Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 092328 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 628 PM EST TUE FEB 9 2010 .AVIATION...
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THE STORM SYSTEM NOW TRACKING ACROSS OHIO WILL ALLOW THE SOLID AREA OF LIGHT TO OCCASIONALLY MODERATE SNOW TO PERSIST THROUGH ROUGHLY 09Z BEFORE WANING AS THE STORM DEPARTS TO THE EAST. FOR THE MOST PART...VISIBILITIES WILL RANGE FROM THREE QUARTERS TO A MILE...WITH PERIODS OF VISIBILITIES AT OR BELOW A HALF A MILE. CEILINGS ARE A BIT HIGHER /MAINLY IN THE IFR AND MVFR RANGE/ THANKS TO SOME FEED OF DRIER AIR NEAR THE SURFACE UNDER GUSTY NORTHEASTERLY WINDS WHICH SHOULD PERSIST THROUGH THE NIGHT. ACCUMULATING SNOWFALL WILL CONTINUE THROUGH THE REST OF THE EVENING AND INTO THE OVERNIGHT. THE STORM IS ACTUALLY EXPECTED TO UNDERGO SOME STRENGTHENING IN THE 00Z TO 06Z TIME PERIOD BEFORE BEGINNING ITS DOWNWARD TREND. GUSTY NORTHEAST WINDS WILL VEER TO THE NORTH OVERNIGHT AND CONTINUE INTO WED AFTERNOON WITH FREQUENT GUSTS OVER 20 KNOTS. THIS WILL CREATE A PROLONGED PERIOD OF BLOWING AND DRIFTING SNOW.
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&& .PREV DISCUSSION...
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ISSUED 401 PM EST TUE FEB 9 2010 SHORT TERM...THIS AFTERNOON AND TONIGHT WINTER STORM WARNINGS AND WINTER WEATHER ADVISORIES REMAIN IN EFFECT UNTIL WEDNESDAY MORNING. PLEASE SEE THE WINTER STORM WARNING/WINTER WEATHER ADVISORY /WSWDTX/ FOR EXACT TIMES AND ACCUMULATIONS. THE WINTER STORM IS UNDERWAY FOR SE MI. LIGHT SNOW HAS PERSISTED SINCE THIS MORNING WITH AREAS OF LOCALLY HEAVIER SNOW MOVING THROUGH AT TIMES. THIS HAS LEAD TO SNOWFALL TOTALS OF 3-4 INCHES NEAR THE OHIO BORDER DECREASING NORTHWARD TO ABOUT 2 INCHES UP THROUGH SAGINAW. MODELS STILL HAVE A GOOD HANDLE ON THIS DEEPENING SURFACE LOW CURRENTLY LOCATED OVER SOUTHWEST OHIO WITH ITS ASSOCIATED UPPER LOW LAGGING SLIGHTLY TO THE WEST OVER SOUTHERN ILLINOIS. THIS UPPER LOW IS FORECAST TO TRACK DUE EAST TOWARD THE ATLANTIC COAST BY WED AFTERNOON WHICH PHASES IT WITH THE STRONG 180KT SOUTHERN BRANCH OF THE JET STREAM. THIS CAUSES THE SURFACE LOW TO OCCLUDE AND WEAKEN ON THE NORTH SIDE OVER THE GREAT LAKES AND RESTRENGTHEN TO THE SOUTH NEAR THE MID-ATLANTIC STATES. THIS KEEPS THE BEST LARGE SCALE ASCENT TO OUR SOUTH...BUT WE WILL STILL BE IN A REGION OF MODERATE LIFT AND DECENT SNOWFALL INTENSITIES AS THE MID LEVEL DEFORMATION BAND SETS UP AND PIVOTS OVER SE MI. LATEST MODELS CONTINUE TO PLACE THIS FEATURE ACROSS THE I-69 CORRIDOR AROUND 00Z-06Z. ISENTROPIC ACCENT ALSO INCREASES OVER THE AREA AS THE TROWEL AXIS LIFTS NORTH THIS AFTERNOON. THE GFS/NAM/ECMWF AND RUC ALL AGREE WITH THE GENERAL STRENGTH AND LOCATION OF THIS STORM. MODEL QPF CONTINUE TO RANGE FROM .4 IN THE SAGINAW VALLEY UP TO .7 NEAR THE OHIO BORDER. THIS IN CONJUNCTION WITH SNOW RATIOS BETWEEN 12:1 TO 15:1 KEEPS THE CURRENT FORECAST IN LINE WITH PREVIOUS THINKING OF 5-9 INCHES IN THE WARNING AREA AND 3-6 IN THE NORTH WHERE WE ARE UNDER A WINTER WEATHER ADVISORY. NORTHEAST WINDS MAKE LAKE ENHANCEMENT A POSSIBILITY OVER THE EASTERN THUMB REGION OVERNIGHT AND TOMORROW. NAM12 SHOWS A CONVERGENT BAND SETTING UP AROUND 03Z. THE LOCATION OF THIS BAND WILL MOST LIKELY RAISE SNOWFALL TOTALS IN THIS REGION WHICH HAD BEEN TAKEN INTO ACCOUNT FOR STORM TOTALS. THESE WINDS WILL INCREASE...GUSTING UP TOWARD 30KTS...AND BECOME MORE NORTHERLY OVERNIGHT. THIS WILL CREATE PERIODS OF BLOWING SNOW AND MAY CAUSE DRIFTS TO FORM. LONG TERM...WEDNESDAY THROUGH NEXT TUESDAY THE EXPIRATION TIMES LOOK GOOD ON THE CURRENT PACKAGE OF WINTER HEADLINES. THEY WILL BE NEEDED INTO WEDNESDAY AS SNOW IS EXPECTED TO LINGER THROUGH AT LEAST THE FIRST HALF OF THE MORNING AFTER SUNRISE, AND EVEN LONGER IN THE THUMB WHERE LAKE EFFECT WILL REMAIN INVOLVED, ALTHOUGH IT WILL BE MORE MODEST BY THEN COMPARED TO THE POTENTIAL TONIGHT. THE LARGER SCALE PATTERN OF SNOW WILL ALSO BE ON THE DECLINE, BUT WHAT IS LEFT WILL COMBINE WITH STRONG NORTH WINDS AND BLOWING SNOW THAT WILL RESULT IN HAZARDOUS CONDITIONS DURING THE MORNING HOURS AND INTO THE EARLY AFTERNOON IN THE THUMB REGION. MODEL DATA ON THE WEAKENING TROWAL/OCCLUSION FORCING LOOKS GOOD DURING THE MORNING. IT SHOULD BE WELL UNDERWAY BY SUNRISE AND WILL CONTINUE TO WEAKEN AND SHRINK TOWARD THE EAST AS THE UPPER LEVEL CIRCULATION MOVES TOWARD THE ATLANTIC COAST. THIS WILL LEAVE A GENERAL WEAK DEFORMATION PATTERN IN THE MID LEVELS THAT WILL HELP SUPPORT LIGHT SNOW OR FLURRIES OVER THE REGION AS THE STORM SYSTEM RUNS ITS COURSE. AS THIS OCCURS, THE NORTH WINDS ON THE HEELS OF THE SYSTEM WILL BE STRONGLY ONSHORE INTO THE THUMB FROM LAKE HURON. SURPRISINGLY, THE LAKE EFFECT POTENTIAL LOOKS LIMITED BY WARM AIR MOVING IN FROM ONTARIO IN THE FORM OF SINGLE DIGIT 850 MB TEMPERATURES. MODEL FORECAST SOUNDINGS SHOW COLDER AIR BELOW THAT, CLOSER TO -13C CENTERED AROUND 900 MB, BUT THAT JUST INDICATES EQUILIBRIUM LEVELS AROUND 3500 FEET DURING THE PEAK OF THE ONSHORE FLOW. GIVEN THIS MODEST CONTRIBUTION, THE ADDITIONAL INCH OR TWO LOOKS GOOD IN OUR GOING FORECAST FOR THE THUMB WITH AN ADDITIONAL INCH OR LESS OVER THE REST OF SE MICHIGAN ON WEDNESDAY. NOTHING MORE THAN A FLURRY IS THEN EXPECTED FROM THE MID LEVEL MOISTURE LINGERING OVER THE AREA WEDNESDAY NIGHT. THIS CLOUD COVER WILL DO MORE TO TAKE THE EDGE OFF OF THE NORTHWEST WINDS AND ANY COLDER AIR CARRIED INTO THE REGION. LOW LEVEL TEMPERATURE FIELDS IN THE MODEL DATA SHOW THIS NICELY AS A WARM SHADOW OF THE GREAT LAKES, WHICH WILL BE REFLECTED AS A RELATIVELY NARROW 5 TO 10 DEGREE DIURNAL TEMPERATURE RANGE RIGHT INTO THURSDAY. IT DOES LOOK LIKE THE CLOUDS WILL START TO BREAK UP DURING THURSDAY AFTERNOON DUE TO WEAKLY CONFLUENT FLOW ALOFT AND WEAK NORTHWEST FLOW IN THE LOW LEVELS BUT CONFIDENCE IS NOT THAT GREAT UNTIL THURSDAY NIGHT INTO FRIDAY WHEN A SHORT WAVE RIDGE ALOFT AND SURFACE HIGH PRESSURE TAKE GREATER CONTROL. AT LEAST IT WILL BE DRY THROUGH THE END OF THE WEEK. A WAVE FROM CENTRAL CANADA IS THEN EXPECTED TO SET OFF A NEW ROUND OF LARGER SCALE HEIGHT FALLS OVER THE GREAT LAKES ON FRIDAY INTO SATURDAY. IT IS NO SURPRISE THAT THE LATEST GLOBAL MODELS HAVE A WIDE VARIETY OF OPINIONS ON THE SMALL SCALE DETAILS DURING THIS TIME, MAINLY ON THE LEAD WAVE. THEY ARE IN CLOSER AGREEMENT ON THE PRESENCE OF THE COMPACT CLOSED CIRCULATION MOVING INTO THE GREAT LAKES AROUND SATURDAY, BUT THERE IS ENOUGH SPREAD IN THE TIMING OF THIS SYSTEM TO DO LIKEWISE WITH THE CHANCE OF SNOW DURING THE WEEKEND. IF IT IS NOT FOR THIS WAVE, IT WILL BE FOR THE PRESENCE OF THE LARGE SCALE UPPER LOW/TROUGH OVER THE GREAT LAKES. DEEP NORTHWEST FLOW IN THE LOW LEVELS ASSOCIATED WITH THIS PATTERN WILL KEEP TEMPERATURES ON THE COLD SIDE OF NORMAL INTO EARLY NEXT WEEK. MARINE... DEEPENING LOW PRESSURE WILL TRACK ACROSS OHIO THIS EVENING AND INTO LAKE ERIE OVERNIGHT. THIS WILL STRENGTHEN THE NORTHEASTERLY GRADIENT OVER LAKE HURON...LEADING TO FREQUENT GUSTS UP TO 35 KNOT GALES. THESE WINDS WILL CONTINUE INTO WEDNESDAY AFTERNOON BEFORE HIGH PRESSURE BUILDS IN FROM THE WEST AND RELAXES THE GRADIENT.
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&& .DTX WATCHES/WARNINGS/ADVISORIES...
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MI...WINTER STORM WARNING...MIZ060-MIZ061-MIZ068-MIZ069-MIZ070-MIZ075- MIZ076-MIZ082-MIZ083...UNTIL 10 AM WEDNESDAY. WINTER STORM WARNING...MIZ055-MIZ062-MIZ063...UNTIL 1 PM WEDNESDAY. WINTER WEATHER ADVISORY...MIZ047-MIZ048-MIZ053...UNTIL 7 AM WEDNESDAY. WINTER WEATHER ADVISORY...MIZ049-MIZ054...UNTIL 1 PM WEDNESDAY. LAKE HURON... GALE WARNING...LHZ362-LHZ363-LHZ421-LHZ422-LHZ441-LHZ442-LHZ443- LHZ462-LHZ463-LHZ464...UNTIL 7 PM WEDNESDAY. LAKE ST CLAIR... WINTER STORM WARNING...LCZ423...UNTIL 10 AM WEDNESDAY. BRISK WIND ADVISORY...UNTIL 4 PM WEDNESDAY. MI WATERS OF LAKE ERIE... BRISK WIND ADVISORY...UNTIL 4 PM WEDNESDAY.
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&& $$ AVIATION.....SC SHORT TERM...DRK LONG TERM....BT MARINE.......DRK/SC YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).

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