372
FXUS63 KGRR 102258
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
658 PM EDT MON AUG 10 2026
KEY MESSAGES
- UNSETTLED WITH SEVERAL CHANCES OF SHOWERS AND THUNDERSTORMS
THROUGH THURSDAY
- MORE WIDESPREAD RAINFALL POTENTIAL THIS WEEKEND
DISCUSSION
ISSUED AT 144 PM EDT MON AUG 10 2026
- UNSETTLED WITH SEVERAL CHANCES OF SHOWERS AND THUNDERSTORMS
THROUGH THURSDAY
PERSISTENT WEST-NORTHWEST FLOW WITH SEVERAL EMBEDDED SHORTWAVES WILL
KEEP A FRONTAL BOUNDARY STALLED SOUTH OF THE AREA OVER THE NEXT
SEVERAL DAYS. EACH SHORTWAVE WILL DRIVE THE POTENTIAL FOR SHOWERS
AND THUNDERSTORMS UNTIL LATE THURSDAY INTO FRIDAY A PATTERN SHIFT
FORCES THE FRONT SOUTH.
FIRST CHANCE IS THIS AFTERNOON WHERE THE NAMNEST, WHICH IS BEST
HANDLING ONGOING CONVECTION, SUGGESTS AN ISOLATED POP-UP
THUNDERSTORM OR TWO. COVERAGE GIVEN LITTLE MESOSCALE FORCING WILL BE
WIDELY ISOLATED WITH MANY IF NOT ALL STAYING DRY.
NEXT CHANCE ARRIVES TONIGHT WITH THE LOW-LEVEL JET JUST SOUTH OF THE
AREA. THIS FOCUSES THE BEST CONVECTIVE POTENTIAL SOUTH OF THE AREA,
THOUGH A FEW SHOWERS AND STORMS ARE POSSIBLE CLOSER TO THE FRONT
ALONG AND SOUTH OF THE I-94 CORRIDOR.
ATTENTION THEN TURNS TO TUESDAY AFTERNOON WHERE A COMPLEX OF STORMS
IS FORECAST TO EITHER JUST MISS US TO THE SOUTH, OR IMPACT OUR
SOUTHWEST FORECAST AREA. BEST CHANCE IF IT DOES REACH US IS SOUTH OF
A GRAND HAVEN TO LANSING LINE. WITH AMPLE DEEP LAYER SHEAR (40+
KTS) AND MUCAPE VALUES NORTH OF 2000 J/KG, THIS COMPLEX MAY HAVE
THE POTENTIAL FOR DAMAGING WINDS IF IT IMPACTS OUR FORECAST AREA.
THIS MATCHES THE SIGNAL SEEN IN SEVERAL DIFFERENT MACHINE LEARNING
GUIDANCE TOOLS. HOWEVER, STORM TRACK DEPENDS HIGHLY ON HOW STORMS
EVOLVE TONIGHT SO CONFIDENCE IN ANY SEVERE WEATHER THREAT IS LOW.
WEDNESDAY AND THURSDAY WILL FEATURE ADDITIONAL AFTERNOON/EVENING
THUNDERSTORM CHANCES AS WEAK SHORTWAVES INTERACT WITH THE FRONT
SOUTH OF THE AREA. BEST CHANCE WILL BE SOUTH OF I-96, PARTICULARLY
NEAR I-94. THE FRONT THEN IS DRIVEN SOUTH FRIDAY ENDING THE
UNSETTLED PATTERN BRIEFLY. THERE ALSO MAY BE LOCALLY HEAVY RAIN
WITH ANY OF THESE ROUNDS, WITH ISOLATED MAXIMUM TOTALS AOA 2
INCHES SHOWN IN HREF/REFS LPMM GUIDANCE.
- MORE WIDESPREAD RAINFALL POTENTIAL THIS WEEKEND
FRIDAY LOOKS TO BE DRY AS SURFACE AND UPPER-LEVEL RIDGING
SUPPRESSES CONVECTIVE POTENTIAL. HOWEVER, THAT PATTERN CHANGES BY
SATURDAY. THIS WEEKEND, POTENTIALLY AS EARLY AS FRIDAY NIGHT, A
MID-LEVEL WAVE EJECTS INTO THE CENTRAL GREAT LAKES DRIVING A
SURFACE LOW ACROSS THE AREA. THIS WILL BRING MORE WIDESPREAD
PRECIPITATION UNTIL THE LOW EXITS LATE WEEKEND WITH COOLER
TEMPERATURES WITH IT.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 144 PM EDT MON AUG 10 2026
DAYTIME HEATING, COUPLED WITH A MOIST BOUNDARY LAYER AIDED BY OVERNIGHT
RAINFALL, HAS RESULTED IN A SC CLOUD DECK WITH MVFR CEILINGS /AROUND
2KFT/ AT ALL TAF SITES. WITH CONTINUED WARMING THIS AFTERNOON, EXPECT
SC TO LIFT TO VFR CU DECK /AROUND 3.5 KFT/ AFTER 19-20Z. STATIONARY
FRONT OVER THE LOWER GREAT LAKES WILL CONTINUE TO SERVE AS FOCAL FOR
SCATTERED STORMS NEXT 24 HR, WITH THE NEXT ROUND OF THUNDERSTORMS
POTENTIALLY MOVING INTO SW LOWER /INCLUDING THE AZO-BTL TAF SITES/
AFTER 02-03Z THIS EVENING. YET ANOTHER ROUND OF STORMS MAY BE
APPROACHING AZO/BTL/GRR AFTER 16Z TUESDAY, BUT WILL NOT INCLUDE IN
TAFS AT THIS TIME.
OTHERWISE, EXPECT SCT-BKN MID CLOUDS TONIGHT NORTH OF THE BOUNDARY,
ALONG WITH 2-4SM VSBYS IN FOG AFTER 06-07Z. WINDS WILL REMAIN LIGHT
THROUGHOUT TAF PERIOD, WITH WESTERLY FLOW BECOMING VARIABLE
TONIGHT.
AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 658 PM EDT MON AUG 10 2026
MVFR CIGS HAVE MOSTLY SCATTERED OUT WITH MAINLY MID AND HIGH
CLOUDS. FOR THE MOST PART, THAT WILL PERSIST THROUGH THE EVENING.
THE MAIN CAVEAT IS LATE THIS EVENING THROUGH AROUND 07Z, SCATTERED
THUNDERSTORMS MAY DEVELOP ALONG A FRONT THAT MAY IMPACT AZO/BTL.
THEN, MOSTLY CLEAR SKIES AND LIGHT WINDS ATOP A MOIST BOUNDARY
LAYER WILL ALLOW 2-4SM FOG TO DEVELOP OVERNIGHT, AND POTENTIALLY
SOME LOW STRATUS AS WELL. CAN'T RULE OUT (10% CHANCE) OF SUB 2SM
VISBYS. FOG WILL DISSIPATE MID TO LATE TUESDAY MORNING. THEN, A
LINE OF THUNDERSTORMS IS FORECAST TO TRACK THROUGH THE REGION FROM
THE WEST. CONFIDENCE IS LOW IN WHERE IT TRACKS, WITH A VERY REAL
CHANCE IT TRACKS SOUTH OF THE TERMINALS. HAVE GONE PROB30 TSRA FOR
AZO/BTL/JXN WHERE CONFIDENCE IS HIGHER IN THUNDER POTENTIAL AND
SHOWERS FOR THE OTHER SITES WHERE CONFIDENCE IS LOWER. 17-13Z IS
THE MAIN WINDOW OF CONCERN, AND TIMING AND CONFIDENCE WILL BE
REFINED AS UPSTREAM TRENDS BECOME CLEAR.
MARINE
ISSUED AT 144 PM EDT MON AUG 10 2026
CONDITIONS LOOK TO REMAIN BELOW SMALL CRAFT ADVISORY/BEACH HAZARDS
STATEMENT LEVELS MUCH OF THE WEEK GIVEN WEAK GRADIENT FLOW ACROSS
THE AREA. THE ONE CAVEAT IS THAT ONE OR MORE ROUNDS OF
THUNDERSTORMS ARE LIKELY BETWEEN TONIGHT AND THURSDAY ACROSS THE
WATERS. LOCALLY HIGHER WINDS AND WAVES ARE POSSIBLE IN ANY
THUNDERSTORMS OR AS A RESULT OF THEIR OUTFLOW WINDS EVEN IF THEY
MISS OUR PART OF THE LAKE. MARINE HEADLINES MAY BE NEEDED FRIDAY
NIGHT INTO THE WEEKEND AS A MORE ROBUST SYSTEM CROSSES THE CENTRAL
GREAT LAKES.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...THOMAS
AVIATION...THOMAS
MARINE...THOMAS
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