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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