598
FXUS63 KGRR 121157
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
757 AM EDT TUE AUG 12 2025
KEY MESSAGES
- SHOWERS AND STORMS LIKELY TODAY, A FEW SEVERE STORMS POSSIBLE
- COOLER AND DRY LATE WEEK
- HOT THIS WEEKEND WITH SHOWERS/STORMS POSSIBLE
DISCUSSION
ISSUED AT 353 AM EDT TUE AUG 12 2025
- SHOWERS AND STORMS LIKELY TODAY, A FEW SEVERE STORMS POSSIBLE
A LINE OF THUNDERSTORMS ROLLING THROUGH NORTHERN ILLINOIS EARLY
THIS MORNING MAY BE ARRIVING IN WEST MICHIGAN AS EARLY AS 9 AM.
MUCAPE AROUND 1000 J/KG IS PRESENT OVER OUR AREA AND CAPPING WILL
BE MINIMAL, SO THE STORMS SHOULD SURVIVE ACROSS THE LAKE AND
COULD ALSO PRODUCE GUSTS GREATER THAN 40 MPH. IT'S NOT ENTIRELY
CLEAR WHETHER THE SOUTHERN EXTENT OF THIS CONVECTION WILL BECOME
THE MAIN EVENT FOR SOUTHERN MICHIGAN, IN WHICH CASE THE THREAT
WILL DIMINISH AFTER 4 PM, OR WHETHER IT WILL LEAVE BEHIND A
BOUNDARY FOR ADDITIONAL STORMS TO FIRE ALONG DURING THE EVENING.
DEEP LAYER SHEAR AROUND 25 KNOTS AND THE POTENTIAL FOR SLIGHTLY
ELONGATED HODOGRAPHS IN THE 0-3 KM LAYER MAY SUPPORT SOME LIMITED
ORGANIZATION, EITHER BOWING OR TRANSIENT SUPERCELL STRUCTURES. THE
MARGINAL SEVERE THREAT OF THE DAY IS PRIMARILY WIND.
GIVEN THE HUMID ATMOSPHERE AND PW 1.75 INCHES OR HIGHER, THE
STORMS WILL HAVE EFFICIENT RAINFALL RATES. SPOTTY RAIN TOTALS
AROUND 3 INCHES ARE POSSIBLE PER THE HREF LPMM.
- COOLER AND DRY LATE WEEK
ISSUED AT 245 PM EDT MON AUG 11 2025
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
ISSUED AT 245 PM EDT MON AUG 11 2025
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 /12Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 757 AM EDT TUE AUG 12 2025
NEED TO CARRY PROB30 THUNDERSTORMS MOST OF THE DAY AND WILL ADJUST
TO TEMPO AS NEEDED, DUE TO HUMID AND UNSTABLE ATMOSPHERE IN
PLACE. LINE OF THUNDERSTORMS IS EXPECTED TO CROSS LAKE MICHIGAN
AND MUCH OF CENTRAL WESTERN/CENTRAL LOWER MICHIGAN, POSSIBLY
EXTENDING INTO SOUTHERN MICHIGAN THIS MORNING. OTHER SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS ARE DEVELOPING AHEAD OF THE
STORM LINE'S ARRIVAL. SUBSEQUENT SCATTERED THUNDERSTORMS MAY
CONTINUE TO DEVELOP THROUGH EVENING, BUT WITH NOT MUCH CLARITY IN
WHEN IT WILL AFFECT EACH AERODROME AS IT WILL DEPEND ON THE
EVOLUTION OF THE FIRST STORM LINE. LLWS AND SURFACE GUSTS 35 TO
50 KNOTS ARE POSSIBLE WITH SOME OF THE STRONGER STORM CELLS.
MARINE
ISSUED AT 353 AM EDT TUE AUG 12 2025
MODERATE SWIM RISK POSSIBLE WITH OCCASIONAL THUNDERSTORMS OVER
LAKE MICHIGAN TODAY. SOME THUNDERSTORMS COULD PRODUCE WIND GUSTS
BRIEFLY OVER 35 KNOTS. OTHER AREAS OUTSIDE OF THUNDERSTORMS COULD
HAVE OCCASIONS OF 15-20 KNOT WINDS KICKING UP 2 TO 4 FT WAVES.
NORTH TO NORTHWEST WINDS ON WEDNESDAY MAY CONTINUE A MODERATE SWIM
RISK SOUTH OF WHITEHALL TOWARD ST JOSEPH.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...CAS/THOMAS
AVIATION...CAS
MARINE...CAS
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