397
FXUS63 KGRR 161133
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
733 AM EDT SUN AUG 16 2026
KEY MESSAGES
- SCATTERED SHOWERS AND STORMS TODAY
- SHOWER/STORM CHANCES LATE TUE TO EARLY WED, AND LATE WEEK
DISCUSSION
ISSUED AT 321 AM EDT SUN AUG 16 2026
- SCATTERED SHOWERS AND STORMS TODAY
SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED IN THE VICINITY
OF AN MCV MOVING FROM NORTHERN ILLINOIS TO SOUTHERN MICHIGAN THIS
MORNING, THEN AHEAD OF A WEAK COLD FRONT SWEEPING THROUGH THE
STATE THIS AFTERNOON. CAPE VALUES 500-1000 J/KG ARE CONFINED
MAINLY SOUTH OF I-96 THIS MORNING, THOUGH MAY EXTEND FARTHER
NORTH FOR A TIME AROUND MID DAY. STORM CELLS SHOULD BE FAIRLY
LIMITED IN ORGANIZATION GIVEN ABOUT 20 KNOTS OF 0-6 KM SHEAR. PW
AROUND 2 INCHES WILL MAKE FOR EFFICIENT RAINFALL RATES, THOUGH
LIMITED UPDRAFT WIDTH AND SCATTERED COVERAGE OF CELLS WOULD FAVOR
JUST ISOLATED SPOTS OF 1-2 INCH TOTALS, HIGHEST PROBABILITY SOUTH
OF I-96 PER THE HREF.
- SHOWER/STORM CHANCES LATE TUE TO EARLY WED, AND LATE WEEK
MONDAY WILL BRING RELIEF FROM THE HUMIDITY, AS DEW POINTS DROP TO
AROUND OR BELOW 60. SOME MOISTURE AND SLIGHTLY WARMER AIR FROM THE
CENTRAL CONUS RETURNS ON TUESDAY, AHEAD OF A COLD FRONT THAT WILL
SAG THROUGH ON WEDNESDAY, NUDGED SOUTH AS AN UPPER-LEVEL LOW
LUMBERS ACROSS HUDSON BAY AND NORTHERN ONTARIO. SCATTERED
THUNDERSTORMS ARE AGAIN POSSIBLE IN THE VICINITY OF THIS FRONT
MAINLY BETWEEN TUE EVENING AND EARLY WED MORNING, AS A MAJORITY
OF ENS AND GEFS MEMBERS INDICATE. INSTABILITY IS STILL A LITTLE IN
QUESTION, AS MOST SOLUTIONS PROJECT FAIRLY MODEST AMOUNTS IN THE
BALLPARK OF 500-1000 J/KG, THOUGH A FEW OFFER CLOSER TO 2000 J/KG.
THIS WOULD BE SOMETHING TO MONITOR FOR A MARGINAL SEVERE THREAT,
AS DEEP-LAYER SHEAR WILL BE GREATER THAN IT IS TODAY.
A MAJORITY OF ENSEMBLE MEMBER SOLUTIONS FAVOR DRIER AND SOMEWHAT
COOLER AIR FOR LATER WED INTO THURSDAY, FOLLOWED BY ANOTHER MODEST
MOISTURE RETURN LATE FRIDAY INTO SATURDAY WITH A CHANCE FOR MORE
SCATTERED SHOWERS OR STORMS. NATURALLY, THIS IS LOWER CONFIDENCE
THIS FAR OUT, GIVEN THE INCREASING SPREAD IN THE SOLUTION
ENVELOPE.
AVIATION /12Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 733 AM EDT SUN AUG 16 2026
SCATTERED THUNDERSTORMS NEAR GRR AND POTENTIALLY SOON IN VICINITY
OF AZO, BTL, JXN, AND LAN OVER THE NEXT 3 HOURS AS THE CELLS MOVE
EAST. MAIN HAZARDS ARE TEMPORARY IFR WITH HEAVY RAIN, AND
LIGHTNING. MICROBURST POTENTIAL IS FAIRLY LOW THIS MORNING, BUT IF
ANY ADDITIONAL CELLS DEVELOP LATER THIS MORNING AFTER 15 Z THROUGH
ABOUT 18 Z, IT'S POSSIBLE THERE COULD BE ISOLATED SURFACE GUSTS TO
30 KNOTS. IFR CEILINGS THIS MORNING TREND MVFR THIS AFTERNOON THEN
MOSTLY VFR BY EVENING.
MARINE
ISSUED AT 321 AM EDT SUN AUG 16 2026
SOUTHWEST WINDS BECOME WEST TODAY THEN NORTH TONIGHT. A FEW
THUNDERSTORM CELLS ARE POSSIBLE OVER LAKE MICHIGAN THIS MORNING,
MAINLY AN OCCASIONAL LIGHTNING THREAT. WAVES WILL BE 1 TO 2 FEET
WITH A LOW SWIM RISK TODAY. THE NORTH WINDS SHOULD KICK UP 2 TO 3
FOOT WAVES TONIGHT. A LOW SWIM RISK IS EXPECTED MONDAY, THEN A
MODERATE SWIM RISK TUESDAY WITH SOUTHWEST WINDS.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...CAS
AVIATION...CAS
MARINE...CAS
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