FXUS63 KDTX 071702
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1202 PM EST MON DEC 7 2009

.AVIATION...

MID LEVEL MOISTURE (ABOVE 10 KFT) HAS BEEN STRIPPED AWAY FROM THE
AREA...WITH QUESTIONABLE LINGERING LOW LEVEL MOISTURE. THIS MAKES
FOR A TOUGH FORECAST THROUGH TONIGHT AS SURFACE RIDGE BUILDS INTO
THE AREA (LOWERING INVERSION)...WITH LOW CLOUDS IN QUESTION UNDER
LIGHT WESTERLY FLOW. HAVE GONE A BIT MORE OPTIMISTIC WITH THE
CLOUD COVER (MOSTLY VFR CEILINGS THIS AFTERNOON) WITH SKIES PARTLY
CLOUDY AT TIMES. DO THINK THERE COULD BE A COUPLE HOUR PERIOD OF
MVFR CEILINGS THIS EVENING AS WHAT EVER IS LEFT OF THE FRONT OVER
NORTHERN LOWER MICHIGAN FINALLY SWINGS SOUTHEAST AND DISSIPATES.
ASSUMING WE DO PARTIALLY CLEAR OUT TONIGHT...WILL LOOK FOR
INCREASING/THICKENING/LOWERING CLOUDS TOMORROW AHEAD OF A NEXT
MAJOR STORM SYSTEM. WILL ALSO NEED TO BE LEARY OF LOW STRATUS
DEVELOPMENT TOMORROW MORNING OFF LAKE ERIE AS LOW LEVEL SOUTHEAST
WINDS BEGIN TO INCREASE.

&&

.PREV DISCUSSION...ISSUED 434 AM EST MON DEC 7 2009 

SHORT TERM...TODAY

MAIN CONCERN TODAY IS HOW MUCH SNOW THIS WEAK SYSTEM CAN GRIND OUT 
AS IT MOVES THROUGH THE CENTRAL GREAT LAKES. THE EXTREME NORTHERN 
PORTION OF THE CWA...INCLUDING MIDLAND/BAY/HURON COUNTIES...WILL BE 
IN THE VICINITY OF A STALLED FRONTAL BOUNDARY AND BETTER MOISTURE 
SHOWN BY THE KAPX 00Z RAOB SOUNDING. IN ADDITION...A STRUNG OUT 
SHORTWAVE MOVING THROUGH THE SOUTHERN GREAT LAKES WILL LIFT NORTH 
PROVIDING ADDITIONAL LIFT DURING THE AFTERNOON HOURS.  THIS 
COMBINATION OF SURFACE CONVERGENCE...MID LEVEL FORCING AND BETTER 
MOISTURE SHOULD LEAD TO AROUND AN INCH OF ACCUMULATION DURING THE 
DAY TODAY.

SOUTH OF THIS BOUNDARY GRINDING OUT ANY SNOW WILL BE DIFFICULT AS  
THE KDTX 00Z RAOB SOUNDING SHOWS QUITE A BIT OF DRY AIR ABOVE AND 
BELOW 800 MB. WHILE THE MODELS SHOW SOME MEAGER ISENTROPIC LIFT THIS 
MORNING WITH MIXING RATIOS OF 1.25 TO 1.75 G/KG ON THE 285K SURFACE 
ALONG WITH A SHORTWAVE PASSING THROUGH THE SOUTHERN GREAT 
LAKES...MUCH OF THIS LIFT AND ASSOCIATED MOISTURE WILL BE SPENT 
SATURATING THE LOWER LAYERS. THEREFORE ONLY FLURRIES AND SCATTERED 
LIGHT SNOW SHOWERS ARE EXPECTED FURTHER SOUTH WITH A DUSTING OF SNOW 
BEING THE HIGHEST AMOUNT THIS SYSTEM CAN GRIND OUT SOUTH OF THE 
FRONTAL BOUNDARY TODAY.

CURRENT TEMPERATURES ARE CLOSE TO MOS VALUES AND A FEW DEGREES 
COLDER THAN YESTERDAY. THE SLIGHTLY COOLER TEMPERATURES ARE EXPECTED 
GIVEN THE AMOUNT OF CLOUD COVER HEADED FOR SOUTHEAST MICHIGAN AND 
THE ADVECTION OF SLIGHTLY COOLER AIR FROM THE NORTHWEST TODAY.

LONG TERM...TONIGHT THROUGH SUNDAY

SURFACE HIGH PRESSURE BUILDING INTO LOWER MICHIGAN WILL PROVIDE 
SUBSIDENCE AND DRY WEATHER OVERNIGHT...ASIDE FROM AN ISOLATED LIGHT 
SNOW SHOWER THAT COULD LINGER OVER THE THUMB DURING THE EVENING. 
QUESTION FOR THE OVERNIGHT PERIOD WILL BE WHETHER STRATUS 
LINGERS/DEVELOPS OVERNIGHT. GFS/NAM FORECAST SOUNDINGS DO NOT LOOK 
TOO IMPRESSIVE WITH INVERSIONS BUILDING TO TRAP MOISTURE...AND WILL 
DECREASE SKY COVER TO PARTLY CLOUDY BY MIDNIGHT BEFORE SKIES GO 
MOSTLY CLOUDY ONCE AGAIN AS HIGH/MID LEVEL MOISTURE INCREASES OVER 
SOUTHERN LOWER MICHIGAN LATE. 

MAIN STORY IN THE FORECAST CONTINUES TO CENTER AROUND HOW A STRONG 
LOW PRESSURE SYSTEM WILL AFFECT SOUTHEAST MICHIGAN DURING THE 
MIDWEEK PERIOD. 00Z MODELS HAVE ARRIVED WITH A STRONGER CONSENSUS 
THAN PREVIOUSLY DISPLAYED...AND THIS TRACK LINES UP FAIRLY CLOSE TO 
PREVIOUS FORECAST THINKING SO OVERALL CHANGES TO THE FORECAST WERE 
RELATIVELY SMALL. THE CENTER OF THE LOW IS CURRENTLY EXPECTED TO 
TRACK ALONG A LINE FROM CHICAGO UP THROUGH SAGINAW BAY...ALLOWING 
SOME WARM AIR TO PENETRATE UP INTO SOUTHEAST MICHIGAN. HOW FAR NORTH 
THE WARM AIR SURGES IS STILL A LITTLE UNCERTAIN...AND FOR THIS 
REASON HAVE OPTED TO NOT ISSUE A 4TH-5TH PERIOD WATCH (BARELY IN THE 
WINDOW) FOR BAY, MIDLAND, AND SAGINAW COUNTIES...WHICH STAND THE 
BEST CHANCE OF ALL PRECIPITATION FALLING AS SNOW WITH THE CURRENT 
FORECAST TRACK. ASIDE FROM JUST STARTING TO FEEL COMFORTABLE WITH 
THE MODEL TRACK...NAM AND WRF-HEMI CONTINUE TO TAKE THE TRACK NORTH 
OF THE CURRENT FORECAST AND THEREFORE HAVE WARMER THERMAL PROFILES. 
NAM IS ALSO BEST ALIGNED WITH THE MODEL CONSENSUS FROM MODEL RUNS 
LAST NIGHT...THOUGH IT IS NOT PREFERRED.

UPPER TROUGH OVER THE PACNW COAST WILL SWING DOWN INTO THE SOUTHWEST 
U.S. BEFORE RACING IN STRONG WESTERLY FLOW TOWARDS THE GREAT LAKES. 
00Z GFS/NAM/GEM/EURO HAVE ALL TRENDED FASTER WITH THE UPPER WAVE AS 
IT PROGRESSES ACROSS THE CENTRAL PLAINS...AND AS A RESULT ARE NOW 
FASTER WITH LIFTING THE PRECIPITATION SHIELD INTO LOWER MICHIGAN. 
HAVE ADDED LOW POPS TO THE LATE TUESDAY AFTERNOON PERIOD TO COVER 
THIS SCENARIO MODELS SHOW FAIRLY GOOD ISENTROPIC ASCENT BEGINNING TO 
OCCUR AFTER 21Z. ALTHOUGH TEMPERATURES WILL BE NEAR TO JUST SLIGHTLY 
BELOW FREEZING AT THE ONSET OF PRECIPITATION...EVAPORATIVE COOLING 
PROCESSES SHOULD TAKE OVER VERY QUICKLY AND ALLOW THIS PRECIPITATION 
TO FALL AS SNOW BY THE TIME SUB-CLOUD LAYER MOISTENS. SHOWERS SHOULD 
BE VERY LIGHT IN INTENSITY...WITH LITTLE TO NO SNOW ACCUMULATION.

MAIN AREA OF PRECIPITATION WILL BEGIN TO SPREAD OVERHEAD TUESDAY 
EVENING AS THE LOW LIFTS OUT OF THE CENTRAL PLAINS AND TOWARDS THE 
CHICAGO AREA. AS THIS OCCURS...WARMER AIR WILL BEGIN TO BE DRAWN UP 
INTO SOUTHEAST MICHIGAN AND BEGIN TO CHANGE THE SNOW OVER TO RAIN. 
FORECAST SOUNDINGS FROM THE GFS SUPPORT A NORTH TO SOUTH CHANGEOVER 
OCCURRING AS FAR NORTH AS FNT AFTER 1 AM...WITH SOME SLEET EVEN 
POSSIBLE SOUTH OF M-59 AS WARMER AIR ALOFT BRUSHES THE AREA. 
ALTHOUGH LIGHT PRECIPITATION SHOULD START IN THE EVENING...THE 
HEAVIEST ACCUMULATIONS OF SNOW/RAIN ARE NOT EXPECTED TO BEGIN UNTIL 
AFTER 6Z/1AM...COINCIDING WITH THE ARRIVAL OF A COUPLED JET 
STRUCTURE AND BETTER DEFORMATION AND FGEN FORCING. MOISTURE WILL NOT 
BE A PROBLEM...WITH SPECIFIC HUMIDIFIES REACHING 3-4 G/KG BELOW 
700MB. SNOW ACCUMULATIONS ARE DEPENDENT ON HOW FAR NORTH THE WARM 
AIR SURGES AS WELL AS HOW QUICKLY THIS OCCURS...WITH CURRENT 
FORECAST BETWEEN 1-2 INCHES NEAR THE OHIO BORDER AND AROUND 5 INCHES 
ACROSS THE TRI-CITIES.

THE LOW SHOULD TRACK UP INTO SAGINAW BAY BY 18Z...DRAWING WARMER AIR 
UP INTO THE AREA SOUTH OF THERE AND PULLING MORE COLD AIR DOWN INTO 
THE SYSTEM NORTH OF THERE. ALL FORECAST SOUNDINGS SUPPORT A 
CHANGE TO ALL RAIN FROM FLINT SOUTHWARD...AND AT LEAST MIX IN 
SOME RAIN AS FAR NORTH AS BAY CITY...MAKING ADDITIONAL SNOW 
ACCUMULATIONS ON WEDNESDAY PROBLEMATIC TO FORECAST. TOP SNOW AMOUNTS 
WOULD BE AN ADDITIONAL 4 INCHES FOR THE TRI-CITIES...INCLUDING 
AMOUNTS THEY COULD SEE IN THE TROWAL. POWERFUL COLD FRONT PUSHING 
ACROSS THE REGION ON THE BACKSIDE OF THE SYSTEM WILL BRING A QUICK 
CHANGE BACK TO ALL SNOW LATE WEDNESDAY AFTERNOON/EVENING AS WRAP 
AROUND MOISTURE AND LAKE EFFECT PROCESSES RESIDE OVER THE AREA. THE 
PASSAGE OF THIS FRONT WILL KICK UP SOME VERY GUSTY WINDS...WITH 
SOUNDINGS SUGGESTING GUSTS COULD REACH 45 KNOTS WEDNESDAY NIGHT AND 
THURSDAY. STRONG COLD AIR ADVECTION WILL CONTINUE ON 
THURSDAY...LIMITING HIGHS INTO THE 20S.

LAKE EFFECT SNOW SHOWERS WILL CONTINUE ACROSS THE AREA ON WEDNESDAY 
NIGHT AND THURSDAY...AND GIVEN THE DEGREE OF COLD AIR AND LAKE 
INDUCED CAPE (TOPPING 1000 J/KG) AND FAST FLOW ACROSS LAKE 
MICHIGAN...WOULD NOT BE SURPRISED TO SEE ADDITIONAL SNOW 
ACCUMULATIONS. COLD AIR WILL REMAIN IN PLACE OVER THE REGION THROUGH 
THE WEEKEND...WITH HIGHS ONLY IN THE UPPER 20S TO LOW 30S.

MARINE...

A WEAK LOW PRESSURE SYSTEM MOVING THROUGH THE CENTRAL GREAT LAKES 
WILL CAUSE GUSTY WINDS AS IT PASSES THROUGH THIS AFTERNOON AND 
TONIGHT. HOWEVER WINDS AND WAVES WILL REMAIN BELOW SMALL CRAFT 
ADVISORY CRITERIA DURING THIS PERIOD. 

A VERY STRONG LOW PRESSURE SYSTEM WILL TRACK THROUGH THE CENTRAL 
GREAT LAKES ON WEDNESDAY. THIS STORM SYSTEM WILL BRING A PROLONGED 
PERIOD OF STRONG WINDS TO THE GREAT LAKES FROM TUESDAY NIGHT THROUGH 
FRIDAY. A BRIEF PERIOD (6 HOURS OR LESS) OF EASTERLY GALES MAY 
DEVELOP OVER THE OPEN WATERS OF LAKE HURON AHEAD OF THE SYSTEM 
TUESDAY NIGHT AND EARLY WEDNESDAY. A POWERFUL COLD FRONT WILL THEN 
SWEEP ACROSS THE CENTRAL GREAT LAKES WEDNESDAY AFTERNOON AND 
EVENING...WITH WESTERLY GALES LOOKING LIKELY ACROSS ALL MARINE 
WATERS WEDNESDAY NIGHT AND THURSDAY...AS THE LOW DEEPENS TO 28.80 
INCHES OR LOWER. THERE IS ALSO A POSSIBILITY TO SEE GUSTS REACH 
STORM FORCE ACROSS THE OPEN WATERS OF LAKE HURON WEDNESDAY NIGHT AND 
THURSDAY. WINDS WILL BE SLOW TO DECREASE AS WE HEAD INTO FRIDAY...AS 
THE ARCTIC AIRMASS SPILLING OVER THE WARMER WATERS LEADS TO VERY 
UNSTABLE LOW LEVEL PROFILE...ALLOWING WAVE GROWTHS IN EXCESS 10 
FEET. LAKE EFFECT SNOW SQUALLS WILL ALSO BE POSSIBLE BEHIND THE 
SYSTEM...ESPECIALLY FROM LATE WEDNESDAY NIGHT THROUGH THURSDAY AS 
EXTREMELY COLD AIR RIDES OVER THE WARM LAKE WATERS.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

AVIATION.....SF
SHORT TERM...KURIMSKI
LONG TERM....HLO
MARINE.......KURIMSKI/HLO

YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).