FXUS63 KDTX 052302
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
602 PM EST SAT DEC 5 2009

.AVIATION...

THE BLANKET OF STRATO CU ACROSS MOST OF SOUTHERN MICHIGAN IS BASED 
PRIMARILY BETWEEN 4K AND 5K FEET. SOME LOWER BASED CLOUDS ALONG WITH 
SOME FLURRIES HAVE HOWEVER BEEN IMPACTING THE SAGINAW VALLEY FROM 
TIME TO TIME DUE TO THE SOUTHWESTERLY MOISTURE FLUX OFF LAKE 
MICHIGAN. THESE CONDITIONS SHOULD PERSIST AT MBS THROUGH THE NIGHT 
AND INTO SUN MORNING GIVEN THE PERSISTENT SOUTHWEST FLOW. 
MEANWHILE...LOW LEVEL WARM AIR ADVECTION SHOULD HELP WEAKEN THE 
INVERSION FARTHER SOUTH. THIS IS EXPECTED TO LEAD TO AN OVERALL 
CLEARING TREND FROM PTK SOUTH INTO DETROIT THROUGH NIGHT.

&&

.PREV DISCUSSION...ISSUED 327 PM EST SAT DEC 5 2009 

SHORT TERM...TONIGHT

THE STRONGER SHORTWAVE WAS EXITING LAKE SUPERIOR...HOWEVER THE TAIL 
OF THIS WAVE WAS MOVING ACROSS LOWER MI...WHICH SPARKED THE INCREASE 
IN LAKE EFFECT OFF OF LAKE MICHIGAN AND GAVE A BIT OF BETTER SUPPORT 
FOR THE CU OVER MUCH OF SOUTHEAST MICHIGAN.  AS THIS WAVE LEAVES THE 
AREA THIS EVENING AND WE LOSE WHAT LITTLE DIURNAL HEATING WE 
HAD...THE CU FIELD WILL BEGIN TO DISSIPATE. WILL KEEP THE AFTERNOON 
FLURRIES GOING INTO THE EARLY EVENING UNTIL THAT WEAK WAVE HAS 
PASSED. 

ACROSS THE TRI CITIES AREA INTO THE THUMB...THAT REGION WILL 
BE MORE IN THE SW FLOW PLUME OFF OF LAKE MICHIGAN AND EXPECT SC TO 
STICK AROUND ALL NIGHT. THE PLUME SHOULD WEAKEN TONIGHT AS 850 MB 
TEMPS WARM TO AROUND -8C WHICH WILL WEAKEN THE OVER LAKE LAPSE 
RATES. 

A WEAK SHEARED SHORTWAVE MOVES ACROSS THE CENTRAL LAKES LATE 
TONIGHT. THAT WAVE BRINGS SOME MID AND UPPER LEVEL MOISTURE TO 
MAINLY THE NORTHERN FORECAST AREA...AND ALL OF THAT WITH THE PLUME 
OF LOW LEVEL MOISTURE FROM LAKE MI SHOULD BE ENOUGH TO HAVE FLURRIES 
THERE TOO. 

TEMPS OVERNIGHT WILL BE NEAR MOS NUMBERS. THERE IS POTENTIAL TO FALL 
BELOW THAT TONIGHT IN THE SOUTH PART OF THE FORECAST AREA IF THE 
CLOUDS DISSIPATE SOON ENOUGH AND ALLOW THE WINDS TO DECOUPLE BEFORE 
THE GRADIENT AND MID/UPPER CLOUDS INCREASE. THINKING THAT IS A LOT 
TO EXPECT GIVEN CURRENT SETUP AND WILL STICK CLOSE TO MOS.

LONG TERM...SUNDAY THROUGH SATURDAY

UPPER LOW PULLING EAST/NORTHEAST THROUGH THE NORTHERN GREAT LAKES ON 
INTO QUEBEC LATE TONIGHT INTO SUNDAY WILL COAX A LOW LEVEL FRONTAL 
BOUNDARY SOUTH THROUGH NORTHERN LOWER MICHIGAN/NORTHERN LAKE HURON. 
FOR SUNDAY...THIS BOUNDARY WILL ACT TO FOCUS SNOW SHOWERS MAINLY TO 
THE NORTH OF THE CWA...WITH JUST A CHANCE OF FLURRIES DOWN TO AROUND 
I 69. BY SUNDAY NIGHT INTO MONDAY...THIS FRONT WILL SETTLE ALONG THE 
NORTHERN EDGE OF THE CWA. AS A VIGOROUS SMALL SCALE SHORTWAVE LIFTS 
OUT OF THE SOUTHWEST CONUS UPPER TROUGH AND THEN RACES THROUGH THE 
CENTRAL PLAINS INTO THE GREAT LAKES...THIS BOUNDARY WILL AGAIN ACT 
AS A FOCUS TO ENHANCE THE FORCING INDUCED BY THIS WAVE...WHICH WILL 
PROVIDE THE POTENTIAL FOR SEVERAL INCHES OF SNOW SUNDAY NIGHT INTO 
EARLY MONDAY IN ADVANCE OF THE SHORTWAVE. THIS WOULD BE MOST LIKELY 
ACROSS THE FAR NORTHERN CWA...AND WILL LIMIT ANY ACCUMULATIONS OF AN 
INCH OR SLIGHTLY MORE TO THE SAGINAW VALLEY AND NORTHERN THUMB. AS 
THE SHORTWAVE CROSSES THE AREA MONDAY...A MORE GENERAL LIGHT SNOW 
WILL AFFECT MUCH OF THE AREA...WITH THIS BAND OF ENHANCED SNOWFALL 
LIFTING GRADUALLY NORTH OF THE AREA...BUT STILL PERHAPS PRODUCING 
AROUND ANOTHER INCH OR SO OF SNOW NORTH OF FLINT. AN INCH OR LESS 
WILL BE MORE COMMON FROM FLINT SOUTH.

THIS SYSTEM IS THE SMALLER OF THE TWO THAT WILL AFFECT THE AREA 
DURING THE EXTENDED PORTION OF THE FORECAST. A MUCH STRONGER LOW 
PRESSURE SYSTEM WILL LIFT INTO THE REGION TUESDAY NIGHT INTO 
WEDNESDAY AS A LARGER SHORTWAVE DISTURBANCE LIFTS OUT OF THE MEAN 
SOUTHWEST CONUS TROUGH AND TRACKS INTO THE CENTRAL GREAT LAKES.
THIS SYSTEM IS EXPECTED TO DEEPEN VERY QUICKLY AS IT CROSSES THE 
AREA AS IT WILL BE ENHANCED BY A WAVE WITHIN THE SUBTROPICAL JET
LIFTING ACROSS MEXICO INTO THE NORTHWEST GULF OF MEXICO. THE TRACK 
OF THIS SYSTEM WILL BE KEY TO HOW THIS SYSTEM WILL AFFECT LOWER 
MICHIGAN...AND AS IS OFTEN THE CASE...THERE REMAINS A FAIR AMOUNT
OF UNCERTAINTY 4 DAYS OUT FROM THE EVENT. 

SO WHAT CAN BE SAID ABOUT THE CHARACTER OF THIS STORM AT THIS TIME?
WITH THE "INGESTION" OF THE AFOREMENTIONED SUBTROPICAL WAVE...IT CAN 
BE SURMISED WITH SOME CONFIDENCE THAT THERE WILL BE AN IMPRESSIVE 
SLUG OF MOISTURE THAT LIFTS NORTH INTO THE AREA EARLY IN THE STORM 
EVOLUTION...PRIMARILY TUESDAY NIGHT. GIVEN THE COLD AIR THAT WILL BE 
IN PLACE...THIS SHOULD MEAN A QUICK SEVERAL INCHES OF SNOW (2-4 IN.) 
FOR MUCH OF THE REGION AS THE CENTER OF THE STORM APPROACHES. AFTER 
THAT...THE EXACT TRACK BECOMES MUCH MORE IMPORTANT AS THE LOW MOVES 
INTO THE GREAT LAKES. WITH THIS UPPER TROUGH POSITIONED SO FAR TO 
THE WEST...MODEL TRENDS TO BRING THIS LOW OVER THE AREA OR EVEN A 
BIT TO THE WEST SEEM REASONABLE...AND THE RAPID DEEPENING OF THE 
SYSTEM WOULD TEND TO REINFORCE THIS POSSIBILITY AS WELL. SUCH A 
TRACK WOULD TEND TO BRING THE WARM SECTOR OF THE STORM AT LEAST INTO 
THE SOUTHEAST QUADRANT OF THE CWA...CHANGING THE SNOW TO A RAIN/SNOW 
MIX...OR PERHAPS JUST A CHANGE TO DRIZZLE AS PART OF THE AREA COMES 
UNDER THE INFLUENCE OF THE DRY SLOT...LEAVING THE ONLY ABUNDANT 
MOISTURE AT THE LOWER LEVELS.

FURTHER NORTHWEST...THE AFFECT OF THIS WARM SECTOR/DRY SLOT WILL 
TEND TO BE MUTED...SO HEAVIER SNOW WILL HAVE A CHANCE OF LASTING 
LONGER INTO WEDNESDAY AS THE LOW TRACKS OVERHEAD...BRINGING MORE 
SNOWFALL ACCUMULATION. THE EXACT SOUTHEAST TO NORTHWEST GRADIENT 
OF THIS SNOWFALL WILL BE THE TRICKIEST ASPECT OF THE STORM SYSTEM 
AND THIS IS WHERE A BETTER FEEL FOR THE TRACK WILL BRING MORE 
CONFIDENCE TO THE FORECAST WITH TIME. 

SUFFICE IT TO SAY...THIS WILL LIKELY BE THE FIRST WINTER STORM TO 
AFFECT THE AREA THIS SEASON AND WILL LIKELY HAVE AN IMPACT ON TRAVEL 
AND OTHER ACTIVITY DURING THE MIDDLE OF NEXT WEEK.

BEYOND THAT...WINTER REALLY SETS IN OVER THE AREA AS MUCH COLDER AIR 
SPILLS INTO THE AREA FROM CANADA...AND PERSISTS INTO NEXT WEEKEND. 
PERIODS OF LAKE EFFECT SNOW CAN BE EXPECTED AS THIS COLD NORTHWEST 
TO WEST FLOW CONTINUES IN BEHIND THIS STORM SYSTEM AND BRINGS PLUMES 
OF MOISTURE OFF OF LAKE MICHIGAN INTO THE AREA. HIGH TEMPERATURES 
FROM THURSDAY INTO SATURDAY WILL BE LUCKY TO REACH 30 DEGREES WITH 
TEENS/20S COMMON FOR LOW TEMPERATURE TO END THIS FORECAST PERIOD.

MARINE...

SOUTHWEST WINDS WILL INCREASE AGAIN LATE TONIGHT AND INTO SUNDAY 
MORNING AS A WEAK SURFACE TROUGH PASSES TO THE NORTH. THE INCREASED 
WINDS AND LONG FETCH WILL PROBABLY BRING WAVES BACK UP TO SMALL 
CRAFT ADVISORY CRITERIA ACROSS THE SAGINAW BAY TO THE TIP OF THE 
THUMB. 

THERE IS A WEAKER AREA OF LOW PRESSURE FOR MONDAY...BUT FLOW WILL BE 
RATHER WEAK WITH THIS FEATURE.  THE NEXT GALE POTENTIAL WILL BE FOR 
TUESDAY NIGHT RIGHT INTO THURSDAY AS A VERY STRONG STORM DEEPENS 
OVER THE LAKES REGION.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...SAGINAW BAY...FROM 7 AM SUNDAY TO 7 PM 
     SUNDAY.

LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

AVIATION.....SC
SHORT TERM...RBP 
LONG TERM....DG 
MARINE.......RBP

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