332  
FXUS63 KDTX 080357  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
1157 PM EDT TUE JUL 7 2015  
 
   
AVIATION
 
 
MVFR STRATUS WILL CONTINUE TO GRADUALLY ERODE FROM NORTH TO SOUTH  
ACROSS THE AREA AS DRIER LOW LEVEL AIR WORKS IN WITH BUILDING HIGH  
PRESSURE. EXPECT FEW-SCT LOWER VFR DECK BY 08Z ACROSS ALL TERMINALS.  
THIS SHOULD REMAIN THE RULE THROUGH MUCH OF WEDNESDAY BEFORE LOWER  
CIGS TRY TO EXPAND BACK INTO AREA LATE IN THE FORECAST AS LOW  
PRESSURE LIFTS INTO THE OHIO VALLEY.  
 
FOR DTW...REMAINING MVFR/LOWER VFR BKN CIGS WILL TREND TO FEW-SCT  
AFTER 08Z WITH ANOTHER CHANCE OF MVFR CIGS AFTER 06Z WEDNESDAY  
NIGHT.  
 
//DTW THRESHOLD PROBABILITIES...  
 
* MEDIUM FOR CEILINGS LESS THAN 5000 FT THROUGH 08Z AND LOW FOR  
WEDNESDAY NIGHT.  
 

 
   
PREV DISCUSSION
 
ISSUED 339 PM EDT TUE JUL 7 2015  
 
SHORT TERM...THROUGH TONIGHT  
 
THE COLD FRONT IS CURRENTLY COMPLETING ITS PASSAGE ACROSS SE  
MI...CURRENTLY ALIGNED ALONG THE DETROIT RIVER. SOME ENHANCED  
MOISTURE BEHIND THE FRONT IS LEADING TO SOME LIGHT RAIN AND  
DRIZZLE...BUT THAT WILL NOT LAST LONG AS DRY AIR QUICKLY SURGES  
SOUTHEASTWARD ACROSS THE STATE. DEWPOINTS ACROSS NORTHERN MI AREA  
ALREADY DOWN BELOW 50 DEGREES WITH MID 50S ACROSS MID MI. MODELS  
ADVERTISE THE FRONT TO SLOWLY TAKE ON A MORE E/W ORIENTATION ACROSS  
THE NORTHERN OHIO VALLEY OVERNIGHT AS AN AREA OF SFC HIGH PRESSURE  
BUILDS IN ACROSS THE GREAT LAKES. THE RESULT WILL BE A DECENT  
DEWPOINT GRADIENT ACROSS THE AREA RANGING FROM THE UPPER 40S ACROSS  
THE SAGINAW VALLEY UP TO THE MID 50S NEAR THE OHIO BORDER. THIS WILL  
IN TURN SET THE LIMIT TO THE COOLING POTENTIAL OVERNIGHT EVEN AS  
SKIES CLEAR UNDER A SHORTWAVE RIDGE SLIDING OVERHEAD AND SFC HIGH  
PRESSURE IN PLACE...AND 925MB TEMPS FALL TO 12C. THE BIG QUESTION IS  
HOW MUCH ARE THE MODELS OVER DOING THE BL MOISTURE BEHIND THE FRONT?  
WILL LEAN TO A DRIER FORECAST WITH MOSTLY CLEAR SKIES AS THE VISIBLE  
SATELLITE IS ALREADY SHOWING THE CU FIELD ERODING OVER THE UP AND  
NORTHERN MI.  
 
LONG TERM...  
 
EXPANSIVE HIGH PRESSURE CURRENTLY OVER THE NORTHERN PLAINS WILL TAKE  
OVER DURING THE DAY ON WEDNESDAY AS IT MOVES EAST INTO THE GREAT  
LAKES REGION. THIS HIGH WILL BRING A DAY OF DRIER CONDITIONS BEFORE  
THE NEXT LOW ENTERS BACK INTO THE PICTURE. LOW PRESSURE WILL BE IN  
THE PROCESS OF MOVING IN FROM THE SOUTHWEST LATE WEDNESDAY NIGHT  
BRINGING ANOTHER CHANCE FOR RAIN. BETTER CHANCE FOR RAIN WILL OCCUR  
ACROSS SOUTHERN AREAS OF THE CWA...ESPECIALLY AREAS CLOSER TO THE  
OHIO BORDER AS THE LOW SKIRTS ALONG NORTHERN OHIO AND LAKE ERIE.  
THIS CORRELATES TO WHERE THE BETTER INSTABILITY WILL BE AS THE SYSTEM  
QUICKLY MOVES ACROSS AND OFF TO THE EAST. CURRENT TIMING OF THE  
HEAVIER RAIN LOOKS TO BE THURSDAY MORNING...BUT WITH TIMING ISSUES  
IN THE VARIOUS MODELS THIS WILL BE NARROWED DOWN WITH LATER FORECAST  
ISSUANCES. THIS SYSTEM IS EXPECTED TO BRING AREAS OF HEAVIER RAIN  
AS THE LATEST SOUNDINGS ARE ADVERTISING PWAT VALUES CLIMBING INTO  
THE 1.5 TO 2 INCH RANGE. RAIN THEN DIMINISHES BY LATE THURSDAY  
AFTERNOON AS HIGH PRESSURE BUILDS BACK IN OVER THE AREA LASTING  
THROUGH THE OVERNIGHT HOURS.  
 
FRIDAY THROUGH MONDAY...STRONG UPPER RIDGE OVER THE SOUTHEASTERN US  
WILL RETROGRADE TO THE WEST. THE RIDGE NEVER QUITE BUILDS ALL THE  
WAY INTO THE GREAT LAKES...LEAVING US ON THE ACTIVE OUTER FRINGES  
WITH PERIODIC DISTURBANCES ARGUING FOR SHOWER AND THUNDERSTORM  
CHANCES. DEEP-LAYER MOISTURE WILL INCREASE INTO THE WEEKEND AS WELL  
WITH PWATS AOA 1.5 INCHES FROM SATURDAY ONWARD. FORECAST TEMPS LOOK  
TO BE NEAR TO SLIGHTLY ABOVE NORMAL.  
 
MARINE...  
 
WINDY CONDITIONS BEHIND THE PASSING COLD FRONT WILL CONTINUE TO  
DIMINISH THROUGH THE EVENING AS HIGH PRESSURE BUILDS IN OVERNIGHT  
AND INTO WEDNESDAY. SMALL CRAFT ADVISORIES REMAIN IN EFFECT THOUGH  
EARLY TOMORROW MORNING FOR THE NEARSHORE WATERS OF SOUTHERN LAKE  
HURON. HIGH PRESSURE...AVERAGING 30.10 INCHES...WILL HOLD THROUGH  
THE DAY AND INTO THE EVENING ON WEDNESDAY BEFORE A WEAK LOW PRESSURE  
SYSTEM MOVES ACROSS THE SOUTHERN GREAT LAKES. THIS LOW WILL  
INCREASE EASTERLY/NORTHEASTERLY FLOW ACROSS LAKE ST CLAIR AND LAKE  
ERIE BEFORE WINDS BECOME LIGHT FOR THE REMAINDER OF THE WEEK.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 6 AM EDT WEDNESDAY FOR LHZ441>443.  
 
LAKE ST CLAIR...NONE.  
MICHIGAN WATERS OF LAKE ERIE...NONE.  

 
 

 
 
AVIATION.....DG  
SHORT TERM...DRK  
LONG TERM....SS/DT  
MARINE.......SS  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).  
 
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