064
FXUS63 KGRR 041919
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
319 PM EDT FRI SEP 4 2026
KEY MESSAGES
- SHOWERS AND THUNDERSTORMS THIS EVENING
- DRYING OUT AND COOLING OFF THIS WEEKEND
- RAIN POSSIBLE TUESDAY
DISCUSSION
ISSUED AT 318 PM EDT FRI SEP 4 2026
- SHOWERS AND THUNDERSTORMS THIS EVENING
THE RADAR THIS AFTERNOON SHOWS SCATTERED THUNDERSTORMS IN AN AREA
OF ISENTROPIC ASCENT ALONG AND MOISTURE ADVECTION FROM SOUTHERN
WISCONSIN INTO SOUTHWEST LOWER MICHIGAN. THE CONVECTIVE-ALLOWING
MODELS SUCH AS THE HI-RES ARW AND FV3 SHOW THE STORMS ACROSS
SOUTHERN WISCONSIN MOVING EAST-SOUTHEAST THIS EVENING AND
TRAVERSING THE SOUTHERN HALF OF THE FORECAST AREA. THIS IS
REFLECTED IN THE FORECAST, ALTHOUGH TWEAKS MAY BE NEEDED OF COURSE
THANKS TO THE INHERENT UNCERTAINTY IN MODELING CONVECTION THAT WE
HAVE SEEN THE PAST SEVERAL DAYS.
- DRYING OUT AND COOLING OFF THIS WEEKEND
A DEVELOPING OMEGA BLOCK ACROSS THE CONUS THIS WEEKEND RESULTS AS
THE CENTRAL U.S. HEAT DOME IS BOOKENDED BY CUT OFF LOWS ACROSS
THE NE AND NW CONUS. THIS LOWERS HEIGHTS ACROSS THE CENTRAL GREAT
LAKES AND ALLOWS SURFACE HIGH PRESSURE TO BUILD IN FROM THE
NORTHEAST WITH LOWER TEMPERATURES AND DEW POINTS AND A VERY FINE
LABOR DAY WEEKEND FROM SATURDAY THROUGH MONDAY. IN FACE, MORNING
LOWS ON SUNDAY AND MONDAY COULD BE IN THE UPPER 40S TO LOWER 50S
ACROSS THE NORTHERN HALF OF THE FORECAST AREA.
- RAIN POSSIBLE TUESDAY INTO WEDNESDAY
THE SURFACE HIGH RETREATS EAST EASTWARD BY TUESDAY AS THE OMEGA
BLOCK BREAKS DOWN. THE LOW ACROSS THE PACIFIC NW KICKS EAST AND
FLATTENS THE UPPER HIGH, WITH SURFACE LOW PRESSURE TRACKING ACROSS
THE NORTHERN GREAT LAKES. RETURN FLOW OF MOISTURE AND A SURFACE
WARM FRONT SHOULD KICK OFF SOME SHOWERS AND THUNDERSTORMS LATE
TUESDAY INTO WEDNESDAY. ANOTHER ROUND OF STORMS WILL BE POSSIBLE
AS A COLD FRONT MOVES THROUGH LATE WEDNESDAY.
AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 210 PM EDT FRI SEP 4 2026
WITH THIS MORNING'S THUNDERSTORM COMPLEXES OUT OF THE PICTURE, THE
FLIGHT CATEGORIES ARE MOSTLY IMPROVING TO VFR, EXCEPT FOR MVFR
CEILINGS EXPECTED TO HANG ON AROUND MOUNT PLEASANT (MOP), AND
PERHAPS A PATCH OR TWO OF CLOUDS BETWEEN 500 AND 2,000 FEET
DEVELOPING OVER THE NEXT HOUR OR SO ELSEWHERE.
TONIGHT WILL LIKELY BRING WORSENING CEILINGS OR VISIBILITY
SPREADING SOUTHWEST INTO THE TAF SITES FROM THAT SAME MOUNT
PLEASANT CLOUD DECK, BECOMING IFR AT SOME POINT LATE TONIGHT
(AFTER APPROX 03 TO 06 Z) THEN IMPROVING TO MVFR AFTER 13 Z. ALSO,
LINGERING INSTABILITY AND MOISTURE/CLOUDS AT OR ABOVE 4,000 FEET
IN SOUTHWEST MICHIGAN MAY DEVELOP SCATTERED THUNDERSTORMS NEAR
MKG, AZO, AND BTL BETWEEN 01 AND 08 Z.
MARINE
ISSUED AT 318 PM EDT FRI SEP 4 2026
SHOWERS AND THUNDERSTORMS COULD BRING BRIEF HEAVY RAIN AND GUSTY
WINDS FROM GRAND HAVEN TO SOUTH HAVEN THIS EVENING, THEN FAIR
WEATHER WITH LIGHT OFFSHORE WINDS, GENERALLY LESS THAN 15 KNOTS,
CAN BE EXPECTED FOR SATURDAY THROUGH MONDAY. HIGH PRESSURE WILL
MOVE EAST ON TUESDAY AND WINDS WILL BE ON THE INCREASE, WITH A
SMALL CRAFT ADVISORY POSSIBLE.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...OSTUNO
AVIATION...CAS
MARINE...OSTUNO
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