580
FXUS63 KGRR 122312
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
712 PM EDT SAT SEP 12 2026
KEY MESSAGES
- ISOLATED SHOWERS THIS EVENING
- A FEW SHOWERS SUNDAY AFTERNOON
- UNSETTLED WEATHER TUESDAY AND BEYOND WITH RAIN CHANCES DAILY
DISCUSSION
ISSUED AT 156 PM EDT SAT SEP 12 2026
- ISOLATED SHOWERS THIS EVENING
SURFACE TEMPERATURES HAVE WARMED A BIT AND DEW POINTS HAVE
INCREASED A COUPLE OF NOTCHES AS COMPARED TO THE LAST COUPLE OF
DAYS. THIS IS EVIDENT IN THE SATELLITE IMAGERY WITH QUITE A BIT
MORE CUMULUS DEVELOPMENT OVER THE AREA TODAY AWAY FROM LAKE
MICHIGAN. THIS IS DUE TO THE INCREASED FLOW AHEAD OF THE COLD
FRONT THAT IS OVER CENTRAL WISCONSIN AS OF JUST BEFORE 2 PM.
EVEN THOUGH THE SFC IS SEEING A BIT OF MOISTURE AHEAD OF THE
FRONT, THE COLUMN AS A WHOLE IS RELATIVELY DRY WITH A LACK OF A
GOOD FEED OF DEEP MOISTURE PRESENT. IN ADDITION, THE UPPER WAVE
SUPPORTING THE FRONT REMAINS OVER SOUTHERN ONTARIO, WITH LITTLE TO
NO DEEP FORCING DOWN THIS WAY. THIS CONTINUES THE MAINLY DRY
FORECAST WITH ABOUT A 10% CHANCE OF SOMETHING POPPING UP WITH THE
FRONT LATE THIS AFTERNOON AND EVENING.
- A FEW SHOWERS SUNDAY AFTERNOON
THE FIRST HALF OF SUNDAY WILL BE DRY WITH COOLER AIR COMING IN
BEHIND THE DEPARTING COLD FRONT. WE WILL SEE ANOTHER CHANCE OF
RAIN DEVELOP SUNDAY AFTERNOON, OVER MAINLY THE SOUTHERN PORTION OF
THE FORECAST AREA.
THE FEATURE RESPONSIBLE FOR THIS CHANCE OF RAIN IS ANOTHER UPPER
LEVEL SHORT WAVE THAT DIGS A BIT FURTHER SE THAN THE ONE
RESPONSIBLE FOR TODAY'S FRONT. THE FORCING WITH THIS WAVE, ALONG
WITH THE CONVERGENCE AND LIMITED MOISTURE POOLING ALONG THE SFC
FRONT WILL PROVIDE FOR A BAND OR TWO OF SHOWERS SUNDAY AFTERNOON
WITH DIURNAL HEATING. LIMITED LOW LEVEL MOISTURE AND TEMPS WILL
KEEP THUNDER FROM BEING POSSIBLE AS SFC BASED AND ELEVATED LI'S
ARE WELL ABOVE ZERO C, AND MU CAPE IS ZERO.
THIS SHOULD MOVE SOUTH OF THE AREA BY 00Z MONDAY, AND ALLOW SFC
RIDGING TO BUILD OVERHEAD FOR SUNDAY NIGHT AND MOST OF MONDAY. THE
AIR MASS WILL BE NOTICEABLE COOLER BEHIND THE SUNDAY FRONT.
- UNSETTLED WEATHER TUESDAY AND BEYOND WITH RAIN CHANCES DAILY
SSW FLOW AT THE SFC AND ALOFT WILL INCREASE QUICKLY LATE MONDAY
NIGHT ON THE BACK SIDE OF THE SFC RIDGE, AND AHEAD OF THE NEXT
SYSTEM. THIS SYSTEM IS CURRENTLY AN UPPER LOW JUST OFF OF THE
PACIFIC NORTHWEST. THIS SYSTEM WILL ROTATE EASTWARD AND EVENTUALLY
NORTHEAST BY TUESDAY.
THE WARM FRONT WILL MOVE THROUGH MONDAY EVENING, WITH LITTLE TO
NO PRECIPITATION FOR OUR AREA THROUGH THE DAYLIGHT HOURS, AS THE
LOW LEVEL JET AND MOISTURE AXIS STAYS WELL WEST OF THE AREA. THE
LOW LEVEL JET MOVES OVERHEAD ON TUESDAY AHEAD OF THE FRONT, BUT
MUCH OF THE SHOWERS/STORMS WILL STAY NORTH OF THE AREA. WE WILL
SEE SOME RAIN CHANCES ON TUESDAY, BUT MUCH OF THE ACTIVITY WILL
STAY NW.
THE COLD FRONT IS FORECAST TO STALL OUT, JUST AS IT PASSES SOUTH
OF THE FORECAST AREA TUESDAY NIGHT. IT BECOMES PARALLEL TO THE
UPPER FLOW WITH THE MAIN ENERGY DRIVING NE INTO CANADA.
THE REST OF THE FORECAST PERIOD THROUGH NEXT SATURDAY WILL BE
FOCUSED ON THE STALLED OUT FRONT NEAR THE AREA. WE WILL SEE SHORT
WAVE ACTIVITY RIDE ALONG THE UPPER FLOW FROM THE WSW, AND INITIATE
ROUNDS OF SHOWERS AND STORMS. THE EXACT PLACEMENT OF THE FRONT AT
ANY TIME IS QUITE UNCERTAIN, AND THUS THE RAIN CHANCES WILL BE
ALSO. THE FRONT WILL BE CLOSE ENOUGH THROUGH THE ENTIRE PERIOD AT
THIS TIME TO JUSTIFY CHC POPS RIGHT ON THROUGH NEXT SATURDAY.
AVIATION /00Z TAFS THROUGH 00Z MONDAY/
ISSUED AT 712 PM EDT SAT SEP 12 2026
A BANK OF CLOUDS AROUND 3,500 TO 4,500 FEET IS COMING IN TO MKG
AND WILL PROGRESS EASTWARD THROUGH THE REST OF THE AREA DURING THE
NIGHT. THIS SHOULD CLEAR OUT PRIOR TO DAYBREAK SUNDAY. THIS
CLEARING COULD ALLOW SOME PATCHY FOG TO FORM BETWEEN 08 TO 13 Z,
WHICH THE CONSENSUS OF SHORT-TERM MODELS IS ANGLING FOR ESPECIALLY
AT LAN AND JXN.
MARINE
ISSUED AT 156 PM EDT SAT SEP 12 2026
WE ARE COMING TO THE END OF THE CURRENT SMALL CRAFT ADVISORY /
BEACH HAZARDS EVENT, AND WILL START TO ADDRESS THE NEXT EVENT FOR
SUNDAY.
WAVES NEAR AND NORTH OF LITTLE SABLE PT ARE LIKELY STILL JUST
HIGH ENOUGH TO NEED TO KEEP THE HEADLINES FOR NOW. THE
OBSERVATIONS NEAR KMKG SHOWS THAT THE HEADLINES FOR THAT AREA CAN
BE CANCELLED A BIT EARLY. THE WAVES FOR THE FAR NORTH WILL COME
DOWN THROUGH THIS EVENING, AND CAN BE CANCELLED OR EXPIRED.
WE WILL SEE THE WINDS AND WAVES PICK UP ONCE AGAIN LATER TONIGHT,
AND MORE SO SUNDAY AFTERNOON. WAVES MIGHT COME CLOSE TO CRITERIA
OVERNIGHT, BUT WILL BE SOLID ON SUNDAY WITH COLDER AIR COMING IN
BEHIND TONIGHT'S FRONT.
GRR WATCHES/WARNINGS/ADVISORIES
MI...BEACH HAZARDS STATEMENT UNTIL 8 PM EDT THIS EVENING FOR MIZ037-
043.
BEACH HAZARDS STATEMENT FROM SUNDAY MORNING THROUGH SUNDAY
EVENING FOR MIZ050-056-064-071.
MARINE...SMALL CRAFT ADVISORY FROM 11 AM TO 11 PM EDT SUNDAY FOR
LMZ844>847.
SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR LMZ848-849.
DISCUSSION...NJJ
AVIATION...CAS
MARINE...NJJ
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