776
FXUS63 KGRR 021533
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1133 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
UPDATE
ISSUED AT 1116 AM EDT WED SEP 2 2026
12Z GUIDANCE IS TRENDING DRIER TODAY WITH LIMITED POTENTIAL FOR
ANY ORGANIZED CONVECTION EVEN AFTER THE CAP ERODES THIS AFTERNOON.
THE BEST CHANCE FOR A SCATTERED SHOWER OR STORM WOULD BE NORTH OF
M-20 THIS AFTERNOON AND EVENING AS WELL AS NEAR AND EAST OF US
127. AN ISOLATED INSTANCE FOR A STRONG WIND GUST OR SOME HAIL MAY
OCCUR WITH CONVECTION THAT TRIES TO GET GOING TODAY. MOST AREAS
WON'T GET THUNDERSTORMS. THE BETTER SETUP ACTUALLY LOOKS TO OCCUR
WELL AFTER DARK TONIGHT WITH SOME ELEVATED THUNDERSTORMS
POTENTIALLY MOVING IN CLOSER TO 06Z AND BEYOND. THOSE COULD
PRODUCE SIZABLE HAIL AND HEAVY DOWNPOURS BUT A LOW LEVEL
INVERSION SHOULD LIKELY KEEP STRONG WINDS AT BAY.
THE HEAT ADVISORY WAS EXPANDED ONE ROW OF COUNTIES TO THE NORTH
FOR TODAY WITH HEAT INDEX READINGS ALREADY AROUND 90 THIS MORNING
WITH GOOD POTENTIAL FOR 95 TO 100 ACROSS THE ADVISORY AREA TODAY.
WILL CONTINUE TO ASSESS 12Z TRENDS TO SEE IF A FURTHER NORTHWARD
EXPANSION IS NEEDED.
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 /12Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 715 AM EDT WED SEP 2 2026
THREAT FOR THUNDERSTORMS REMAINS THE MAIN QUESTION MARK TODAY.
STORMS HAVE REMAINED NORTH OF THE TAF SITES OVERNIGHT. OUTFLOW
BOUNDARIES FROM THE STORMS TO THE NORTH WILL PUSH IN THIS MORNING
TOWARDS I-96. WE HAVE PUT VCTS IN THE TAF SITES FROM 16Z-20Z TO
ACCOUNT FOR STORMS DEVELOPING NEAR THESE OUTFLOW BOUNDARIES TODAY.
VFR WEATHER WILL LARGELY PREVAIL TODAY AND TONIGHT OUTSIDE OF
POTENTIAL THUNDERSTORMS.
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 UNTIL 8 PM EDT THIS EVENING FOR MIZ064>067-071>074.
MARINE...NONE.
UPDATE...HOVING
DISCUSSION...DUKE
AVIATION...DUKE
MARINE...DUKE
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