001  
FXUS63 KDTX 201123  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
723 AM EDT SUN AUG 20 2017  
   
AVIATION
 
 
HIGH PRESSURE WILL BRING VFR CONDITIONS THROUGHOUT THE FORECAST  
PERIOD. LIGHT WINDS AND GOOD RADIATIONAL COOLING IS GENERATING  
AREAS OF SHALLOW FOG WHICH WILL QUICKLY DISSIPATE AFTER SUNRISE.  
LIGHT/VARIABLE WINDS WILL BECOME SOUTHWEST UNDER 10 KNOTS ON THE  
BACKSIDE OF THIS HIGH BY MID/LATE MORNING WITH JUST A FEW DIURNAL  
CUMULUS POSSIBLE WITHIN A RATHER DRY AIRMASS. WEAK SURFACE FLOW AND  
DAYTIME HEATING COULD BRING A LAKE BREEZE UP TO OR THROUGH DTW LATE  
AFTERNOON/EVENING BACKING WINDS MORE SOUTH SOUTHEAST BUT WOULD REMAIN  
UNDER 10 KNOTS. LIGHT SOUTHWEST FLOW TONIGHT WILL BRING INCREASING  
DEWPOINTS. PATCHES OF HIGH CLOUDS FROM CONVECTION IN THE MIDWEST MAY  
MAKE IT OVER THE TAF SITES, HOWEVER, THERE SHOULD STILL BE ENOUGH  
RADIATIONAL COOLING TO PRODUCE A BIT MORE WIDESPREAD FOG IN THE 4-6  
MILE RANGE TOWARDS SUNRISE MONDAY.  
 
//DTW THRESHOLD PROBABILITIES...  
 
* NONE.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 400 AM EDT SUN AUG 20 2017  
 
DISCUSSION...  
 
HIGH PRESSURE COVERING MUCH OF THE COUNTRY EAST OF THE MISSISSIPPI  
DURING THE MORNING WILL BECOME CENTERED MORE ALONG THE ATLANTIC  
COAST DURING THE AFTERNOON. THIS WILL ENSURE A SUNNY START TO THE  
DAY ACROSS SE MICHIGAN AFTER SOME PATCHY AND SHALLOW FOG AROUND  
SUNRISE. LIGHT AND VARIABLE WIND WILL THEN TAKE ON A MORE SOUTHERLY  
COMPONENT AND HELP BOOST TEMPERATURES INTO THE MID 80S MOST  
LOCATIONS. MODEL SOUNDINGS INDICATE THE BOUNDARY LAYER WILL BE TOO  
DRY FOR ANYTHING MORE THAN A FEW CUMULUS BUT THICKENING CIRRUS IS  
EXPECTED LATE IN THE DAY AS MCS DEBRIS DRIFTS EASTWARD FROM THE  
PLAINS. THESE CLOUDS ARE TIMED TOO LATE TO HAVE AN IMPACT ON  
AFTERNOON TEMPERATURES AND THEN WILL THIN DURING THE EVENING AND  
ALLOW SOME RADIATIONAL COOLING TONIGHT. GUIDANCE LOWS IN THE LOWER  
TO MID 60S LOOK GOOD.  
 
LARGER SCALE WEATHER FEATURES IN THE PLAINS TODAY WILL HAVE AN  
INCREASING INFLUENCE ON GREAT LAKES CONDITIONS MONDAY AND ESPECIALLY  
BY TUESDAY. MOSTLY ZONAL FLOW ALOFT THROUGH THE NORTHERN TIER OF  
STATES IS PRODUCING A CLASSIC LEE SIDE SURFACE TROUGH WHILE THE  
UPPER LEVEL WAVE OVER CENTRAL CANADA IS SUPPORTING A COLD FRONT AS  
FAR SOUTH AS THE DAKOTAS. THESE FEATURES INTERSECT A WARM FRONT OVER  
THE MISSOURI VALLEY THAT IS THE FOCUS FOR LOW LEVEL JET FORCED MCS  
ACTIVITY. ONGOING NOCTURNAL CONVECTION DURING THE EARLY MORNING IS  
EXPECTED TO FOLLOW A STANDARD DAYTIME WEAKENING TREND WHILE ZONAL  
FLOW GUIDES CLOUD REMNANTS AND ANY RESIDUAL MCV INTO THE SOUTHERN  
GREAT LAKES. THE LATEST MODEL SOLUTIONS THEN LOOK REASONABLE WITH  
THE SLOW EASTWARD MIGRATION OF THE SURFACE FEATURES INTO THE MIDWEST  
TONIGHT. SOME SURFACE BASED CONVECTION IN SHOWN OVER THE NORTHERN  
GREAT LAKES THIS AFTERNOON AND EVENING WHILE REMAINING CAPPED  
FARTHER SOUTH TOWARD IOWA AND ILLINOIS. THIS WILL SET UP THE GENESIS  
REGION FOR ROUND 2 OF LOW LEVEL JET FORCED MCS ACTIVITY ON THE EDGE  
OF THE 850-700 MB CAP CENTERED ON IOWA, MUCH FARTHER EAST THAN  
ACTIVITY OCCURRING EARLY THIS MORNING. THE STRONGEST CONVECTION  
SHOULD DIVE SOUTHEAST ALONG THE INSTABILITY GRADIENT FROM THERE  
WHILE SUBSTANTIAL CLOUD DEBRIS AND EVEN SOME MCV SUPPORTED SHOWERS  
COULD MAKE IT INTO LOWER MICHIGAN BY LATE MONDAY MORNING INTO  
AFTERNOON.  
 
A NEW ROUND OF SHORT WAVE INDUCED HEIGHT FALLS IS ALSO PROJECTED TO  
DEVELOP OVER CENTRAL CANADA MONDAY INTO MONDAY NIGHT WHICH WILL LEAD  
TO A PAUSE IN THE EASTWARD PROGRESS OF THE COLD FRONT. THE CANADIAN  
SHORT WAVE WILL PRODUCE A SURFACE WAVE ALONG THE FRONT ABOUT AT THE  
SAME TIME MID LEVEL MONSOONAL MOISTURE IS DRAWN INTO THE WESTERLIES  
FROM THE SOUTHWEST STATES. A NEW ROUND OF DEEP WARM/MOIST ADVECTION  
WILL PRODUCE ADDITIONAL MCS DEVELOPMENT OVER THE PLAINS AND MIDWEST  
AS THE LOW PRESSURE SYSTEM MATURES. THE DEEPENING UPPER WAVE WILL  
PROVIDE STRONG FORCING AND A STRONG WIND PROFILE WHILE THE  
INSTABILITY AXIS/THETA-E RIDGE SPREADS NORTHWARD OVER THE GREAT  
LAKES AHEAD OF THE FRONT. THESE LARGE SCALE FEATURES WILL SUSTAIN  
ORGANIZED CONVECTION THROUGH LOWER MICHIGAN LATE MONDAY NIGHT  
THROUGH TUESDAY BEFORE THE FRONT EXITS EASTWARD BY TUESDAY EVENING.  
 
AFTER THE TUESDAY FRONTAL PASSAGE, GLOBAL MODEL SOLUTIONS MAINTAIN A  
SHARPER UPPER LEVEL TROUGH, AND EVEN SOME SIGNS OF A CLOSED LOW,  
OVER EASTERN CANADA BY WEDNESDAY. THIS WILL OPEN THE DOOR FOR  
STRONGER HIGH PRESSURE TO DEVELOP OVER CENTRAL CANADA AND SPREAD  
COLDER AIR INTO THE GREAT LAKES WEDNESDAY INTO THURSDAY. THE LATEST  
ROUND OF GUIDANCE TEMPERATURES NOW OFFER HIGHS IN THE UPPER 60S IN  
THE THUMB REGION BY THURSDAY WHICH MATCH UP BETTER WITH 850 MB  
TEMPERATURES IN THE 5-10C RANGE. MODIFYING HIGH PRESSURE THEN HOLDS  
DURING THE SECOND HALF OF THE WEEK AND INTO NEXT WEEKEND.  
 
MARINE...  
HIGH PRESSURE CENTERED OVER MICHIGAN WILL GRADUALLY SLIDE TO THE  
EAST TODAY MAINTAINING A LIGHT MAINLY SOUTHWESTERLY FLOW THROUGH  
MONDAY. INCREASING MOISTURE AND A SLOWLY ADVANCING COLD FRONT WILL  
BRING SHOWERS AND THUNDERSTORMS LATE TONIGHT ACROSS NORTHERN LAKE  
HURON. THIS CHANCE WILL SPREAD SOUTH DURING THE DAY MONDAY AND  
CONTINUE UNTIL THE STRONG COLD FRONT SWEEPS THROUGH TUESDAY  
AFTERNOON. WINDS WILL THEN BECOME STRONG FROM THE NORTHWEST AND  
CONTINUE THROUGH THE END OF THE WEEK.  
 

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

 
 

 
 
AVIATION.....DRC  
DISCUSSION...BT  
MARINE.......DRC  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT.  
 
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