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000 FXUS63 KMPX 250929 AFDMPX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN 329 AM CST WED NOV 25 2009 .DISCUSSION... MAIN FORECAST CONCERNS ARE IN THE NEXT 24 TO 36 HRS AND CENTER AROUND PRECIP TYPE AND AMOUNTS AS WELL AS WINDS. EARLY MORNING WATER VAPOR IMAGERY SHOWS THE UPPER LOW THAT BROUGHT DREARY WEATHER THE PAST FEW DAYS NOW ROTATING EASTWARD ACROSS NORTHERN ILLINOIS AND INDIANA. ANOTHER DEEP TROUGH IS WORKING SOUTHEASTWARD ACROSS NORTH DAKOTA TOWARDS MINNESOTA. FURTHER WEST...RIDGING HAS AMPLIFIED OVER EASTERN BRITISH COLUMBIA AND WESTERN ALBERTA IN RESPONSE TO A DEEP UPPER LOW JUST OF THE B.C. AND ALASKA COASTS. AS MENTIONED ABOVE...THE MOST ACTIVE PERIOD OF THE FORECAST WILL BE OVER THE NEXT 24 TO 36 HRS WITH A RESPITE ARRIVING FOR THANKSGIVING AND CONTINUING INTO THE WEEKEND. AFTER THAT...THE PATTERN LOOKS TO BECOME MORE ACTIVE AGAIN...BUT THERE IS ONLY SUPPORT FOR LOW POPS INTO EARLY NEXT WEEK. TODAY AND TONIGHT...THE FORECAST AREA IS IN THE COL AREA BETWEEN THE UPPER LOW TO THE EAST AND THE APPROACHING UPPER LOW TO THE WEST. A NARROW AREA OF CLEAR SKIES HAS DEVELOPED BETWEEN THE TWO SYSTEMS ACROSS THE CENTRAL PART OF THE AREA AND WILL CONTINUE TO TRANSLATE EASTWARD. A BAND OF MID LEVEL CONVERGENCE/FRONTOGENESIS CONTINUES TO FORCE A BAND OF RAIN WHICH IS NOW RIGHT ALONG THE MN/WI BORDER AND SLOWLY MOVING EAST. THIS WILL CONTINUE EAST THIS MORNING BUT WILL LIKELY BEGIN TO DECREASE IN COVERAGE/INTENSITY THROUGH MID MORNING. RADAR MOSAIC SHOWS RAIN/SNOW SHOWERS MOVING ACROSS SOUTHEASTERN NORTH DAKOTA INTO WEST CENTRAL MINNESOTA AS THE UPPER TROUGH APPROACHES. OVERALL THIS SYSTEM WILL TRACK A BIT FURTHER WEST THAN FORECAST YESTERDAY. THIS WILL HAVE AN IMPACT ON THERMAL PROFILES AND THEREFORE PRECIP TYPE THROUGH TONIGHT. PRECIPITATION WILL SPREAD INTO THE WESTERN CWA OVER THE NEXT FEW HOURS. WITH THE LOW TRACKING SOUTHEASTWARD ACROSS FAR SOUTHWEST MN... AREAS ALONG AND SOUTH OF THE MN RIVER VALLEY WILL BE IN POSITION TO TO RECEIVE THE STEADIEST PRECIPITATION THIS MORNING...WITH RADAR TRENDS SUPPORTING THIS. DRY AIR WILL WRAP INTO THE LOW WITH TIME THIS MORNING SO SIZABLE BREAKS IN THE PRECIPITATION ARE EXPECTED ACROSS THE SOUTHWEST AND SOUTH AROUND MIDDAY. THE UPPER LOW WILL BECOME BETTER ORGANIZED AS IT DIVES INTO CENTRAL IOWA EARLY THIS AFTERNOON. FORCING WILL INCREASE AS THIS OCCURS WITH INCREASED Q-VECTOR CONVERGENCE SHOWING UP IN THE MID LEVELS AND POTENTIAL VORTICITY ANOMALY TAKING ON MORE DEFINITION OVER SOUTHERN MINNESOTA. THEREFORE EXPECT THE BEST COVERAGE AND HIGHEST INTENSITY PRECIPITATION THIS AFTERNOON AND CONTINUE INTO THE EARLY EVENING. THE FAVORED AREA WILL BE THE SOUTHEAST THIRD OR SO OF THE CWA ALONG AND EAST OF I-35 AND SOUTH OF I-94 OR FROM THE SOUTHERN TWIN CITIES METRO SOUTH-SOUTHWEST TO WASECA AND ALBERT LEA AND FROM THE SOUTHERN TWIN CITIES SOUTHEAST TO RED WING AND TOWARDS EAU CLAIRE. OVERALL THE HEAVIEST PRECIP WILL BE JUST SOUTHEAST OF THE CWA. PRECIPITATION TYPE IS THE NEXT ISSUE. AS MENTIONED ABOVE...WITH THE LOW FURTHER WEST THE COLD AIR WILL NOT ADVANCE AS FAR EAST AS QUICKLY AND WARM AIR WRAPPING AHEAD OF THE LOW WILL BE ABLE TO WORK WESTWARD INTO THE EASTERN HALF OF THE CWA TODAY. MID LEVEL TEMPS/THICKNESSES ARE COLD ENOUGH TO SUPPORT SNOW BUT MODEL FORECAST SOUNDINGS SHOW MUCH WARMER LOW LEVEL AIR THAN RECENT DAYS. WILL STICK WITH SNOW ACROSS THE WESTERN QUARTER TO THIRD OF THE AREA THIS MORNING BASED ON CURRENT TRENDS. WITH COLUMN TEMPS WARMER TO THE EAST RAIN/SNOW MIX WILL BE MORE PREVALENT...ESPECIALLY THIS MORNING ACROSS EAST CENT MN WITH CONTINUED DRIZZLE/LIGHT RAIN ACROSS WEST CENT WI IN CONJUNCTION WITH THE BAND NOTED ABOVE. WITH FORCING INCREASING THIS AFTERNOON PRECIPITATION INTENSITY MAY BE JUST STRONG ENOUGH TO TRANSITION PRECIP TO ALL SNOW ACROSS EAST CENT MN BY LATE AFTERNOON WHILE RAIN WITH A MIX OF RAIN/SNOW AND POSSIBLY SOME ICE PELLETS WILL BE UNDERWAY ACROSS WEST CENT WI WITH THE BETTER CHANCE FOR A MIX COMING LATE IN THE AFTERNOON AND EARLY THIS EVENING. COLD AIR WILL MAKE QUICKER FORWARD PROGRESS THIS EVENING BUT PRECIP WILL BE WINDING DOWN. AS FAR AS SNOW ACCUMULATION GOES...THIS WILL BE TOUGH BUT AN INCH OR SO WILL BE POSSIBLE WHERE SNOW IS MOST PERSISTENT ACROSS SOUTH CENTRAL MN AND NORTHEASTWARD TOWARDS THE FAR SOUTHERN TWIN CITIES METRO AND RED WING. SHOULD PRECIP BECOME ALL SNOW EARLIER THAN CURRENTLY FORECAST THEN 2 INCH AMOUNTS ARE POSSIBLE BUT THIS IS LOOKING LESS LIKELY. NORTHWEST WINDS WILL INCREASE MARKEDLY IN THE WEST THIS MORNING BEFORE SPREADING SOUTHEASTWARD. BASED ON THE PATH OF THE LOW AND EXPECTED PATH OF HIGHER TROP PRESSURES THE STRONGEST WINDS WILL BE IN THE FAR SOUTHWEST BUT ALL AREAS WILL BE BREEZY BY EVENING. STRONGEST SUSTAINED WINDS OF 20 TO 25 MPH ARE EXPECTED FAR WEST WITH GUSTS OVER 30 MPH. THURSDAY THROUGH SATURDAY...THE UPPER LOW WILL BE MOVING ACROSS THE OHIO VALLEY THURSDAY MORNING. SFC HIGH PRESSURE WILL BE BUILDING EASTWARD INTO THE AREA WHILE THE WESTERN RIDGE PUSHES EASTWARD INTO THE DAKOTAS. IT WILL BE A MUCH COOLER DAY THAN THE AREA HAS SEEN IN A WHILE WITH HIGHS ONLY IN THE LOWER TO MID 30S THANKS TO H85 AIR IN THE -4 TO -6 C RANGE AND A BRISK NORTHWESTERLY WIND. WINDS WILL SLACKEN IN THE AFTERNOON THOUGH...AS THE SFC RIDGE AXIS REACHES THE FORECAST AREA. THE UPPER RIDGE WILL BECOME RE-ORIENTED OFF TO THE WEST RESULTING IN SLIGHTLY FLATTER UPPER FLOW OVERHEAD LOCALLY BUT WARM ADVECTION WILL STILL GET UNDERWAY THURSDAY NIGHT AHEAD OF A WEAK TROUGH. THIS LOOKS TO ONLY RESULT IN SOME INCREASED CLOUD COVER AND A REDUCED TEMPERATURE DECREASE INTO FRIDAY MORNING. A SHARPER UPPER RIDGE WILL CROSS THE AREA SATURDAY KEEPING DRY WEATHER IN PLACE. SATURDAY NIGHT THROUGH SUNDAY NIGHT...AN UPPER TROUGH WILL BE MOVING ACROSS SOUTHERN CANADA SATURDAY NIGHT BRINGING FALLING SFC PRESSURES AHEAD OF IT. MAIN LOW CIRCULATION WILL BE WELL OFF TO THE NORTH WITH A TROUGH AXIS EXTENDING SOUTHWARD INTO THE PLAINS. ENOUGH UPPER FORCING WILL BE IN PLACE TO SUPPORT SOME PRECIPITATION POTENTIAL TOWARDS SUNDAY MORNING BUT NOTHING SIGNIFICANT IS EXPECTED AT THIS TIME. MODEL DISAGREEMENT REMAINS WITH THE EVOLUTION AND PATH OF THE UPPER LOW INTO MONDAY. WILL KEEP THE GOING FORECAST AS IS FOR NOW BUT LOW POPS MAY BE NEEDED SUNDAY NIGHT AND MONDAY. ..MDB.. && .AVIATION... /06Z TAF ISSUANCE/ AN INVERTED TROUGH OVER FAR WESTERN WI WILL BE THE FOCUS FOR IFR/LOW MVFR CONDITIONS AT KRNH AND KEAU THROUGH MUCH OF THE UPCOMING TAF PERIOD. DRIZZLE WILL BE COMMON THROUGH THE MORNING THEN MORE OF A STEADY RAIN WILL DEVELOP AS A STRONG LOW PRESSURE SYSTEM ALOFT APPROACHES FROM NORTH DAKOTA. PROFILE DATA INDICATES THE RAIN SHOULD MIX WITH SNOW TOWARD EVENING WITH A PERIOD OF LIGHT SNOW BEFORE IT ENDS WEDNESDAY NIGHT. IFR/LIFR CONDITIONS ACROSS EASTERN MN...INCLUDING KMSP...SHOULD IMPROVE SOME OVERNIGHT AS DRIER AIR WORKS IN BEHIND THE INVERTED SURFACE TROUGH TO THE EAST. SOME POTENTIAL THAT KMSP COULD BE VFR BETWEEN 12Z AND 15Z BEFORE THE NEXT UPSTREAM SYSTEM BRINGS A LOWERING OF CEILINGS AND VISIBILITIES. LIGHT RAIN SHOULD DEVELOP AT KMSP BY MID MORNING AND PERSIST THROUGH THE AFTERNOON. AS COLDER AIR FILTERS IN...THE RAIN SHOULD MIX WITH OR CHANGE TO SNOW LATE IN THE AFTERNOON AND LAST INTO THE EARLY EVENING BEFORE ENDING. KSTC IS CURRENTLY ON THE VERGE OF CLEARING. HOWEVER...POTENTIAL IS HIGH FOR IFR/LIFR IN FOG WITH VERY MOIST LOW LEVEL CONDITIONS IN PLACE. CLEARING WILL NOT LAST LONG AS MID LEVEL MOISTURE SPREADS IN BEFORE DAYBREAK WITH LIGHT SNOW LIKELY DURING THE MORNING AS A STRONG LOW PRESSURE SYSTEM ALOFT PASSES BY. IMPROVING CONDITIONS FOR KSTC DURING THE LATE AFTERNOON ALONG WITH NORTHWEST WINDS AT 15 TO 25 KNOTS. ALTHOUGH KAXN AND KRWF ARE CURRENTLY VFR...THEY ARE ALREADY SEEING MID/HIGH LEVEL MOISTURE INCREASE AHEAD OF THE UPPER LOW OVER NORTH DAKOTA. LIGHT SNOW SHOULD DEVELOP/SPREAD INTO BOTH SITES BETWEEN 09Z AND 12Z AND THEN CONTINUE DURING THE MORNING WITH IFR/LOW MVFR CONDITIONS OCCURRING. NORTHWEST WINDS WILL BE ON THE INCREASE BY 17Z WITH 16-18 KNOTS SUSTAINED GUSTING TO 30 KNOTS OR SO FOR THE AFTERNOON. ONLY FLURRIES EXPECTED FOR THE AFTERNOON WITH CEILINGS LIFTING TO NEAR 3000 FEET. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...NONE. WI...NONE. && $$ MDB/RAH
