391 
FXUS63 KDTX 031741
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
141 PM EDT FRI SEP 3 2010


.AVIATION...

DEEP LAYER MIXING BEHIND A STRONG COLD FRONT WILL ALLOW FOR AN
INCREASE IN WESTERLY WINDS THIS AFTERNOON...WITH GUSTS AROUND 30
KNOTS. THESE WINDS WILL SUBSIDE SOMEWHAT DURING THE EVENING...BUT
STILL REMAIN GUSTY OVERNIGHT AS A SECOND STRONG COLD FRONT DROPS
ACROSS SOUTHEAST MICHIGAN. MEANWHILE...MOISTURE FEED OFF LAKE MICHIGAN
WILL CONTINUE TO GENERATE SCT-BKN SKY COVER...BUT CEILINGS SHOULD
REMAIN VFR THROUGH THE EARLY EVENING. AN ADDITIONAL POOL OF LOW-
LEVEL MOISTURE WILL ARRIVE WITH THE SECOND COLD FRONT THIS
EVENING. FORECAST MODELS AND UPSTREAM OBSERVATIONS FROM WISCONSIN
SUPPORT CEILINGS DROPPING TO MVFR AT ALL TAF SITES ACROSS LOWER
MICHIGAN BY LATE EVENING...THEN LASTING INTO MID-MORNING ON SATURDAY
BEFORE MIXING ALLOWS CEILINGS TO LIFT TO VFR. SHOWER POTENTIAL
ACROSS MICHIGAN TONIGHT LOOKS GREATEST IN AREAS FAVORABLE FOR LAKE
EFFECT...ALTHOUGH THERE WILL BE AT LEAST A LOW CHANCE EVERYWHERE.
HAVE NOT INCLUDED SHOWERS IN THE 18Z TAF PACKAGE HOWEVER SINCE THE
CHANCES ARE QUITE LOW. WINDS WILL BE VERY GUSTY ONCE AGAIN
TOMORROW...WITH WESTERLY GUSTS BETWEEN 30 AND 35 KNOTS DEVELOPING
IN THE EARLY AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 342 AM EDT FRI SEP 3 2010 

SHORT TERM...TODAY

AREA OF SUBSTANTIAL UPPER HEIGHT FALLS RAPIDLY WORKING EAST TOWARD 
THE GREAT LAKES EARLY THIS MORNING...LEAD BY A STRONG SHORTWAVE 
PIVOTING AROUND A DEEPENING LONGWAVE TROUGH OVER THE UPPER 
MISSISSIPPI VALLEY.  THE CORRESPONDING DEEPENING NORTHWEST FLOW 
WILL RESULT IN A PERIOD OF GOOD COLD AIR ADVECTION STARTING TODAY.  
THE ASSOCIATED INITIAL COLD FRONTAL BOUNDARY WILL SHIFT THROUGH 
SOUTHEAST MICHIGAN DURING THE MID-LATE MORNING HOURS.  ELONGATED 
AXIS OF HIGHER PRE-FRONTAL LOW-MID LEVEL THETA-E AIR IN THE PRESENCE 
OF INCREASING CONVERGENCE WILL CONTINUE TO SUPPORT SHOWERS/EMBEDDED 
THUNDER IN ADVANCE OF THE FRONT THIS MORNING...BEFORE THE RAPIDLY 
ADVANCING MID LEVEL DRY SLOT BRINGS A QUICK END TO ANY LINGERING 
SHOWERS FROM WEST TO EAST BY LATE MORNING.  

COLD AIR ADVECTION WILL THEN COMMENCE THROUGH THE REMAINDER OF THE 
DAY.  A PERIOD SUFFICENT POST-FRONTAL LOW TO MID LEVEL DRYING 
ACCOMPANIED BY SUBSIDENCE WILL ALLOW FOR AT LEAST PARTIAL SUN... 
HELPING TO COUNTER THE ADVECTIVE PROCESS.  THIS SUPPORTS HIGHS 
RANGING FROM AROUND 70F ACROSS THE SAGINAW VALLEY TO MID 70S OVER 
THE SOUTHEAST CORRIDOR /PORT HURON TO MONROE/.  A DEEP MIXED LAYER 
WILL EVOLVE AS LOW LEVEL LAPSE RATES STEEPEN INTO THE AFTERNOON.  
SOUNDINGS CONTINUE TO SUGGEST POTENTIAL GUSTS PEAKING AROUND 40 
MPH...OR REMAINING JUST BELOW ADVISORY LEVELS.

LONG TERM...

OUR FIRST GOOD SHOT OF AUTUMN LIKE WEATHER WILL ARRIVE FOR THE 
WEEKEND...BUT WILL BE SHORT LIVED AS TEMPERATURES QUICKLY WARM UP 
EARLY NEXT WEEK. 

UPPER LEVEL LOW/TROUGH NOW PUSHING INTO THE WESTERN GREAT 
LAKES...WILL CONTINUE TO AMPLIFY...LEADING TO FURTHER COOLING OF 
THE LOW/MID LEVELS...AS SURFACE LOW DEEPENS TO 993-995 MB OVER 
ONTARIO TODAY. THIS SYSTEM WILL ABSORB EARL OVER QUEBEC DURING THE 
WEEKEND...WITH HEIGHTS SLOWLY RISING OVER SOUTHERN LOWER MICHIGAN ON 
SUNDAY...WITH SHORTWAVE RIDGE MOVING OVERHEAD ON MONDAY...PER 00Z 
GFS/12Z EUROPEAN. 

TONIGHT WILL BE WINDY...BUT BASED ON THE 00Z NAM...NOT WORTHY OF A 
WIND ADVISORY AS 925-850 MB WINDS ARE PROGGED TO BE AROUND 35 KNOTS.
EVEN THE STRONGER GFS IS ONLY INDICATING ABOUT A 9 MB DIFFERENCE 
ACROSS THE RISE/FALL 6 HR PRESSURE COUPLET WHICH TRACKS ACROSS.  

LOW LEVEL COLD ADVECTION ON SATURDAY...BUT EXPECTING CONSIDERABLE 
MODERATION TO THE AIRMASS WITH LAKE MICHIGAN WATER TEMPERATURES 
STILL IN THE LOWER 70S. MAXES IN THE LOW/MID 60S IS A NICE BLEND 
BETWEEN THE WARMER NAM/COLDER GFS...850 MB TEMPS AROUND 4 C. 
THE NAM SOUNDINGS INDICATING CAPES UP TO 100 J/KG WITH THE STEEP LOW 
LEVEL LAPSE RATES...AND DIURNAL SCATTER LIGHT SHOWERS ARE 
LIKELY...ESPECIALLY ACROSS THE THUMB REGION WITH ENHANCEMENT OFF 
SAGINAW BAY. 

MID 40S IS THE COLDEST I CAN SEE FOR SATURDAY NIGHT...AS SOME CLOUD 
COVER IS EXPECTED TO PERSIST. WINDS MAY NOT TOTALLY DIE OFF EITHER. 

UPPER LEVEL NORTHWEST CONFLUENT FLOW AND LOW LEVEL ANTI-CYCLONIC 
FLOW ON SUNDAY SHOULD LEAD TO MORE SUNSHINE...WITH TEMPERATURES 
RESPONDING INTO THE LOWER 70S...IN LINE WITH LATEST GUIDANCE. 

THE 00Z EUROPEAN/GFS ARE REMAINING CONSISTENT INDICATING A STRONG 
LOW TRACKING NORTHEAST THROUGH MINNESOTA EARLY NEXT WEEK...LIFTING 
A WARM FRONT THROUGH SOUTHERN LOWER MICHIGAN. WITH 850 MB TEMPS 
RISING INTO THE UPPER TEENS...AND SOUTHWEST LOW LEVEL FLOW 
DEVELOPING...TEMPERATURES INTO THE 80S LOOKS REASONABLE...ALTHOUGH 
THE TIMING OF THE THERMAL RIDGE LOOKS TO BE MONDAY NIGHT...OR ELSE 
WOULD HAVE BUMPED UP INHERITED TEMPERATURES FURTHER. IF THE COLD 
FRONT IS ABLE TO SLOW DOWN...MAY MAKE A RUN AT 90 DEGREES ON 
TUESDAY. WITH 700 MB TEMPS AROUND 10 C (CAP) AND A VERY NARROW 
RIBBON OF MOISTURE ASSOCIATED WITH THE FRONT...NOT READY TO 
INTRODUCE POPS YET FOR TUESDAY.

MARINE...

A STRENGTHENING LOW PRESSURE SYSTEM LIFTING ACROSS SOUTHERN CANADA 
WILL BRING AN INITIAL COLD FRONT THROUGH THE REGION THIS MORNING.  
THIS COMBINED WITH A DEEPENING MIXED LAYER WILL RESULT IN WEST TO 
SOUTHWEST GUSTS OF 20 TO 30 KNOTS BY THIS AFTERNOON.  THE POTENTIAL 
EXISTS FOR A PERIOD OF GALE FORCE GUSTS OVER THE LAKE HURON 
NEARSHORES BY LATE AFTERNOON.  A SECONDARY COLD FRONT WILL LEAD IN 
A STRONGER SURGE OF COOLER AIR BY TONIGHT.  THE INCREASING 
INSTABILITY ACROSS THE LAKE WILL RESULT IN AN EXTENDED PERIOD OF 
GALES OVER LAKE HURON THROUGH SATURDAY EVENING.  SMALL CRAFT 
ADVISORY CONDITIONS WILL EXIST OVER LAKES ST CLAIR AND ERIE THROUGH 
THIS TIME.  THE DEGREE OF INSTABILITY MAY ALSO LEAD TO SOME 
THUNDERSTORM DEVELOPMENT. WINDS AND WAVES WILL BEGIN TO DEGREASE ON 
SUNDAY AND CONTINUE INTO MONDAY AS WEAK HIGH PRESSURE ADVANCES INTO 

&&

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

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT 
     HURON INCLUDING SAGINAW BAY...UNTIL 4 PM FRIDAY.

     GALE WARNING...NEARSHORE WATERS FROM PORT AUSTIN TO PORT HURON 
     INCLUDING SAGINAW BAY...UNTIL 10 PM SATURDAY.

     GALE WARNING...LHZ361-LHZ362-LHZ363-LHZ462-LHZ463-LHZ464...FROM 8 
     PM FRIDAY TO 5 AM SUNDAY.

LAKE ST CLAIR...
     SMALL CRAFT ADVISORY...UNTIL 10 PM SATURDAY.

MI WATERS OF LAKE ERIE...
     SMALL CRAFT ADVISORY...UNTIL 10 PM SATURDAY.

&&

$$

AVIATION.....HLO
SHORT TERM...MR
LONG TERM....SF
MARINE.......MR


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