Z TAF ISSUANCE/ 

PCPN SLOLY DMNSHG FAR E MN INTO WC WI AS SHRTWV LIFTS NE THRU AREA. 
EVEN IN PCPN...CIGS HV GNRLY REMAINED VFR. VCNTY INVERTED TROF NR 
MN/DKTS BRDR CONDS RMN IFR...AND WL LIKELY REMAIN SO THRU TAF 
PRD...AFFECTING MAINLY AXN IN THE SHORT TERM. AS TROF MVS EWRD THIS 
EVE/TNGHT IFR CONDS WILL ACCOMPANY IT...WITH IFR CONDS NOT XPCD TO 
REACH MSP TIL AFT 06Z.  WV IMAGERY SHWS SHRTWV ROUNDING BASE OF TROF 
IN COLORADO WITH PCPN EXPANDING ACRS W INTO CNTL NEB.  THIS SURGE OF 
PCPN SHUD SPRED INTO RWF AREA BY 03Z AND MSP AFT 06Z. NOT XPCTG ANY 
CHG TO SNW UNTIL AFT THIS TAF PRD.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&

$$

JLT/BAP