268  
FXUS63 KGRR 260755  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
355 AM EDT SAT JUL 26 2025  
   
KEY MESSAGES  
 
- POTENTIALLY A COUPLE ROUNDS OF SHOWERS AND STORMS TODAY  
 
- ANOTHER CHANCE FOR SHOWERS AND STORMS ON MONDAY  
 
- TURNING DRIER AND COOLER MID TO LATE WEEK  
 
 
   
DISCUSSION  
 
ISSUED AT 355 AM EDT SAT JUL 26 2025  
 
- POTENTIALLY A COUPLE ROUNDS OF SHOWERS AND STORMS TODAY  
 
A SERIES OF WEAK CONVECTIVELY INDUCED VORT MAXIMA ARE LOCATED  
WITHIN SOUTHWEST FLOW ALOFT STRETCHING FROM NORTHERN INDIANA  
SOUTHWEST TO NORTHEAST KANSAS. THESE VORT MAXIMA WILL TRAVERSE THE  
SOUTHERN GREAT LAKES REGION FROM EARLY THIS MORNING THROUGH THIS  
EVENING, LIKELY RESULTING IN ROUNDS OR PERIODS OF SHOWERS AND  
THUNDERSTORMS. THE FIRST PERIOD WE EXPECT STORMS IS TOWARDS  
DAYBREAK AND THROUGH THE MORNING HOURS. BOTH HIGH RESOLUTION AND  
GLOBAL MODELS INDICATE A SURGE IN THE NOCTURNAL LOW LEVEL JET  
AIMED RIGHT INTO SOUTHWEST LOWER MICHIGAN AROUND 800AM. WE ARE NOT  
TOO CONCERNED ABOUT SEVERE WEATHER WITH THIS WAVE OF ACTIVITY, BUT  
LOCALLY HEAVY RAIN IS QUITE POSSIBLE GIVEN PWAT VALUES APPROACHING  
2.25 INCHES. LOCAL SWATHS OF 1-2 INCHES OF RAIN LOOK LIKE A GOOD  
BET THIS MORNING PER THE HREF.  
 
WE MAY SEE A LULL IN THE ACTIVITY IN THE EARLY TO MID AFTERNOON IN  
THE WAKE OF THE MORNING CONVECTION FOLLOWED BY ANOTHER POTENTIAL  
ROUND IN THE LATE AFTERNOON AND ESPECIALLY THE EVENING HOURS AS  
THE LAST IN THE TRAIN OF SHORTWAVES WORK THROUGH THE SOUTHERN  
GREAT LAKES. THERE IS A SURGE IN WIND SPEEDS THIS AFTERNOON AND  
EVENING WITH THE 850MB LLJ INCREASING TO AROUND 30 KNOTS AND THE  
MID LEVEL JET AT 500MB INCREASING TO 40+ KNOTS. DEEP LAYER SHEAR  
INCREASES TO 30-35 KNOTS SO STORM ORGANIZATION CAN BE EXPECTED. IF  
WE CAN REALIZE ENOUGH INSTABILITY THIS AFTERNOON IN THE WAKE OF  
THE MORNING PRECIPITATION A MARGINAL SEVERE WEATHER THREAT EXISTS  
(WE ARE IN A SPC MARGINAL THREAT TODAY). MAIN THREAT LOOKS TO BE  
WIND WITH THIS ACTIVITY. THREAT AREA LOOKS TO BE FROM THE I-96  
CORRIDOR TO THE SOUTH. MULTIPLE ROUNDS OF RAIN TODAY INTO EARLY  
TONIGHT MAY PUT DOWN 2.00 TO 3.00+ INCHES OF RAIN IN SPOTS PER THE  
HREF. WE SHOULD BE ABLE TO ABSORB THIS RAINFALL INTO THE RIVERS  
WITHOUT MUCH OF AN ISSUE, BUT SHORT TERM PONDING OF WATER MAY  
OCCUR IN THE TORRENTIAL DOWNPOURS.  
 
- ANOTHER CHANCE FOR SHOWERS AND STORMS ON MONDAY  
 
ANOTHER ROUND OF SHOWERS AND STORMS LOOKS POSSIBLE ON MONDAY WITH  
A WEAK COLD FRONT MOVING THROUGH THE REGION. THE MAIN SHORTWAVE IS  
WELL OFF TO OUR NORTH HOWEVER AND THE CHANCES FOR WIDESPREAD  
PRECIPITATION LOOK SMALLER THAN THEY DID A DAY OR TWO AGO FOR  
MONDAY. STILL, SOME SCATTERED SHOWERS AND STORMS LOOK LIKE A GOOD  
FORECAST, ESPECIALLY ACROSS CENTRAL LOWER MICHIGAN CLOSER TO THE  
UPPER SUPPORT.  
 
- TURNING DRIER AND COOLER MID TO LATE WEEK  
 
WE LOOK TO TURN COOLER AND DRIER AS WE HEAD INTO THE WEDNESDAY  
THROUGH FRIDAY PERIOD. A LARGE UPPER LOW OVER EASTERN CANADA  
NUDGES SOUTHWARD INTO THE GREAT LAKES REGION DURING THIS TIME  
FRAME RESULTING IN COOLER AIR INFILTRATING THE AREA AT 850MB. BY  
FRIDAY 850MB TEMPERATURES ACTUALLY DIP TO +8C TO +9C WHICH SHOULD  
RESULT IN VERY PLEASANT TEMPERATURES FOR THOSE LOOKING FOR A  
RESPITE FROM THE HEAT AND HUMIDITY. OUR FORECAST HIGHS BY THE END  
OF THE WEEK ARE IN THE 70S WITH DEW POINTS EVEN DIPPING INTO THE  
40S. THE LATTER HALF OF THE WORK WEEK LOOKS DRY WITH SURFACE HIGH  
PRESSURE FIRMLY IN CONTROL.  
 
 
   
AVIATION /06Z TAFS THROUGH 06Z SUNDAY/  
 
ISSUED AT 155 AM EDT SAT JUL 26 2025  
 
A WARM FRONT IS SITUATED FROM NORTHERN ILLINOIS EASTWARD INTO  
LOWER MICHIGAN NEAR INTERSTATE 94 AT 06Z. THIS WARM FRONT WILL  
BRING CHANGES IN THE WEATHER TO ALL THE TAF SITES THIS MORNING.  
FIRST, THE FRONT WILL AID IN LOWER CLOUD PRODUCTION WITH MVFR AND  
IFR CEILINGS EXPECTED TO DEVELOP BETWEEN 09Z AND 12Z. ALSO, THE  
FRONT WILL PRODUCE NUMEROUS SHOWERS AND THUNDERSTORMS THAT WILL  
DEVELOP BETWEEN 09Z AND 12Z AND SWEEP THROUGH ALL OF THE TAF SITES  
BETWEEN 12Z AND 16Z. POOR AVIATION CONDITIONS WILL OCCUR DURING  
THIS TIME AS IFR AND MVFR CONDITIONS WILL BE REINFORCED BY THE  
RAIN AND FRONT.  
 
DURING THE AFTERNOON, HAVE WRITTEN OPTIMISTIC TAFS WITH VCSH  
WORDING AND CONDITIONS TURNING VFR. IT IS VERY POSSIBLE HOWEVER  
THAT ADDITIONAL MORE WIDESPREAD SHOWERS/STORMS MAY DEVELOP. A  
GENERAL IMPROVING TREND THOUGH IS EXPECTED AS WE HEAD FROM THE  
DAYLIGHT MORNING HOURS INTO THE AFTERNOON. WINDS WILL BECOME  
SOUTHWEST TODAY AT 5-15 KNOTS.  
 
 
   
MARINE  
 
ISSUED AT 355 AM EDT SAT JUL 26 2025  
 
THE QUIET CONDITIONS OUT ON THE BIG LAKE LOOK TO CONTINUE THROUGH  
THE WEEKEND AND INTO MONDAY AND MONDAY NIGHT. THE LIGHT WINDS  
INITIALLY THIS WEEKEND ARE PROVIDED BY SURFACE RIDGING MEANING A  
FAIRLY SLACK GRADIENT IN PLACE. INTO EARLY NEXT WEEK A WEAK FRONT  
MOVES THROUGH WHICH KEEPS THE GRADIENT ON THE SLACK SIDE. SO, WE  
ARE EXPECTING WINDS GENERALLY IN THE 5 TO 15 KNOT RANGE THE NEXT 3  
DAYS OR SO WITH WAVES OF 2 FEET OR LESS. WINDS AND WAVES WILL BE  
BRIEFLY HIGHER IN AND NEAR THUNDERSTORMS BOTH TODAY AND AGAIN ON  
MONDAY.  
 
 
   
GRR WATCHES/WARNINGS/ADVISORIES  
 
MI...NONE.  
MARINE...NONE.  
 
 
 
 
 
DISCUSSION...DUKE  
AVIATION...DUKE  
MARINE...DUKE  
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