FXUS63 KARX 120253 AFDARX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LA CROSSE WI 853 PM CST THU MAR 11 2010 .UPDATE... FRONT/TROUGH THAT WAS LIFTING NORTH INTO/ACROSS THE FCST AREA HAS STALLED THIS EVENING NEAR A KAUM-KPDC LINE. WINDS ACTUALLY BACKING ACROSS NORTHEAST IA...WITH FRONT LOSING ITS PUSH AND LOOKING TO RETREAT A BIT BACK TO THE SOUTH. DUE TO THIS...MUCH OF SOUTHEAST MN/SOUTHWEST WI WILL REMAIN NORTH OF THIS WARM FRONTAL BOUNDARY TONIGHT...WITH DENSE FOG ONCE AGAIN FORMING NORTH OF IT THIS EVENING AS THE AIRMASS/BOUNDARY LAYER COOL OVER THE COLD/PARTLY SNOW COVERED GROUND. WITH VSBYS ALREADY IN THE LESS THAN 1/4 MILE TO ONE MILE RANGE NORTH OF A KAUM-KPDC LINE AND ALONG/SOUTH OF HWY 10 ACROSS WI...ESPECIALLY OVER RIDGE TOPS AND HIGHER TERRAIN AREAS...HAVE ISSUED A DENSE FOG ADVISORY FOR ALL OF SOUTHEAST MN AND SOUTHWEST INTO CENTRAL WI FOR THE REST OF THE NIGHT THRU MUCH OF FRI MORNING. && .PREV DISCUSSION... /ISSUED 253 PM CST THU MAR 11 2010/ SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT MAIN FORECAST CONCERNS CONTINUE TO DEAL WITH RAIN CHANCES INTO THE WEEKEND. WATER VAPOR/IR IMAGERY THIS AFTERNOON SHOWING CLOSED UPPER LOW/SURFACE LOW OVER CENTRAL IA. 88-D RADAR MOSAIC SHOWS AN EXTENSIVE BAND OF RAIN WITH ISOLATED EMBEDDED THUNDER WRAPPING AHEAD/AROUND THE DEEP 995MB SURFACE LOW ACROSS SOUTHERN WI INTO CENTRAL MN. VIS SATELLITE IMAGERY ALSO SHOWS A CLEARING SLOT EXTENDING FROM EASTERN IA THROUGH IL. THIS HAS ALLOWED FOR MORE HEATING WITH TEMPERATURES PUSHING INTO THE MID 60S TO LOWER 60. COLD FRONT ASSOCIATED WITH THE LOW WAS FIRING A LINE OF AGITATED CU/CB IN THE CLEARING SLOT FROM JUST EAST OF KDBQ TO JUST NORTH OF KSTL ALONG 0-1KM MAX MUCAPE AXIS. LATEST SHORT TERM MODELS LOOK IN PRETTY GOOD AGREEMENT THROUGH THE PERIOD. FOR TONIGHT...COLD FRONT/OCCLUSION PUSHES NORTHWARD THROUGH THE AREA...PUSHING THE MAIN RAIN BAND INTO NORTHERN WI BY MIDNIGHT. WITH THE SURFACE LOW ROTATING FURTHER NORTHEAST INTO THE AREA...WE LOSE THE PRESSURE GRADIENT/WIND. THIS...COMBINED WITH A VERY MOISTURE LADEN BOUNDARY LAYER...EXPECTED TO PRODUCE FOG ONCE AGAIN WITH PATCHY DRIZZLE. NOT AS CONFIDENT ABOUT HOW EXTENSIVE DENSE FOG WILL GET THOUGH. WILL LEAVE TO THE EVENING SHIFT TO MONITOR FOR POSSIBLE HEADLINES. MAIN FORCING ASSOCIATED WITH THE CLOSED UPPER LOW WILL BE NORTHWEST OF THE AREA FRIDAY. THIS LEAVES OUR AREA IN A LULL OF SORTS WITH MAIN RAIN BAND OUT OF THE AREA. NAM DOES SHOW SOME INCREASING LAPSE RATES WITH SOME BREAKS IN THE CLOUD COVER AND COLD CORE LOW ALOFT. LOW LEVEL LAPSE RATES RAMP UP TO AROUND 8C/KM BY AFTERNOON. NAM ALSO BUFKIT INDICATES STRATUS LIFTING INTO A MORE OF A CU/STRATOCU LAYER WITH PERHAPS A ISOLATED -SHRA UNDER THE COLD CORE LOW. WENT WITH MOSTLY CLOUDY SKIES WITH SMALL -SHRA CHANCES. MODELS IN GOOD AGREEMENT IN TAKING THE CORE OF THE CLOSED LOW SOUTH OF THE AREA FRIDAY NIGHT THROUGH SATURDAY WHILE A SECONDARY SURFACE LOW DEVELOPS OVER WESTERN KY AND DUMBBELLS THROUGH SOUTHERN IL INTO EASTERN MO. THIS BRINGS A ANOTHER SURGE OF RAIN NORTH AND WESTWARD INTO THE AREA LATER FRIDAY NIGHT...LASTING THROUGH SATURDAY. MODELS SHOW THE MAIN BAND STAYING SOUTH OF I-90. CORRESPONDINGLY...KEPT LIKELY RAIN CHANCES ACROSS THAT AREA. SMALL RAIN CHANCES WILL LINGER THROUGH SATURDAY NIGHT...MAINLY ACROSS THE SOUTHEAST PART OF THE FORECAST AREA AS THE CLOSED LOW STARTS SHIFT SOUTHEAST INTO THE OHIO RIVER VALLEY REGION. REMOVED RAIN CHANCES OF SUNDAY WITH RIDGING BUILDING INTO THE AREA. LONG TERM...MONDAY THROUGH THURSDAY STILL PRETTY DECENT AGREEMENT BETWEEN THE 11.00Z ECMWF AND 11.06Z GFS THROUGH THE PERIOD. APPEARS EARLY ON //MON INTO MONDAY NIGHT// BOTH MODELS WANT TO DROP A WEAK MID-LEVEL SHORTWAVE TROUGH INTO THE AREA IN NORTHWEST FLOW ALOFT. QPF SEEMS A BIT SKETCHY WITH LOW LEVEL SATURATION IN QUESTION. OPTED TO GO DRY WITH THIS FEATURE FOR NOW BUT INCREASED CLOUD COVER A BIT. WILL HAVE TO KEEP AN EYE ON THIS FOR POSSIBLE INCLUSION OF SMALL PRECIPITATION CHANCES. OTHERWISE... THE REST OF THE PERIOD //TUESDAY THROUGH THURSDAY// LOOKS DRY AND RATHER MILD AS A RIDGE OF HIGH PRESSURE BUILDS INTO THE AREA FROM THE PLAINS. WITH AMPLE SUNSHINE EXPECTED...HIGH TEMPERATURES LOOK LIKE THEY WILL CLIMB WELL INTO THE 50S ACROSS MUCH OF THE AREA. AVIATION...TONIGHT THROUGH FRIDAY MAIN AVIATION CONCERNS ARE LIFR TO IFR CONDITIONS TO CONTINUE AT BOTH TAF SITES TONIGHT INTO FRIDAY. FIRST MAIN RAIN BAND HAS MOVED NORTH OF THE TAF SITES EARLY THIS AFTERNOON. WITH PRESSURE GRADIENT WEAKENING ACROSS THE AREA AND THE COMBINATION OF ABUNDANT LOW LEVEL MOISTURE WILL ALLOW FOR LIFR TO IFR CONDITIONS TO REDEVELOP OVER THE AREA BY 00Z FRIDAY AND CONTINUE INTO FRIDAY MORNING. CONFIDENCE IS LOW AS TO HOW LONG LIFR AND IFR CONDITIONS REMAIN AT BOTH TAF SITES FRIDAY. THE LATEST MODELS CONTINUE TO INDICATE ABUNDANT LOW LEVEL MOISTURE AND A WEAK PRESSURE GRADIENT OVER THE AREA THROUGH THE DAY...AS A SURFACE LOW CONTINUES TO SPIN OVER WESTERN AND SOUTHERN ILLINOIS. FOR NOW...HAVE KEPT PREVIOUS FORECAST TIMING OF LIFR AND IFR CONDITIONS AT BOTH LSE AND RST TAF SITES AFTER 00Z FRIDAY. THOUGH...THE LATEST CONDITIONS OVER SOUTHEAST MINNESOTA INDICATE LIFR CONDITIONS HAVE DEVELOPED WITH VISIBILITIES REDUCED TO A QUARTER OF A MILE. HAVE AMENDED RST TAF FOR THIS. HYDROLOGY... RAIN MELT AND RECENT RAINS HAVE INDEED CAUSED RIVER RISES AND SOME MINOR OVERLAND FLOODING. BULK OF RAIN SHOULD BE PRETTY MUCH DONE BY TONIGHT. ANOTHER SURGE OF RAIN WILL LIKELY AFFECT AREAS ALONG AND SOUTH OF I-90...BUT APPEARS HEAVIEST RAIN WILL STAY SOUTH OF THE AREA. FORECAST QPF AMOUNTS FROM TONIGHT THROUGH SATURDAY NIGHT SHOULD AMOUNT TO AROUND A QUARTER INCH ACROSS THE SOUTH. WILL NEED TO CONTINUE TO MONITOR RIVER LEVELS AND KEEP AN EYE ON OVERLAND FLOODING POTENTIAL INTO THE WEEKEND. FOR LATEST DETAILED INFORMATION CONCERNING RIVER LEVELS AND POTENTIAL FLOODING...SEE OUR HYDROLOGIC STATEMENTS. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...DENSE FOG ADVISORY UNTIL 11 AM CST FRIDAY FOR WIZ029-WIZ032- WIZ033-WIZ034-WIZ041-WIZ042-WIZ043-WIZ044-WIZ053-WIZ054- WIZ055-WIZ061. MN...DENSE FOG ADVISORY UNTIL 11 AM CST FRIDAY FOR MNZ079-MNZ086- MNZ087-MNZ088-MNZ094-MNZ095-MNZ096. IA...NONE. && $$ SHORT/LONG TERM...DAS AVIATION..........DTJ HYDROLOGY.........DAS UPDATE............RRS WWWW