847
FXUS63 KGRR 151840
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
240 PM EDT TUE SEP 15 2026
KEY MESSAGES
- RAIN CHANCES REMAIN THROUGH WEDNESDAY NIGHT FOR SOUTHERN AREAS
- DRIER WEATHER THURSDAY AND FRIDAY
- STRONGER SYSTEM WITH HEAVY RAIN POTENTIAL SATURDAY
DISCUSSION
ISSUED AT 240 PM EDT TUE SEP 15 2026
- RAIN CHANCES REMAIN THROUGH WEDNESDAY NIGHT FOR SOUTHERN AREAS
MOST AREAS SAW AT LEAST ONE ROUND OF AT LEAST SHOWERS WITH SCATTERED
STORMS AT SOME POINT TODAY. THE MAIN AREA OF RAIN EARLIER WAS THE
REMNANTS OF A 60 KNOT LOW LEVEL JET THAT MOVED OVER THE AREA VERY
EARLY THIS MORNING. ANOTHER SECONDARY WEAKER LOW LEVEL JET OF 35
KNOTS IS SUPPORTING THE SHOWERS EXITING THE SE CORNER OF THE AREA.
THE REMAINDER OF THE RAIN IS DISSIPATING AS WE SEE THE WAVE AND LOW
LEVEL JET FORCING MOVING OUT, AND WEAK SHORT WAVE RIDGING BUILDING
IN.
MOST AREAS WILL SEE LITTLE TO NO ADDITIONAL RAIN TONIGHT. THE
EXCEPTION TO THIS WILL BE AREAS ACROSS THE FAR SOUTHERN PORTION OF
THE AREA OVERNIGHT. THE SFC FRONT IS SINKING SOUTH, AND ANOTHER LOW
LEVEL JET WILL INTERSECT IT. THIS WILL EVEN BE A BIT WEAKER, BUT
JUST ENOUGH FORCING GIVEN THE DEEP MOISTURE IN PLACE. MU CAPES ARE
FORECAST TO INCREASE TO A FEW HUNDRED J/KG WITH THE ARRIVAL OF THE
LOW LEVEL JET. THIS INSTABILITY WILL BE ELEVATED, SO THE POTENTIAL
OF SEVERE WEATHER IS QUITE LIMITED.
ANOTHER LOW LEVEL JET WILL CLIP THE FAR SOUTHERN PORTION OF THE AREA
AGAIN WEDNESDAY NIGHT, BRING ADDITIONAL SHOWER/STORM CHANCES. THERE
WAS A FAIR AMOUNT OF DISAGREEMENT WITH RAIN PLACEMENT WEDNESDAY
NIGHT. A BETTER CONSENSUS HAS DEVELOPED, WITH THE NOSE OF THE LOW
LEVEL JET LIKELY ALONG I-94, AND BRINGING RAIN MOSTLY SOUTH OF I-96.
ONCE AGAIN, INSTABILITY WILL BE ELEVATED BEING FURTHER REMOVED FROM
THE SFC FRONT TO OUR SOUTH. SOME LOCALIZED HEAVY RAIN WILL BE THE
MAIN THREAT.
- COOLER AND DRIER WEATHER THURSDAY AND FRIDAY
ONCE THE LOW LEVEL JET WEDNESDAY NIGHT PASSES, THE FRONT WILL BE
DRIVEN FURTHER SOUTH AWAY FROM THE AREA. IN ADDITION, WE WILL BE
SEEING A STRONGER SYSTEM START TO BECOME ORGANIZED WELL WEST OF THE
AREA. THIS WILL TEMPORARILY STOP THE WEAK IMPULSES COMING THROUGH,
AND JUST ALLOWING SOME RIDGING TO RESIDE FOR A COUPLE OF DAYS. THE
LACK OF RAIN AND BREAKS IN THE CLOUDS WILL ALLOW FOR SOME SUN TO
WARM MAX TEMPS UP A COUPLE OF DEGREES COMPARED TO THE COOLER WEATHER
UNDER THE CLOUDS AND RAIN. TEMPERATURES WILL BE QUITE SEASONABLE
WITH HIGHS WELL INTO THE 70S, AND LOWS IN THE 50S.
- STRONGER SYSTEM WITH HEAVY RAIN POTENTIAL SATURDAY
THE BETTER ORGANIZED SYSTEM WILL START AFFECTING THE AREA LATE
FRIDAY WITH A STRENGTHENING FLOW AHEAD OF IT FROM THE SW. THE
ATMOSPHERE SHOULD SATURATE SUFFICIENTLY LATE FRIDAY NIGHT TO ALLOW
RAIN TO BEGIN TO REACH THE GROUND.
THE BEST CHANCE OF RAIN WILL COME CENTERED ON SATURDAY AS THE LOW
LEVEL JET AXIS NOSES OVER THE AREA IN A WEAKENING STATE. THE WARM
SECTOR OF THIS SYSTEM STAYS SOUTH OF THE AREA AS THE LOW MOVES
THROUGH THE HEART OF THE AREA. THE VAST MAJORITY OF THE INSTABILITY
WILL STAY SOUTH OF THE STATE BORDER. THERE MAY BE A CHANCE OF SOME
THUNDER ACROSS THE FAR SOUTHERN COUNTIES.
THE MOST LIKELY HIGHEST IMPACT WITH THIS SYSTEM WILL BE HEAVY RAIN
POTENTIAL. THE VAST AMOUNT OF MOISTURE THAT WILL BE ASSOCIATED WITH
THIS SYSTEM AND THE STRENGTH AND SLOW SPEED, WILL ALL FOR SOME
HEAVY RAIN AMOUNTS TO BE POSSIBLE. WPC HAS OUR AREA PLACED UNDER A
SLIGHT RISK FOR SATURDAY, WHICH WE AGREE WITH STRONGLY AT THIS TIME.
THINGS BECOME QUITE UNCERTAIN FOR SUNDAY AND BEYOND. WE WILL SEE THE
PATTERN RELOAD WITH AN UPPER LOW TO OUR WEST, BRINGING A DEEP SW
FLOW OVER THE AREA. THIS WILL EJECT SHORT WAVE TROUGHS AT TIMES, AND
INTERACT WITH HIGHER MOISTURE. THE QUESTION IS WHERE DOES THE MAIN
AXIS SET UP. IT IS TOO FAR TO PIN DOWN THOSE DETAILS AT THIS TIME,
SO WE WILL CONTINUE TO MONITOR THE TRENDS.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 146 PM EDT TUE SEP 15 2026
VICINITY THUNDERSTORMS ARE CLEARING AWAY FROM JXN, LEAVING SOME
AREAS OF RAIN AND A MIX OF SKY CONDITIONS AND FLIGHT CATEGORIES.
GENERALLY, MVFR CIGS WILL BE NEAR AND NORTH OF MKG AND GRR FOR THE
NEXT SEVERAL HOURS. AFTER 00 Z, CONDITIONS SHOULD IMPROVE IN THE
NORTHERN AREAS AND DETERIORATE IN SOUTHERN MICHIGAN, WITH A CHANCE
OF SHOWERS AND THUNDERSTORMS NEAR AZO, BTL, AND JXN.
MARINE
ISSUED AT 240 PM EDT TUE SEP 15 2026
THE GALES FROM EARLIER HAVE DIMINISHED, AND ARE QUICKLY DIMINISHING
MORE THIS AFTERNOON WITH THE PASSAGE OF THE FRONT. THE GRADIENT
BEHIND IT IS NOT SIGNIFICANT, SO WINDS WILL CONTINUE TO DROP. WAVES
WILL TAKE A BIT LONGER TO DROP BELOW 4 FT, BUT SHOULD AT ALL AREAS
BY LATER THIS EVENING.
THE NEXT COUPLE OF DAYS LOOK MUCH QUIETER WITH A MUCH WEAKER
GRADIENT EXPECTED WITH RIDGING NEARBY. THE NEXT PERIOD OF POTENTIAL
HEADLINES WILL BE STARTING ON FRIDAY AND LINGERING INTO SATURDAY
WITH A STRONG SYSTEM EXPECTED TO APPROACH AND MOVE THROUGH THE AREA.
GRR WATCHES/WARNINGS/ADVISORIES
MI...BEACH HAZARDS STATEMENT UNTIL 11 PM EDT THIS EVENING FOR MIZ037-
043-050-056.
BEACH HAZARDS STATEMENT UNTIL 5 PM EDT THIS AFTERNOON FOR MIZ064-
071.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EDT THIS AFTERNOON FOR LMZ844-
845.
SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR LMZ846>849.
DISCUSSION...NJJ
AVIATION...CAS
MARINE...NJJ
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