108
FXUS63 KGRR 121850
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
250 PM EDT WED AUG 12 2026
KEY MESSAGES
- CHANCE FOR ISOLATED THUNDERSTORMS THIS AFTERNOON AND EVENING
- FOGGY AND CHANCES FOR LIGHT RAINFALL THROUGH THE SOUTH TO END THE WORK WEEK
- PRECIPITATION CHANCES THIS WEEKEND
DISCUSSION
ISSUED AT 234 PM EDT WED AUG 12 2026
- CHANCE FOR ISOLATED THUNDERSTORMS THIS AFTERNOON AND EVENING
LOW STRATOCU CONTINUES TO REMAIN THROUGH THE SOUTHERN TIER OF
MICHIGAN WITH LIGHT SOUTHERLY WINDS. SEVERE WEATHER THROUGH
INDIANACONTINUES TO TRACK TO THE SOUTH EAST WITH ANY OUTFLOW
MOVING NORTHWARD RUNNING INTO A WALL OF STABILITY. THAT STABILITY
WILL STIFLE ANY CONVECTION THIS AFTERNOON AND EVENING THROUGH
SOUTHERN MICHIGAN. THE SOLE CAVEAT WILL BE CONVECTION FROM
BOUNDARY INTERACTIONS. CURRENTLY THERE IS THREE DIFFERENT OUTFLOW
BOUNDARIES MOVING IN DIFFERENT DIRECTIONS THAT ARE SET TO
INTERSECT THROUGH SOUTHWEST MI. THERE ARE SOME CAMS THAT SUGGEST
THAT SOME CONVECTION COULD FORM. SFC BASED CAPE IS AROUND 1000
J/KG ALONG THE I 94 CORRIDOR. HOWEVER, THERE IS UPWARDS OF 200
J/KG OF CIN. SO WHILE IT IS POSSIBLE THAT CONVECTION COULD FORM
THROUGH THE SOUTH AND WILL NEED TO BE WATCHED, THE STABLE AIR
COULD PRECLUDE STORM DEVELOPMENT.
THE BETTER CHANCE WILL BE AS A SPEED MAX MOVES FROM THE EAST TO SOUTHEAST ACROSS
CENTRAL LOWER MI. LAPSE RATES IN THE TRI CITY AREA ARE 6 TO 7 C/KM
THROUGH THE MID LEVELS. COUPLE THAT WITH MU CAPE AROUND 1400 J/KG AND PWATS OF 1.43
INCHES AND YOU HAVE A DECENT ENVIRONMENT FOR STORM DEVELOPMENT.
THERE IS SOME CU DEVELOPMENT THROUGH CENTRAL AND NORTHER LOWER.
HOWEVER, A LARGE CIRRUS SHIELD SHOULD LIMIT DAYTIME HEATING,
THOUGH MAX TEMPS ALONG THE US 10 CORRIDOR COULD GET INTO THE MID
80S. LATEST CAMS CONTINUE TO SUGGEST THE POTENTIAL FOR ISOLATED
STORMS TO BE POSSIBLE AFTER 20Z. DCAPES ARE IN THE 800 TO 900 J/KG
RANGE SO DAMAGING WINDS ARE THE MAIN CONCERN. ANY SHOWER AND
STORM CHANCES WILL DWINDLE THROUGH THE EVENING HOURS,
- FOGGY AND CHANCES FOR LIGHT RAINFALL THROUGH THE SOUTH TO END THE WORK WEEK
ANY RAINFALL AND CONVECTION WILL ADD TO THE MOISTURE THROUGHOUT THE LOWER
LEVELS THROUGH SOUTHERN MICHIGAN. CALM WINDS, A STABLE AIR MASS AND MOIST
LOWER LEVELS IS A GREAT RECIPE FOR ANOTHER ROUND OF FOG THROUGH THURSDAY MORNING.
EXPECT AREAS OF FOG TO DEVELOP OVERNIGHT. FOG COULD BE DENSER THAN THIS MORNING'S
BUT WILL HOLD OFF ON ANY ADVISORIES FOR NOW.
ANOTHER UPPER LEVEL TROUGH WILL DROP DOWN FROM THE WEST
TOMORROW. THE TRACK OF THAT TROUGH IS TRENDING TOWARDS THIS WEEK'S
PREVIOUS SYSTEMS. THEY ARE TRENDING TOWARDS IN SOUTH INTO OHIO.
THE ONLY PRECIPITATION COULD BE ON THE FRINGES ALONG THE I 94
CORRIDOR. ONLY LIGHT RAIN IS EXPECTED WITH A LOW CHANCE FOR ANY
THUNDER.
- PRECIPITATION CHANCES THIS WEEKEND
THE NEXT CHANCE FOR WIDESPREAD PRECIPITATION WILL BE SATURDAY
NIGHT AND SUNDAY AS THE PATTERN SHIFTS AND THE ZONAL FLOW SHIFTS
NORTHWARD BRINGING A MID LEVEL SHORTWAVE PROPAGATES OVER HIGH
PRESSURE BUILDING INTO THE GREAT PLAINS.
THAT SHOT WAVE WILL BRING DECENT SURGE OF MOISTURE SUNDAY.
THERE IS SOME QUESTION ON TIMING AN POSITION OF THE MID LEVEL
TROUGH. HOWEVER THERE SHOULD BE GOOD THICKNESS ADVECTION WITH
MUCAPE VALUES IN EXCESS OF 2000 J/KG. SO THERE IS THE PERSISTENT
TREND FOR THE POTENTIAL FOR STRONGER STORMS. MID TO LONG RANGE
MODELS ALSO CONTINUE TO SHOW A 35 TO 40 KT 850MB JET THROUGH LOWER
MICHIGAN SUNDAY MORNING. THIS WILL AID STORM DEVELOPMENT SUNDAY.
AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 150 PM EDT WED AUG 12 2026
A SOMEWHAT COMPLEX AVIATION FORECAST FOR SOUTHWEST MICHIGAN. LOW
LEVEL MOISTURE ADVECTION INTO THE I-94 CORRIDOR /NORTH OF INDIANA
CONVECTION/ IS CONTINUING TO SUPPORT STUBBORN /IFR/ LOW CLOUDS
AND REDUCED VSBYS AT AZO/BTL/JXN. MODELS SUPPORT IMPROVING
CONDITIONS BY LATE AFTERNOON, BUT THIS PROCESS MAY BE SLOWED GIVEN
MID/UPPER CLOUDS AND LACK OF DRIER AIR NEAR SURFACE. TAFS REFLECT
IMPROVING CONDITIONS TO VFR AT AZO/BTL/JXN AFTER 20Z, BUT THIS
COULD EASILY BE DELAYED. IN FACT, WILL NEED TO MONITOR SOME OF
THESE LOWER CLOUDS POSSIBLY REACHING LAN NEXT 1-2 HR.
ELSEWHERE, INCLUDING MKG/GRR/LAN, A SMATTERING OF CU/SC AND SCT-
BKN AC/CI IS BEING OBSERVED, BUT VFR CONDITIONS PREVAIL. EXPECT
LOW CLOUDS AND FOG TO REFORM AFTER 05Z AND CONTINUE THROUGH
DAYBREAK. THEN, VFR WEATHER WILL RETURN AFTER ROUGHLY 13Z WITH
MAINLY HIGH CLOUDS EXPECTED.
WINDS WILL REMAIN LIGHT AND VARIABLE THROUGH TONIGHT, THEN BECOME
E/SE UNDER 10KT ON THURSDAY.
MARINE
ISSUED AT 247 PM EDT WED AUG 12 2026
NOT EXPECTING MUCH WINDS AND WAVES OVER THE NEXT FEW DAYS.
THE MAIN CONCERNS WILL BE THE POTENTIAL FOR MARINE FOG AND ANY
THUNDERSTORMS MOVING FROM THE WEST IN THE AFTERNOONS. FOG WILL
REMAIN A THREAT OVER THE WATER UNTIL DRIER DEW POINTS MOVE INTO
THE REGION. THAT DOES NOT REALLY HAPPEN THIS WEEK SO THE THREAT OF
FOG WILL CONTINUE THROUGH THE REST OF THE WEEK.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...CERU
AVIATION...SMITH
MARINE...CERU
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