749
FXUS63 KGRR 120622
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
222 AM EDT TUE AUG 12 2025
KEY MESSAGES
- SCATTERED SHOWERS AND STORMS TODAY AND TONIGHT
- SHOWERS AND STORMS LIKELY TUESDAY WITH A FEW SEVERE STORMS POSSIBLE
- COOLER AND DRY LATE WEEK
- HOT THIS WEEKEND WITH SHOWERS/STORMS POSSIBLE
DISCUSSION
ISSUED AT 245 PM EDT MON AUG 11 2025
- SCATTERED SHOWERS AND STORMS TODAY AND TONIGHT
SCATTERED SHOWERS AND STORMS ARE ALREADY DEVELOPING ACROSS PARTS OF
WEST MICHIGAN THIS AFTERNOON DUE TO A LOW-LEVEL CONVERGENCE AXIS.
THE GREATEST CHANCE FOR ANY PRECIPITATION IS EAST OF A CLARE TO
IONIA TO SOUTH HAVEN LINE. WITH EFFECTIVE SHEAR LESS THAN 20 KNOTS,
STORMS WILL BE DISORGANIZED WITH LOCALLY HEAVY RAINFALL AND
LIGHTNING AS THE MAIN THREATS. IF A FEW STRONGER CORES CAN DEVELOP,
ISOLATED GUSTS IN EXCESS OF 40 MPH ARE POSSIBLE. A SECOND ROUND OF
SHOWERS AND STORMS IS EXPECTED ACROSS MUCH OF THE AREA OVERNIGHT
INTO TUESDAY MORNING AS AN MCV CURRENTLY ACROSS NORTHEAST KANSAS
ACTS IN CONCERT WITH THE LOW-LEVEL JET. ONCE AGAIN, A FEW STORMS
WITH GUSTY WINDS CANNOT BE RULED OUT THOUGH CONFIDENCE IS LOW.
- SHOWERS AND STORMS LIKELY TUESDAY WITH A FEW SEVERE STORMS POSSIBLE
ATTENTION THEN TURNS TO TUESDAY AFTERNOON, WHEN A DYING COLD FRONT
THAT STALLS ACROSS NORTHWEST MICHIGAN MONDAY NIGHT LIKELY SERVES AS
THE FOCUS FOR CONVECTIVE DEVELOPMENT IN THE AFTERNOON AND EVENING.
EVEN WITH A WARM PROFILE SUPPORTIVE OF MARGINAL MID-LEVEL LAPSE
RATES, A VERY MOIST PROFILE IN CONJUNCTION WITH DIURNAL HEATING
WILL LEAD TO AMPLE CAPE TO SUPPORT THUNDERSTORMS. THE ARRIVAL OF A
35-40 KNOT 700 MB JET IN THE AFTERNOON WILL INCREASE DEEP LAYER
SHEAR TO THE 25-35 KNOT RANGE ALLOWING SOME POTENTIAL FOR
CONVECTIVE ORGANIZATION. THE HREF CAPTURES THIS WELL WITH UH
SWATHS ACROSS THE SOUTHERN HALF OF THE CWA IN THE AFTERNOON AND
EVENING.
THIS WILL BRING THE POTENTIAL FOR STRONG TO SEVERE STORMS TUESDAY
AFTERNOON AND EVENING. THE PRIMARY CONCERN IS FOR DAMAGING WIND
GUSTS TO AROUND 60 MPH IN ANY TRANSIENT SUPERCELL STRUCTURES OR
BOWING SEGMENTS THAT DEVELOP. LOCALLY HEAVY RAINFALL WILL ALSO BE A
CONCERN GIVEN THE VERY MOIST AIRMASS WITH THE HREF 24 HR LPMM
SUGGESTING THAT ANY AREAS WITH TRAINING STORMS MAY SEE RAINFALL OVER
3 INCHES. THE BEST CHANCE FOR THIS IS ACROSS SOUTHERN MICHIGAN.
- COOLER AND DRY LATE WEEK
MID-LEVEL TROUGHING PERSISTS OVER THE AREA FOR WEDNESDAY KEEPING
850MB TEMPS IN THE MID TEENS CELSIUS. THIS WILL KEEP CONDITIONS
RELATIVELY COOL WEDNESDAY INTO THURSDAY WITH HIGHS IN THE LOW 80S.
AS FOR PRECIPITATION, CANNOT RULE OUT ISOLATED SHOWERS TO START THE
DAY WEDNESDAY ACROSS OUR SOUTHEAST FORECAST AREA AS THE COLD FRONT
EXITS. THEN SURFACE RIDGING TAKES OVER WITH DRY CONDITIONS EXPECTED
THROUGH THE REST OF THE WORK WEEK. DEWPOINTS IN THE UPPER 50S TO LOW
60S WILL ALSO FEEL MORE COMFORTABLE THAN RECENT DAYS.
- HOT THIS WEEKEND WITH SHOWERS/STORMS POSSIBLE
UPPER LEVEL RIDGING RETURNS THIS WEEKEND WITH 850MB TEMPS CLIMBING
INTO THE LOW 20S CELSIUS TRANSLATING INTO HIGH TEMPS IN THE UPPER
80S TO LOW 90S ONCE AGAIN. SHOWERS AND STORMS ARE POSSIBLE AS AN MCS
COMPLEX TRIGGERED OFF OF A FRONTAL BOUNDARY MAY DEVELOP. WHERE ANY
SUCH COMPLEX WOULD PROPAGATE IS UNCERTAIN AT THIS RANGE WITH
POSSIBLE SCENARIOS INCLUDING STORMS STAYING NORTH OF WEST MICHIGAN
OR MAKING IT INTO PART OR MOST OF THE AREA.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 222 AM EDT TUE AUG 12 2025
MULTIPLE ROUNDS OF THUNDERSTORMS ARE LIKELY TODAY, BUT EXACT
TIMING WILL BE DIFFICULT GIVEN THE HUMID AND UNSTABLE ATMOSPHERE
IN PLACE WHICH WILL BE READY TO POP OFF THUNDERSTORM CELLS WITH
LITTLE FORCING. ONGOING SCATTERED THUNDERSTORMS SHOULD WEAKEN OR
MOVE OUT AROUND 10 TO 11 Z, THEN WE MAY CATCH A FEW HOUR BREAK
UNTIL THE NEXT STORM COMPLEX FROM ILLINOIS ARRIVES LATER IN THE
MORNING. AFTER THAT PASSES, ADDITIONAL THUNDERSTORMS MAY DEVELOP
IN ITS WAKE DURING THE AFTERNOON, POSSIBLY LINGERING PAST 00 Z.
THE DAYTIME THUNDERSTORMS ARE FAVORED TO PRODUCE LLWS AND SOME
LOCATIONS COULD HAVE SURFACE WIND GUSTS 35 TO 50 KNOTS.
MARINE
ISSUED AT 135 PM EDT MON AUG 11 2025
WIND AND WAVES WILL DIMINISH LATE THIS AFTERNOON AND EVENING AND
REMAIN RELATIVELY LIGHT FOR THE NEXT FEW DAYS. MARINE AND BEACH
HAZARDS WILL EXIST FOR THE REMAINDER OF THIS AFTERNOON.
SCATTERED THUNDERSTORMS WILL REMAIN A HAZARD TO BOATERS AND BEACH
GOERS THROUGH TUESDAY NIGHT.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...THOMAS
AVIATION...CAS
MARINE...04
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