249  
FXUS63 KDTX 181938  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
338 PM EDT MON AUG 18 2025  
   
KEY MESSAGES
 
 
- DRY WEATHER TODAY AND MOST OF TONIGHT.  
 
- SCATTERED SHOWERS AND STORMS BECOME POSSIBLE LATE TONIGHT THROUGH  
TUESDAY EVENING. LOCALLY HEAVY RAINFALL IS THE PRIMARY CONCERN WITH  
THIS ACTIVITY.  
 
- THERE IS A MARGINAL RISK OF SEVERE STORMS FOR FAR SOUTHEASTERN  
MICHIGAN TUESDAY AFTERNOON EAST OF A LINE FROM PORT HURON TO ADRIAN.  
 
- SEASONABLE TEMPERATURES AND DRY WEATHER MOVE IN AND HOLD WEDNESDAY  
THROUGH FRIDAY.  
 

 
   
DISCUSSION
 
 
REGIONAL SATELLITE IMAGERY SHOWS THE EXTENSIVE CLOUD FIELD  
ASSOCIATED WITH THE LOW PRESSURE SYSTEM OVER MN/WI THIS AFTERNOON  
THAT WE WILL BE FOCUSING ON FOR CONVECTIVE CHANCES THROUGH LATE  
TUESDAY. WITH LOW AMPLITUDE RIDGE AXIS FOLDING OVER THE REGION IN  
THE MID LEVELS, THE LOW WILL DRIFT EASTERLY FROM SOUTHERN WI TONIGHT  
INTO CENTRAL LOWER MI BY TUESDAY MORNING. IN ADVANCE OF THIS, THE  
850MB THETA E GRADIENT WILL LIFT NORTHEAST THROUGH LOWER MI TONIGHT  
ON THE NOSE OF THE LOW LEVEL JET, HELPING TO FUEL A ROUND OF SHOWERS  
AND ELEVATED THUNDERSTORMS. THIS ACTIVITY WOULD BE MOSTLY NORTH OF  
I69. MORE WIDESPREAD ACTIVITY WILL MOVE IN FROM WEST TO EAST AROUND  
10-14Z AS THE LOW LEVEL JET AND DRAPING WARM FRONT PUSH THROUGH THE  
AREA. LOW RISK OF SEVERE WEATHER WITH THE EARLY ROUND OF MOSTLY  
ELEVATED STORMS, LOW SHEAR AND JUST A FEW HUNDRED J/KG OF MUCAPE.  
 
A NARROW WARM SECTOR WILL TRAVERSE THE AREA THROUGH THE AFTERNOON  
PROVIDING ANOTHER ROUND OF MORE WIDESPREAD SHOWERS AND STORMS.  
CURRENTLY THE LOW LOOKS TO PASS THROUGH THE THUMB WHICH WILL BRING  
THE WARM SECTOR THROUGH DURING PEAK HEATING, ALBEIT MUTED DUE TO  
LIKELIHOOD OF CLOUDY SKIES. CAMS SUGGEST THERE COULD STILL BE AROUND  
1000 J/KG OF SURFACE BASED CAPE WITH >20 KNOTS OF SHEAR WHILE THE  
WEAKENING LOW LEVEL JET PASSES OVER JUST AHEAD OF THE COLD FRONT.  
ADDING TO THE SYNOPTIC SUPPORT WILL BE A 500MB SHORTWAVE ADVANCING  
OVER THE REGION. SPC CLIPPED A SMALL PORTION OF SE MI WITH A  
MARGINAL RISK FROM ABOUT PORT HURON TO ADRIAN AND EASTWARD. THIS  
WILL ALL BE DEPENDENT ON WHERE THE SURFACE LOW ACTUALLY TRACKS. SOME  
EARLIER GUIDANCE HAD THE LOW A BIT FURTHER SOUTH.  
 
MAIN RISK WITH THE STORMS TONIGHT AND TUESDAY WILL BE HEAVY RAIN AND  
LOCALIZED FLOODING. THE OVERNIGHT STORMS APPEAR TO BE FAIRLY  
PROGRESSING, BUT AS THE LOW DRIFTS ACROSS THE AREA, THERE IS  
POTENTIAL FOR SLOWER MOVING STORMS AROUND THE LOW CENTER WITH AMPLE  
MOISTURE AS PWATS RISE TO JUST OVER 2 INCHES (WITH SURFACE DEWPOINTS  
ONCE AGAIN AT OR ABOVE 70) WITH STRONG MOISTURE ADVECTION. STRONG TO  
SEVERE WIND GUSTS WILL BE ANOTHER CONCERN WITH THESE STRONGER  
STORMS.  
 
THE BULK OF THE ACTIVITY WILL BE DONE IN THE EVENING BUT THERE IS A  
CHANCE THAT THE WRAP AROUND MOISTURE AND DEFORMATION BAND COULD KEEP  
SOME SHOWERS AROUND AFTER 00Z FOR A FEW HOURS. OTHERWISE, HIGH  
PRESSURE WILL RETURN TO THE GREAT LAKES OUT OF CANADA WITH  
NORTHEASTERLY WINDS ACROSS THE REGION. THIS WHILE THE UPPER LEVEL  
RIDGE BUILDS BACK OVER THE WESTERN/CENTRAL CONUS AND BEGINS PUSHING  
INTO LOWER MI.  
 
CONTINUED OCCLUSION OF THE SURFACE FRONTAL SYSTEM, AND A BOOST FROM  
THE 500 MB WAVE, RESULT IN SECONDARY LOW PRESSURE NEAR THE OHIO  
BORDER AND A LINGERING CHANCE OF SHOWERS IN SE MI TUESDAY EVENING.  
THE LOW PRESSURE SYSTEM MAKES A MORE AGGRESSIVE MOVE TO EXIT  
EASTWARD AS THE EFFECTIVE FRONTAL PASSAGE BY WEDNESDAY MORNING  
FOLLOWED BY INCREASING NORTH WIND ACROSS LOWER MI THAT BRINGS IN  
ANOTHER ROUND OF COOLER AND LESS HUMID AIR. THE 18/00Z MODEL RUN IS  
IN GOOD AGREEMENT ON SOLUTIONS THAT SHOW THE LONG WAVE RIDGE  
BUILDING BACK NORTH INTO CENTRAL CANADA AND THEN LEANING EASTWARD  
OVER THE GREAT LAKES DURING THE LATE WEEK. THIS IS FOLLOWED BY A  
LARGER/STRONGER CANADIAN LOW PRESSURE SYSTEM SET TO BRING THE NEXT  
COLD FRONT THROUGH LOWER MI TO START NEXT WEEKEND. TEMPERATURES WILL  
HOVER AROUND 80 MID WEEK BEFORE SLOWLY CLIMB THROUGH THE END OF THE  
WEEK WITH A CHANCE OF THE RIDGE AXIS FOLDING OVER THROUGH THE REGION  
ON FRIDAY BRINGING MID 80S BACK FOR A DAY.  
 

 
   
MARINE
 
 
HIGH PRESSURE CENTERED OVER SOUTHERN QUEBEC MAINTAINS EAST TO EAST-  
SOUTHEAST WIND THIS AFTERNOON THAT GRADUALLY SHIFTS SOUTHEAST AND  
STRENGTHENS TONIGHT AS A LOW PRESSURE SYSTEM TRACKS IN FROM THE  
MIDWEST. GUSTS TO AROUND 25 KNOTS WILL BE LOCALIZED ACROSS NORTHERN  
LAKE HURON GIVEN FAVORABLE FETCH AND CHANNELING EFFECTS. SCATTERED  
TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL ACCOMPANY THE LOW  
PRESSURE THROUGH THE CENTRAL GREAT LAKES OVERNIGHT AND THROUGH THE  
DAY TUESDAY. GUSTY SOUTHEAST WINDS TO AROUND 15 TO 20 KNOTS WILL  
PERSIST ACROSS LAKE HURON DURING THIS PERIOD. THE LOW PASSES EAST  
CAUSING WIND TO SHIFT TO NORTHEAST LATE TUESDAY NIGHT INTO  
WEDNESDAY, REACHING A PEAK OF 20 TO 25 KNOTS WEDNESDAY AFTERNOON  
WITH SOME GUSTS UP TO 30 KNOTS POSSIBLE ALONG THE SOUTHERN LAKE  
HURON SHORELINE. SMALL CRAFT ADVISORIES ARE LIKELY THROUGH WEDNESDAY  
EVENING AS WAVES BUILD TO 4+ FEET. HIGH PRESSURE THEN BUILDS IN FROM  
THE NORTHERN GREAT LAKES THROUGH THE LATE WEEK WITH NORTHEAST WIND  
BECOMING LIGHT.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 155 PM EDT MON AUG 18 2025  
 
AVIATION...  
 
A DEEP LOW PRESSURE SYSTEM WILL ORGANIZE OVER NORTHERN WISCONSIN  
TODAY AND DIG SOUTHEASTWARD INTO SOUTHEAST MICHIGAN ON TUESDAY. A  
SHARP MOISTURE GRADIENT WILL PRECEDE THE LOW PRESSURE SYSTEM AND  
LEAD TO MOISTURE ADVECTION TONIGHT. THERE IS A POTENTIAL PERIOD FOR  
SHOWERS AND THUNDERSTORMS AT KMBS AND KFNT AFTER 08Z TONIGHT, BEFORE  
CHANCES INCREASE AT ALL TAF SITES BETWEEN 13-16Z. INTRODUCED A TEMPO  
GROUP FOR TSRA AT THE DETROIT TAF SITES. DIURNAL MVFR CIG HEIGHTS  
THIS AFTERNOON WILL LIFT TO VFR. PREVAILING VFR IS ANTICIPATED  
TONIGHT. BRIEF IFR TO LIFR CONDITIONS WILL BE POSSIBLE WITH HEAVY  
RAINFALL.  
 
FOR DTW/D21 CONVECTION...THUNDERSTORM ACTIVITY IS POSSIBLE AFTER 13Z  
TUESDAY.  
 
THRESHOLD PROBABILITIES...  
 
* LOW FOR THUNDERSTORMS AFTER 13Z TUESDAY.  
 

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

 
 

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