000 FXUS63 KDTX 260450 AFDDTX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI 1150 PM EST WED NOV 25 2009 .AVIATION... A LOW PRESSURE SYSTEM OVER THE EASTERN UPPER PENINSULA WILL SLOWLY MOVE EASTWARD TODAY...THEN MOVE TOWARDS THE EASTERN GREAT LAKES TONIGHT. AN AREA OF RAIN AHEAD OF A SHORTWAVE WILL BRING RAIN TO THE TAF SITES EARLY THIS MORNING WITH WIDESPREAD MVFR/ISOLATED IFR CONDITIONS. A DRY SLOT WILL WORK ITS WAY INTO THE AREA BEHIND THIS RAIN...DRYING OUT MUCH OF THE TAF SITES LATER THIS MORNING AND INTO THE AFTERNOON HOURS BRINGING VFR/MVFR CONDITIONS TO THE AREA. THE EXCEPTION WILL BE MBS...WHICH WILL BE THE PIVOT POINT FOR THE RAIN AS RAIN SHOWERS AND MVFR CONDITIONS CONTINUE THROUGH MUCH OF THE DAY. ANOTHER BATCH OF RAIN ASSOCIATED WITH THE WRAP AROUND MOISTURE WITH THE DEPARTING LOW WILL HEAD INTO THE TAF SITES AROUND 00Z. WHILE THE METRO AIRPORTS SHOULD BE WARM ENOUGH FOR ALL RAIN...SOME SNOW COULD MIX IN ACROSS THE REST OF THE TAF SITES AS COLD AIR ADVECTS IN FROM THE WEST. THE WRAP AROUND PRECIPITATION WILL BRING THE RETURN OF WIDESPREAD MVFR CONDITIONS TO THE TAF SITES THIS EVENING. && .PREV DISCUSSION...ISSUED 343 PM EST WED NOV 25 2009 SHORT TERM...TONIGHT MID LEVEL WAVE CURRENTLY OVER SOUTHEAST LOWER MICHIGAN IS PRODUCING AREAS OF LIGHT SHOWERS AND DRIZZLE. THIS WILL BE EXITING THE AREA THIS EVENING. A SECOND STRONGER WAVE OVER IOWA WILL ROTATE INTO MICHIGAN OVERNIGHT PUSHING AN ELEVATED COLD FRONT THROUGH EARLY TONIGHT KEEPING THE BOUNDARY LAYER RELATIVELY WARM. THIS WILL CONTINUE THE AREAS OF LIGHT SHOWERS AND DRIZZLE. TEMPERATURES WILL DROP INTO THE UPPER 30S TO LOWER 40S. LONG TERM...THANKSGIVING THROUGH NEXT WEDNESDAY CONDITIONS FOR THANKSGIVING WILL NOT BE THAT GREAT AESTHETICALLY BUT WILL BE BEARABLE OTHERWISE AS WE WILL SPEND MOST OF THE DAY IN THE DRY SLOT OF THE LOW PRESSURE SYSTEM OVER THE GREAT LAKES. BOUNDARY LAYER MOISTURE PROFILES ARE UNFAVORABLE FOR DRIZZLE AND THERE COULD EVEN BE A FEW BREAKS IN THE CLOUDS AT TIMES. THIS SUGGESTS LEANING TEMPERATURES CLOSE TO GUIDANCE HIGHS IN THE MID 40S FOR MOST AREAS, ESPECIALLY WITH A SOUTHWEST WIND. THINGS GET MORE INTERESTING THURSDAY NIGHT AS THE UPPER LEVEL SYSTEM EVOLVES INTO A STRONG PATTERN OF MID LEVEL DEFORMATION OVER LOWER MICHIGAN. ALL OF THE 12Z MODELS HAVE A GOOD HANDLE ON THIS FORCING USING 500 MB VORTICITY AS A PROXY FOR THE DYNAMICS IN THE WIND FIELD. PREFER THE SOLUTIONS THAT SHOW GREATER COVERAGE AND AMOUNTS OF PRECIPITATION DUE TO THE TENDENCY FOR THESE PATTERNS TO OVERACHIEVE WITH A GIVEN AMOUNT OF MOISTURE. AT THE SAME TIME, WE ARE NOT READY TO GO ANY HIGHER THAN THE GFS SOLUTION FOR QPF IN SE MICHIGAN. THE DEFORMATION AND LIFT ARE SHOWN TO OCCUR IN A RELATIVELY STABLE ENVIRONMENT JUDGING FROM CROSS SECTIONS OF THETA-E. MOISTURE ALSO LOOKS LIKE A LIMITING FACTOR WITH SPECIFIC HUMIDITY RUNNING AROUND 1G/KG. THERE IS ALSO THE QUESTION OF PRECIPITATION TYPE WHICH LOOKS LIKE IT WILL BE ALL RAIN OR A MIX OF RAIN AND SNOW DURING THE EVENING. MODEL FORECAST SOUNDINGS INDICATE A WARM BOUNDARY LAYER WELL INTO THE OVERNIGHT WITH THE BEST CHANCE OF ALL SNOW OCCURRING ON THE HEELS OF THE PRECIPITATION PATTERN. THE BEST WORDING AT THIS POINT CALLS FOR RAIN AND SNOW LIKELY AFTER MIDNIGHT WITH PERHAPS A COATING OF GRASSY ACCUMULATION BY SUNRISE FRIDAY MORNING. AFTER A LINGERING CHANCE OF LIGHT RAIN AND SNOW FRIDAY MORNING, THE REST OF THE DAY WILL BE DRY BUT IT WILL BE COLDER. MODEL THICKNESS IN THE 1000-850 MB LAYER IS AROUND 1296DM THROUGH THE DAY AND SUGGESTS A STRUGGLE FOR TEMPERATURES TO BREAK INTO THE 40S. A STIFF NORTHWEST WIND AND PLENTIFUL CLOUD COVER WILL ALSO WORK AGAINST MUCH OF A TEMPERATURES RISE. DRY CONDITIONS ARE THEN EXPECTED TO LAST THROUGH SATURDAY AS WEAK SURFACE HIGH PRESSURE MOVES QUICKLY THROUGH THE REGION AND WARM ADVECTION GETS UNDERWAY AGAIN. EXPECT AN AGGRESSIVE WARMING TREND TO TAKE HOLD DURING THIS TIME THAT WILL LAST INTO SUNDAY. THIS WILL BE THANKS TO RAPID DEVELOPMENT OF ZONAL FLOW IN THE LONG WAVE PATTERN BUT WITH THE UPPER RIDGE GUARDING LOWER MICHIGAN AS IT WEAKENS WITH TIME. AS IS TYPICAL OF ZONAL FLOW, IT WILL BE SHORT LIVED. THERE IS GOOD AGREEMENT AMONG THE GLOBAL MODELS ON A NEW ROUND OF AMPLIFICATION TAKING PLACE DURING SUNDAY AND MONDAY AND GOOD AGREEMENT ON THE NEW LARGER SCALE TROUGH FORMING OVER THE CENTRAL PLAINS. CONSIDERING THE TROUGH AXIS WILL REMAIN TO OUR WEST THROUGH MOST OF MONDAY, THERE IS SOME CONFIDENCE IN THE PROSPECTS OF MODERATING TEMPERATURES LASTING THAT LONG BUT AT THE EXPENSE OF WET AND UNSETTLED CONDITIONS. SOME CONVERGENCE OF SOLUTIONS HAS TAKEN PLACE IN THE 12Z RUNS REGARDING THE EVOLUTION OF THE PLAINS TROUGH DURING TUESDAY AND WEDNESDAY. THE NEW LONG WAVE AMPLIFICATION FROM THE NORTH PACIFIC INTO NORTH AMERICA DURING THE EARLY PART OF NEXT WEEK FAVORS A PROGRESSIVE NATURE OF THE PLAINS TROUGH IN A SHORT WAVE SENSE WITH A NEW SHORT WAVE DROPPING INTO THE PLAINS TO MAINTAIN THE LONG WAVE TROUGH/UPPER LOW DURING THE MID WEEK PERIOD. THIS WOULD BE THE CASE REGARDLESS OF HOW MUCH SPLIT FLOW DEVELOPS AND HOW STRONG THE SOUTHERN STREAM WAVE MAY BECOME. THE PASSAGE OF THE LEAD NORTHERN STREAM WAVE THROUGH THE GREAT LAKES WILL BRING A RETURN TO COLDER TEMPERATURES DURING THAT TIME BUT WITH ODDS IN OUR FAVOR FOR DRY CONDITIONS, ESPECIALLY GIVEN THE STRONG TREND OF THE 12Z GFS IN THAT DIRECTION. MARINE... LOW PRESSURE NEAR THE STRAITS WILL MAINTAIN SOUTHWEST WINDS 20 KNOTS OR LESS OVER THE MARINE AREAS TONIGHT THROUGH MOST OF THANKSGIVING. A COLD FRONT WILL THEN MOVE THROUGH LAKE HURON AND LOWER MICHIGAN THURSDAY NIGHT AND BRING A ROUND OF STRONGER NORTHWEST WINDS ON FRIDAY. THE COLDER AIR AND STRONGER WINDS WILL BUILD THE WAVES ENOUGH OVER SOUTHERN PORTIONS OF LAKE HURON TO LIKELY REQUIRE A SMALL CRAFT ADVISORY. SURFACE HIGH PRESSURE WILL THEN BUILD QUICKLY THROUGH THE REGION ON SATURDAY AND ENSURE DRY CONDITIONS. MILDER SOUTHWEST WINDS WILL THEN LAST THROUGH THE REST OF THE WEEKEND. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....KURIMSKI SHORT TERM...DRC LONG TERM....BT MARINE.......DRC/BT YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).