FXUS63 KDTX 252343
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
643 PM EST WED NOV 25 2009
.AVIATION...
A LOW PRESSURE SYSTEM OVER THE EASTERN UPPER PENINSULA WILL SLOWLY
MOVE EASTWARD TONIGHT AND THURSDAY. AS THE LOW MOVES EAST IT WILL
DRAG AN AREA OF WRAP AROUND RAIN FROM THE WESTERN GREAT LAKES
TONIGHT...WITH WIDESPREAD MVFR/ISOLATED IFR CONDITIONS MUCH OF THE
NIGHT. A DRY SLOT OF AIR WILL WORK ITS WAY INTO THE AREA AROUND
13Z ENDING THE RAIN AND BRINGING VFR/MVFR CONDITIONS TO MANY OF
THE TAF SITES. THE EXCEPTION WILL BE MBS...WHICH WILL BE THE PIVOT
POINT FOR THE RAIN AS RAIN SHOWERS AND MVFR CONDITIONS CONTINUE
THROUGH THURSDAY. ANOTHER BATCH OF RAIN WILL HEAD FOR THE TAF
SITES LATE IN THE AFTERNOON HOURS AS A TROF SWINGS THROUGH THE
CENTRAL GREAT LAKES. GIVEN THE LATE ARRIVAL OF THE NEXT BATCH OF
RAIN AND THE POSSIBILITY IT WILL NOT ARRIVE UNTIL AFTER 00Z WILL
LEAVE THE TAF SITES DRY LATE THURSDAY AFTERNOON.
&&
.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).
