080
FXUS63 KGRR 020736
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
336 AM EDT WED SEP 2 2026
KEY MESSAGES
- A COUPLE ROUNDS OF SHOWERS/STORMS TODAY
- ADDITIONAL SHOWERS/STORMS ON THURSDAY
- STORM CHANCES COULD LINGER INTO FRIDAY/SATURDAY
DISCUSSION
ISSUED AT 335 AM EDT WED SEP 2 2026
- A COUPLE ROUNDS OF SHOWERS/STORMS TODAY
MUCAPE VALUES EARLY THIS WEDNESDAY MORNING ARE A VERY RESPECTABLE
1,500 TO 3,000 J/KG. UPSTREAM CONVECTION CONTINUES TO FILL IN, IN
AN EAST/WEST ZONE ACROSS WISCONSIN. A WEAKER LOW LEVEL JET AROUND
30 KNOTS IS DRIVING THIS CONVECTION. WE EXPECT IT TO CONTINUE TO
SLIDE EAST AND/OR DEVELOP OVER OUR CWA FROM I-96 TO THE NORTH.
CANNOT RULE OUT SEVERE WEATHER THIS MORNING GIVEN THE
AFOREMENTIONED INSTABILITY AND DEEP LAYER SHEAR OF 40 KNOTS. BOTH
HAIL AND STRONGER WIND GUSTS ARE POSSIBLE. SOME HIGH RESOLUTION
MODELS INDICATE A FEW SWATHS OF SEVERE WIND. WE WILL BE MONITORING
AS THE ACTIVITY CONTINUES TO BUILD IN.
GIVEN WESTERLY UPPER FLOW THAT WILL RESULT IN TRAINING OF CELLS
AS WELL AS A PERSISTENT INFLUX OF HIGH PWAT AIR FROM THE SOUTH,
HEAVY RAIN IS CERTAINLY POSSIBLE.
ANOTHER ROUND OF SHOWERS AND STORMS IS POSSIBLE THIS AFTERNOON AND
EVENING AND SPC HAS MUCH OF OUR FORECAST IN A SLIGHT RISK FOR
SEVERE WEATHER. MUCAPE VALUES WILL RECOVER TO IN EXCESS OF 2,000
J/KG WITH DEEP LAYER SHEAR ON THE ORDER OF 30 KNOTS. MACHINE
LEARNING SCHEMES FAVOR AREA OFF TO OUR EAST INTO THE THUMB MORE
THAN OUR AREA, BUT ADDITIONAL SEVERE WEATHER CANNOT BE RULED OUT.
SARS SOUNDING ANALOGS VIA THE HRRR SHOW A FAIRLY BIG SIGNAL FOR
LARGE HAIL. DCAPE VALUES ARE IN EXCESS OF 1,000 J/KG SO SEVERE
GUSTS ARE ALSO POSSIBLE. BOTTOM LINE TODAY COULD BE AN ACTIVE DAY
(BOTH THIS MORNING AND LATER THIS AFTERNOON) WITH SEVERE WEATHER
AND HEAVY RAIN.
A HEAT ADVISORY HAS BEEN ISSUED FOR THE I-94 CORRIDOR. THIS IS THE
AREA IN THE CWA THAT HAS THE BEST CHANCE AT HITTING 100 APPARENT
TEMPERATURES. IT IS VALID FROM NOON TO 8PM THIS EVENING.
- ADDITIONAL SHOWERS/STORMS ON THURSDAY
LOW LEVEL MOISTURE REMAINS PARKED OVER THE AREA ON THURSDAY WITH A
SURFACE FRONT LINGERING. ADDITIONAL ROUNDS OF SHOWERS AND STORMS
APPEAR LIKELY ON THURSDAY ALTHOUGH CONVERGENCE OF THE LOW LEVEL
JET DOES NOT LOOK IDEAL. THE LOW LEVEL JET WEAKENS THROUGH THE
DAY. SHORTWAVE ACTIVITY WILL BE WORKING THROUGH THE AREA HOWEVER
IN ZONAL UPPER FLOW NORTH OF THE RIDGE LOCATED IN THE SOUTHEAST
U.S. THE UPPER SUPPORT COMBINED WITH LOW LEVEL CONVERGENCE
ASSOCIATED WITH THE FRONT SHOULD BE ENOUGH TO DRIVE ADDITIONAL
ACTIVITY. DETAILS REMAIN DIFFICULT TO NAIL DOWN HOWEVER AS
CONVECTION TODAY AND TONIGHT WILL AFFECT THE SETUP FOR TOMORROW.
WE ARE IN A SPC MARGINAL FOR SEVERE WEATHER ON THURSDAY.
- STORM CHANCES COULD LINGER INTO FRIDAY/SATURDAY
GFS AND ECWMF ENSEMBLE DATA SHOW QUITE A FEW MEMBERS THAT SUPPORT
MORE SHOWERS AND STORMS FRIDAY AND POTENTIALLY INTO SATURDAY. THE
UPPER FLOW SHIFTS TO THE NORTHWEST AS A RIDGE DEVELOPS IN THE
PLAINS STATES. THERE ARE INDICATIONS THAT CONVECTIVE VORTS WILL BE
DRIVING SOUTHEAST INTO OUR AREA DURING THIS PERIOD. SO, THE BOTTOM
LINE IS WE WILL SEE ADDITIONAL ACTIVITY. WITH REPEATED ROUNDS OF
SHOWERS AND STORMS WE WILL NEED TO KEEP AN EYE ON THE THREAT OF
LOCALLY HEAVY RAIN.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 208 AM EDT WED SEP 2 2026
VFR WEATHER IS IN PLACE ACROSS THE TAF SITES AT 06Z. SOME
OCCASIONAL FOG IS BEING NOTED AT A FEW OB SITES, BUT THIS SHOULD
REMAIN A SHALLOW GROUND FOG DUE TO STRONGER WINDS JUST OFF THE
SURFACE.
THE MAIN FOCUS WITH THIS SET OF TAFS ARE THE CHANCES FOR SHOWERS
AND THUNDERSTORMS OVER THE NEXT 24 HOURS. THERE ARE TWO MAIN TIME
FRAMES OF CONCERN. THE FIRST IS IN THE NEXT 4 TO 6 HOURS AS STORMS
IN WISCONSIN TRY TO PRESS IN FROM THE WEST OR DEVELOP OVERHEAD. IT
APPEARS MKG AND GRR STAND THE BEST CHANCE AT SEEING SCATTERED
SHOWERS/STORMS BUT CANNOT RULE OUT LAN EITHER. THE I-94 TAF SITES
EARLY THIS MORNING WILL LIKELY BE SPARED AS THE THREAT LOOKS TO BE
FROM I-96 TO THE NORTH. AS FOR IMPACTS, LOCALLY HEAVY RAIN WILL BE
THE MAIN ONE WITH THE POTENTIAL FOR MVFR AND IFR WEATHER. CANNOT
RULE OUT SOME STRONGER WIND GUSTS AS WELL, ESPECIALLY AT MKG (35+
KNOTS POSSIBLE).
A LULL WILL LIKELY OCCUR THROUGH A GOOD PORTION OF THE DAY WITH
ANOTHER ROUND OF STORMS POSSIBLE IN THE LATE AFTERNOON INTO THE
EVENING. THIS ACTIVITY IS LESS LIKELY, BUT WE WILL BE WATCHING.
OUTSIDE OF THE STORMS AND EARLY MORNING LIGHT FOG, VFR WEATHER
SHOULD PREVAIL.
MARINE
ISSUED AT 335 AM EDT WED SEP 2 2026
AN OVERALL LIGHTER WIND REGIME WILL RESULT IN WAVES OF 2 FEET OR
LESS FOR THE NEXT SEVERAL DAYS. GIVEN A SLACK GRADIENT WAVES
PRODUCTION WILL BE DRIVEN BY LOCALIZED INCREASES IN WIND VIA
THUNDERSTORM OUTFLOWS. WINDS AND WAVES WILL BE HIGHER IN AND NEAR
THUNDERSTORMS TODAY THROUGH FRIDAY. WE ARE EXPECTED TO REMAIN
BELOW ADVISORY LEVELS THROUGH FRIDAY.
GRR WATCHES/WARNINGS/ADVISORIES
MI...HEAT ADVISORY FROM NOON TODAY TO 8 PM EDT THIS EVENING FOR
MIZ071>074.
MARINE...NONE.
DISCUSSION...DUKE
AVIATION...DUKE
MARINE...DUKE
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