042 FXUS63 KMPX 170244 AAB AFDMPX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN 944 PM CDT TUE APR 16 2013 .UPDATE... ISSUED AT 929 PM CDT TUE APR 16 2013 THE SPREAD OF OPERATIONAL MODELS AND ENSEMBLE MEMBERS HAS BEEN DECREASING WITH RESPECT TO A BAND OF MDT-HVY SNOW EXPECTED TO DEVELOP FROM SOUTHWEST MN NEWD TO NWRN WI/NERN MN SOMETIME THURSDAY MORNING...CONTINUING THROUGH THURSDAY NIGHT. EVEN THE 00Z NAM WHICH HAS BEEN DEFIANT FOR THE LAST SEVERAL RUNS HAS FINALLY COME INTO LINE WITH ALL OTHER MODELS AND SHOWS THE BAND OF SNOW SIMILARLY PLACED...ALBEIT LIGHTER. THE POSITIONING OF THE RAIN/SNOW LINE IS WHAT IS MOST UNCERTAIN ATTM...WITH THE ECMWF SHOWING JUST ABOUT THE ENTIRE AREA SUPPORTING SNOW THURSDAY MORNING...WHILE THE MORE LIKELY GFS SOLUTION STILL HOLDS ONTO RAIN ACROSS WRN WI AND SERN MN INTO THURSDAY AFTERNOON. THE DEFORMATION BAND COULD BE INTENSE WITH GOOD FRONTOGENESIS AND A CROSS HAIRS SIGNATURE PRESENT FOR MOST OF THE EVENT. NEGATIVE EPV IS ALSO EVIDENT...ESPECIALLY THURSDAY MORNING. CONTINUED THE TREND OF THE DAY SHIFT AND BROADBRUSHED 5 TO 7 INCHES OVER MOST OF THE AREA...BUT THE BEST POTENTIAL FOR 6+ INCHES WILL BE ALONG AND JUST WEST OF A LINE FROM NEW ULM...TO THE TWIN CITIES...TO HAYWARD. FELT CONFIDENCE HAS INCREASED SUFFICIENTLY TO POST A WINTER STORM WATCH THURSDAY INTO FRIDAY MORNING. && .SHORT TERM...(THIS EVENING THROUGH WEDNESDAY) ISSUED AT 1220 PM CDT TUE APR 16 2013 THE MAIN SHORT TERM CONCERN IS WHETHER THE DRIER AIR FROM THE E/NE HOLDS OFF THE PRECIPITATION THRU WED MORNING. CURRENTLY RESIDUAL MOISTURE IN THE LOWEST 1KM WILL SLOWLY ERODE THIS AFTN...WITH PARTLY TO MOSTLY CLOUDY SKIES OVERNIGHT AS MID/HIGHER CLDS BEGIN TO MOVE IN FROM THE SW. DEEP DRY LAYER IS EXPECTED TO MOVE ACROSS THE GREAT LAKES...WHICH WILL HAMPER PRECIPITATION FROM REACHING THE GROUND INITIALLY WED MORNING. IN ADDITION...WET BULB TEMPS ARE COLD ENOUGH DURING THE ONSET OF THE PRECIPITATION TO FORM A MIXTURE OF SNOW/SLEET/RAIN. AFT THE ATMOSPHERE MOISTENS BY MID/LATE MORNING...EXPECT MOST AREAS OF SOUTHERN MN/WC WI TO SEE MAINLY RAIN. THIS WAS THE SCENARIO FROM LAST WEEKENDS STORM WHICH INITIALLY HAD SNOW...THEN RAIN/SNOW...WHICH EVENTUALLY CHG OVER TO ALL RAIN. THE THERMAL PROFILE IS VERY CONDUCIVE FOR A SNOW/RAIN MIXTURE DURING THE MORNING...WITH SNOW ACROSS CENTRAL/WC MN. ANOTHER CHG IN THIS FORECAST PACKAGE IS THE INTRODUCTION OF CONVECTION AND HEAVY RAINFALL POTENTIAL ACROSS SC/SE MN AND PORTIONS OF WC WI. A FLOOD WATCH WILL BE ISSUED LATER TODAY BASED ON CURRENT SOIL CONDITIONS...AND THE ANTICIPATION OF HEAVY CONVECTIVE BANDS. .LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY) ISSUED AT 335 PM CDT TUE APR 16 2013 A POTENTIAL SIGNIFICANT PRECIPITATION EVENT SHOULD HAVE BEGUN ACROSS THE FA BY THE START OF THE LONG TERM. SOLUTIONS VARY WIDELY ON THE TYPE AND AMOUNTS OF PRECIPITATION FROM WEDNESDAY NIGHT THROUGH FRIDAY. WE LIKED THE NAM IDEA ON CONVECTION/HEAVY RAIN POTENTIAL FOR SOUTH CENTRAL MN THROUGH WEST CENTRAL WI WEDNESDAY NIGHT AND EARLY THURSDAY...BUT DISCOUNTED LATER PERIODS OF THE NAM AS IT APPEARS TO NOT HANDLE THE UPPER LOW AND DEFORMATION ACROSS THE UPPER MS VALLEY REGION PROPERLY. PMDHMD INDICATED THE NAM BIAS DUE TO A DEEPER CANADIAN SHORT WAVE AND FASTER MOVEMENT. THE GFS DOES NOT SEEM TO CAPTURE THE CONVECTIVE TREND AND HAS CONSIDERABLY MORE QFP THAN ANY OTHER MODEL WITH REGARDS TO THE UPPER LOW AND DEFORMATION ZONE. THIS IN ITSELF IS TROUBLESOME DUE TO THE POTENTIAL FOR HEAVY SNOW. AS AN EXAMPLE...THE 12Z GFS CARIBOU SNOW TECHNIQUE INDICATES 22 INCHES BY LATE IN THE DAY FRIDAY FOR MSP. THE 06Z RUN WAS OVER A FOOT. A NICE COMPROMISE THAT CAPTURES THE CONVECTIVE/HEAVY RAINFALL POTENTIAL PLUS DEVELOPS THE DEFORMATION SNOW ACROSS WESTERN MN BY THURSDAY EVENING AND SPREADS IT EAST THROUGH FRIDAY WAS THE GEM. THE 12Z EC...WHICH JUST ARRIVED...SUPPORTS THESE IDEAS AS WELL. THEREFORE...A FLOOD WATCH HAS BEEN ISSUED FOR PARTS OF SE MN AND WEST CENTRAL WI FROM 18Z WEDNESDAY TO 18Z THURSDAY. THE NAM PW VALUES CLIMB INTO THE 220-240 PERCENT RANGE ACROSS THESE AREAS. VARIOUS WRF MODELS ALSO SHOW CONVECTIVE ELEMENTS MOVING THROUGH WHICH WOULD LEAD TO HIGH RAINFALL RATES. GENERALLY 1 TO 1.5 INCHES OF RAIN COULD FALL IN THE WATCH AREA. THE 09Z/15Z SREFS CONTINUE TO SHOW PROBABILITIES FOR 2 INCHES OF RAIN IN 24 HOURS IN THE WATCH AREA FROM 15 TO 20 PERCENT. WHILE ALL OF THIS IS GOING ON...THERE WILL BE A TRANSITION TO SNOW HEADING INTO WEST CENTRAL AND CENTRAL MN. AT THIS POINT IT APPEARS THE SNOW AMOUNTS WEDNESDAY NIGHT AND THURSDAY WILL AMOUNT TO 2 TO 4 INCHES. THIS WOULD GENERALLY BE ALONG AND WEST OF A LINE FROM REDWOOD FALLS TO MORA. AN INCH OR TWO OF SNOW EAST OF THIS LINE TO THE WESTERN TWIN CITIES. THE MAIN CONCERN FOR SNOWFALL ACCUMULATION ARRIVES BY THURSDAY EVENING AND LASTS THROUGH FRIDAY AS THE MID LEVEL LOW AND DEFORMATION ZONE WORK NORTHEAST ACROSS THE CWA. CURRENT SNOW RATIOS AND QPF YIELDS SOME 4 TO 7 INCHES OF SNOW ACROSS EAST CENTRAL AND SOUTH CENTRAL MN AND WEST CENTRAL WI WITH ANOTHER 2 TO 4 INCHES TO THE WEST. THE 6 TO 7 INCH AMOUNTS FORECAST FOR THURSDAY NIGHT AND FRIDAY COVER THE THE TWIN CITIES AND AREAS TO THE NORTHEAST. A WINTER STORM WATCH MAY BE NEEDED SOON IF THIS TREND HOLDS. A BRIEF DRY PERIOD IS EXPECTED FRIDAY NIGHT AND SATURDAY BEFORE MORE MIXED PRECIPITATION ARRIVES FOR SATURDAY NIGHT AND SUNDAY. THIS PRECIPITATION EVENT MAY BE ANOTHER LONG DURATION ONE DUE TO NORTHERN AND SOUTHERN STREAM ENERGY INTERACTION. THIS MAY KEEP PRECIPITATION IN OUR AREA THROUGH TUESDAY WITH HEAVY RAIN POTENTIAL FOR SE MN AND PARTS OF WEST CENTRAL WI ONCE AGAIN. NEEDLESS TO SAY...TEMPERATURES WILL BE BELOW NORMAL THROUGH THE NEXT 7 DAYS. HOWEVER...THERE DOES SEEM TO BE SOME LIGHT AT THE END OF THE TUNNEL AS A MASSIVE UPPER RIDGE ON BOTH THE GFS AND EC MOVES INTO THE NORTHERN PLAINS LATE NEXT WEEK. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING) ISSUED AT 542 PM CDT TUE APR 16 2013 MVFR CIGS HAVE ERODED NORTH DURING THE AFTERNOON. WILL BRING IN LOWERING MID LAYER DECK AND EVENTUALLY MVFR OVER THE WEST TOWARD 12Z. WILL SPREAD THAT EAST INTO WEST CENTRAL WI IN THE AFTERNOON. IFR DEVELOPING OVER MN PORTION IN THE AFTERNOON. ANOTHER CONCERN WILL BE PCPN TYPE...WITH THE RAIN/SNOW LINE DEVELOPING NORTH AND WEST OF THE METRO INTO THE MORNING. WILL CARRY JUST SNOW AT KAXN/KSTC WITH RASN AT KRWF INTO THE AFTERNOON. REMAINDER OF THE AREA SHOULD REMAIN JUST RAIN. SOME THREAT OF THUNDER AS WELL...WITH THE GREATER THREAT DEVELOPING MAINLY EAST OF THE METRO INTO SOUTHEAST MN AND PERHAPS TRAILING NORTH TOWARD KEAU BY LATE AFTERNOON/EVENING. SHOULD REMAIN ISOLD...SO WILL LEAVE OUT FOR NOW. LIGHT NORTH/NORTHEAST WINDS THIS EVENING BECOMING MORE EAST INTO WEDNESDAY AS SURFACE LOW DEVELOPS AND MOVES OUT INTO THE CENTRAL PLAINS. KMSP... LOWER CLOUDS CLEARING TO THE NORTH BY SUNSET...WITH SOME MID CLOUDS MOVING IN RAPIDLY OVERNIGHT. LOWERING CIGS TO MVFR BY LATE MORNING WITH -RA DEVELOPING AFTER 16Z OR SO. MAY SEE A BRIEF MIX RASN ON THE ONSET...BUT WILL REMAIN PREDOMINANTLY RAIN INTO WED NIGHT. IFR GIGS MAY DEVELOP LATER INT THE AFTERNOON AS THE HEAVIER PRECIPITATION/SATURATION OCCURS. LIGHT NORTH/NORTHEAST WIND INTO TH NIGHT BECOMING MORE EAST WEDNESDAY AHEAD OF DEVELOPING SURFACE LOW OVER THE CENTRAL/SOUTHERN PLAINS. /OUTLOOK FOR KMSP/ WED NIGHT...MVFR/IFR CIGS/VSBYS IN RA. NE WIND...BCMG N 10 TO 20 KTS. THU...IFR WITH -RA BECOMING SN. NW WIND 15-20 G25 KTS. FRI...MVFR/IFR WITH SN LIKELY. NNW WIND 20 G30 KTS. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...WINTER STORM WATCH FROM THURSDAY MORNING THROUGH FRIDAY MORNING FOR MNZ043>045-049>053-056>070-073>078-082>085-091-092. FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY AFTERNOON FOR MNZ077-078-085-093. WI...WINTER STORM WATCH FROM THURSDAY MORNING THROUGH FRIDAY MORNING FOR WIZ014>016-023>025. FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY AFTERNOON FOR WIZ015-016-023>028. && $$ UPDATE...BORGHOFF SHORT TERM...JLT LONG TERM...RAH AVIATION...DWE