260  
FXUS63 KDTX 091942  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
342 PM EDT SAT AUG 9 2025  
   
KEY MESSAGES
 
 
- HOT AND MUGGY WEATHER THROUGH THE WEEKEND WITH HEAT INDEX WELL  
INTO THE 90S TODAY THROUGH MONDAY.  
 
- DRY OVER THE WEEKEND, THEN SCATTERED SHOWERS AND THUNDERSTORMS  
RETURN EARLY NEXT WEEK.  
 

 
   
DISCUSSION
 
 
A RIDGE CONTINUES TO STRENGTHEN OVER SE MI AND THE EASTERN GREAT  
LAKES TODAY IN RESPONSE TO A BROAD CLOSED UPPER LOW TRACKING ACROSS  
SOUTHERN MANITOBA. THE RIDGE IS CHARACTERIZED BY 500MB GEOPOTENTIAL  
HEIGHTS OF AROUND 591 TO 593 DAM, NOTABLE EVEN BY EARLY AUGUST  
STANDARDS AS EXCEEDING THE 90TH PERCENTILE PER SPC SOUNDING  
CLIMATOLOGY. MID-LEVEL SOUTHWEST FLOW BENEATH THIS RIDGE SENDS 850MB  
TEMPS TO THE UPPER TEENS C TODAY WHERE THEY STAY PUT THROUGH THE  
REST OF THE WEEKEND AND INTO EARLY NEXT WEEK. AS THE UPPER LOW  
TRACKS FROM SOUTHERN MANITOBA TOWARD HUDSON BAY ON SUNDAY, THE  
ATTENDANT SURFACE COLD FRONT STALLS UPSTREAM FROM LAKE SUPERIOR  
TOWARD THE MID-MISSISSIPPI VALLEY, KEEPING CONVECTION WELL TO OUR  
WEST AND STABLE CONDITIONS IN PLACE LOCALLY AT LEAST THROUGH THE  
BULK OF SUNDAY.  
 
HEAT REMAINS THE MAIN SENSIBLE WEATHER TOPIC AS HIGHS TOP OUT IN THE  
LOWER 90S EACH DAY WITH DEW POINTS GENERALLY IN THE UPPER 60S TO  
AROUND 70. THIS TRANSLATES TO A DAILY MAX HEAT INDEX IN THE MID 90S,  
GENERALLY HIGHEST IN THE SAGINAW VALLEY WHERE SUBTLE DOWNSLOPING  
PLAYS A ROLE WITHIN THE LIGHT SOUTH TO SOUTHWEST WIND. 12Z HREF  
INDICATES LESS THAN A 20% PROBABILITY TO EXCEED APPARENT T OF 98 FOR  
A FEW HOURS EACH LATE AFTERNOON - SHY OF HEAT HEADLINE CRITERIA.  
 
LITTLE CHANGE IN THE SETUP THROUGH EARLY MONDAY AS THE UPPER MIDWEST  
TROUGH HOLDS THE RIDGING IN PLACE ACROSS THE LOWER GREAT LAKES. THE  
CAP WILL BE WEAKEST ACROSS THE SAGINAW VALLEY ON SUNDAY SO CAN'T  
RULE OUT A FEW LATE AFTERNOON SHOWERS OR STORMS. HOWEVER, THE BULK  
OF MID-LEVEL FORCING AND LOW-LEVEL TRIGGERS FOR CONVECTION WILL  
REMAIN DISPLACED TO THE WEST. BY MONDAY THE RIDGE BEGINS TO DEPART  
EAST AS SHORTWAVE ENERGY ROUNDS THE BASE OF THE TROUGH. THIS WEAKENS  
THE CAP FURTHER AND BRINGS SLIGHTLY HIGHER LIKELIHOOD FOR SCATTERED  
SHOWERS AND THUNDERSTORMS BY LATE IN THE DAY, WITH GUIDANCE SHOWING  
A PRE-FRONTAL TROUGH AS A POTENTIAL TRIGGERING MECHANISM. AGAIN, THE  
HIGHEST LIKELIHOOD WILL BE AROUND THE SAGINAW VALLEY. WITH BULK  
SHEAR OF LESS THAN 20 KT IN PLACE, THERE IS LITTLE POTENTIAL FOR  
SEVERE WEATHER BUT ANY STORMS THAT DO OCCUR WOULD BE RELATIVELY SLOW-  
MOVING AND PRODUCE LOCALIZED HEAVY RAINFALL GIVEN DEEP MOISTURE  
PROFILES AND PWAT APPROACHING 2 INCHES.  
 
THE STALLED FRONT SLOWLY INCHES EASTWARD INTO THE AREA ON TUESDAY  
WITH PRECEDING SOUTHWEST FLOW ADVECTING THE DEEP MOISTURE PLUME  
DIRECTLY ACROSS THE AREA. THE MAIN HEIGHT FALLS ASSOCIATED WITH THE  
INBOUND MID-LEVEL TROUGH ARE SLATED TO ARRIVE OVERNIGHT TUESDAY  
NIGHT, BUT A SHORTWAVE ARRIVING AHEAD OF THIS WILL OFFER INCREASING  
CHANCES FOR CONVECTION ALONG THE FRONT TUESDAY AFTERNOON. THIS  
SHOULD PROVIDE SOME RELIEF FROM THE HEAT BUT MAY ALSO POSE A THREAT  
FOR POCKETS OF HEAVY RAINFALL. POST-FRONTAL HIGH PRESSURE THEN  
BUILDS IN FROM THE NORTH AND OFFERS DRIER CONDITIONS LATE WEDNESDAY  
INTO THURSDAY WITH HIGH TEMPERATURES MODERATING BACK INTO THE MID  
80S.  
 

 
   
MARINE
 
 
VERY WARM SOUTHERLY FLOW IN PLACE FOR THE REST OF THE WEEKEND, WITH  
STRONG NEAR WATER STABILITY LEADING TO WINDS HOLDING AROUND 20 KNOTS  
FOR THE MOST PART. DRY MID LEVELS IN PLACE OVER THE CENTRAL GREAT  
LAKES WILL MOSTLY CAP THUNDERSTORM ACTIVITY, BUT A FEW STORMS ARE  
LIKELY TO SNEAK INTO THE NORTHERN SECTIONS OF LAKE HURON BY THE END  
OF THE WEEKEND AS A DISSIPATING COLD FRONT TRACKS THROUGH.  
 
BY EARLY NEXT WEEK, A SECOND LOW DEVELOPS OVER SOUTHERN ONTARIO AND  
TRACKS JUST NORTH OF LAKE SUPERIOR, DRAWING A MORE SIGNIFICNAT COLD  
FRONT THROUGH THE AREA AND CLEARING OUT THE WARM/HUMID AIRMASS MID-  
WEEK. THIS FRONT WILL LIKELY TRIGGER SHOWERS AND THUNDERSTORMS.  
SOUTHWEST WINDS SHIFT TO THE NORTHWEST AS A RESULT OF THIS FRONTAL  
PASSAGE AS WELL.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 1232 PM EDT SAT AUG 9 2025  
 
AVIATION...  
 
THE PERSISTENCE OF LOW TO MID LEVEL HIGH PRESSURE ACROSS THE MID  
ATLANTIC AND EASTERN GREAT LAKES WILL MAINTAIN STRONG STABILITY  
ACROSS SE MI TODAY AND TONIGHT, WHICH WILL INHIBIT LATE DAY  
CONVECTIVE DEVELOPMENT. THERE WILL BE ENOUGH LOW LEVEL MOISTURE TO  
SUPPORT A SCATTERED DIURNAL CU FIELD. THE SOUTHERLY GRADIENT AND  
DAYTIME HEATING WILL SUSTAIN SOUTH WINDS AROUND 10 KNOTS. WINDS WILL  
WEAKEN SLIGHTLY WITH THE ONSET OF NIGHTTIME COOLING THIS EVENING.  
 
FOR DTW/D21 CONVECTION... THUNDERSTORMS ARE NOT EXPECTED THROUGH  
THE TAF PERIOD.  
 
THRESHOLD PROBABILITIES...  
 
* NONE.  
 

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

 
 

 
 
DISCUSSION...TF  
MARINE.......SF  
AVIATION.....SC  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT.  
 
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