RSS FeedsIssued by NWS Twin Cities, MN
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000 FXUS63 KMPX 240550 AFDMPX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN 1150 PM CST MON NOV 23 2009 .AVIATION... /06Z TAF ISSUANCE/ INVERTED SURFACE TROUGH MEANDERS SOUTH TO NORTH ACROSS WESTERN MN ATTM...JUST TO THE EAST OF KRWF AND KAXN. CEILINGS AND VISIBILITIES CONTINUE TO DETERIORATE AHEAD OF THE TROUGH IN THE VERY WARM AND HUMID AIR MASS. RAIN WILL CONTINUE THROUGH THE NIGHT FROM KMSP ON WEST AND SOUTH ACROSS SOUTHERN MN AS A VIGOROUS STORM SYSTEM PUSHES SLOWLY EAST FROM KANSAS. IFR TO LIFR EXPECTED TO SETTLE IN OVER THE NEXT FEW HOURS FOR KRWF...KMSP...KSTC AND LAST INTO MID MORNING ON TUESDAY BEFORE IMPROVING TO LOW MVFR FOR THE AFTERNOON. PERIODS OF RAIN WILL ACCOMPANY THE LOW CONDITIONS PRIMARILY AT KMSP AND KRWF. KAXN IS ALREADY AT VLIFR IN THE WAKE OF THE TROUGH AND SHOULD BEGIN TO SHOW SOME IMPROVEMENT LATE IN THE NIGHT AS SOMEWHAT DRIER AIR SPREADS IN FROM THE WEST. INDICATIONS ARE FOR KAXN TO SCATTER OUR BETWEEN 18Z AND 21Z ON TUESDAY. KRNH AND KEAU SHOULD SEE IFR CONDITIONS DEVELOP BY MORNING AS THE SURFACE TROF APPROACHES AND PERSIST THROUGH MUCH OF THE DAY. THE TROF WILL THEN PUSH SLOWLY ACROSS WESTERN WI TUESDAY NIGHT. DUE TO THE MOIST LOW LEVEL CONDITIONS AND CYCLONIC FLOW...LOOK FOR CEILINGS AND VISIBILITIES TO LOWER TO IFR AGAIN IN THE EVENING FOR KMSP...KRNH AND KEAU. && .DISCUSSION... /ISSUED 122 PM CST MON NOV 23 2009/ 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.. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...NONE. WI...NONE. && $$ RAH/JLT
