000
FXUS63 KMPX 232346
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
546 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.../00Z TAF ISSUANCE/

INVERTED SURFACE TROUGH IS EXTENDING FROM SOUTH TO NORTH ACROSS
WRN MN AND WILL GRADUALLY MOVE EAST THROUGH TUE MORNING...ENDING
UP IN ERN MN BY 18Z TUE BEFORE WEAKENING. ALONG AND TO THE EAST
OF THIS FEATURE WILL CONTINUE SCATTERED TO NUMEROUS SHOWERS
THROUGHOUT MUCH OF THE NIGHT. THESE WILL GENERALLY BE LIGHT...WITH
VISBILITY RESTRICTIONS PRIMARILY CENTERED ON BR/FG/DZ. DEEPEST FOG
AND LOWEST STRATUS IS PRESENTLY ALONG THE BOUNDARY AND THAT WILL
CONTINUE THROUGH THE NIGHT. KMSP SHOULD SEE 1.7 KFT CIGS NOT LONG
AFTER MIDNIGHT. THERE ARE SOME RESIDUAL 1.5 KFT CIGS IN WRN WI TO
THE IMMEDIATE EAST OF KMSP...BUT THINK THEY WILL HOLD IN PLACE
THROUGH MUCH OF THIS EVE. LIFR CONDITIONS LIKELY AT ALL TAF SITES
DURING THE MORNING WITH VERY SLOW IMPROVEMENT TOMORROW DUE TO
LIGHT WIND SPEEDS IN THE LOW LEVELS AND RESIDUAL HIGH MOISTURE.
KMSP LIKELY TO REMAIN AT OR BELOW 1.7 KFT THROUGH THE ENTIRE
MORNING AND POTENTIALLY FOR A BETTER PART OF THE AFTERNOON. SOME
SCATTERING EXPECTED IN WRN MN BY AFTN. WINDS TO BE GENERALLY LIGHT
THROUGH THIS TAF PERIOD AND SHIFT FROM ESE TO NW AS THE TROUGH
PASSES MN AIRPORTS.

&&

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

$$

JLT/MTF