FXUS63 KGRR 090557
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
157 AM EDT Thu Jul 9 2026

.KEY MESSAGES...

- Slow moving front brings rain tonight and Thursday

- Upper High builds in early next week

&&

.DISCUSSION...
Issued at 258 PM EDT Wed Jul 8 2026

- Slow moving front brings rain tonight and Thursday

Thunderstorms ahead of the cold front have shown a weakening trend
last couple hours as they move over Lake Michigan and we do not
expect significant rain or thunder until closer to midnight as 
the front sags in from the northwest. 

Severe and excessive rainfall threats are low overnight as the 
front moves through with limited instability, shear and deep 
moisture, but the southern zones could see some resurgent
convection on Thursday morning. With deeper moisture pooling south
of the front, any training of thunderstorms could bring minor
flooding.

Showers could linger through Friday afternoon across the southern
zones as the front becomes parallel to the upper flow and slows
down or stalls.

- Upper High builds in early next week

Large scale subsidence and drying begins over the weeknight as an
upper high builds across the Northern Plains and edges into Lower
Michigan. Expect a spell of hot and dry weather for early next 
week before heights fall as an upper trough amplifies across 
eastern Canada.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 157 AM EDT Thu Jul 9 2026

Thunderstorm and rain vicinity and north of MKG is gradually
weakening and will probably only be a factor distant north of GRR
and LAN the next few hours. Expecting cloud bases mostly at or 
above 4,000 feet today. The big caveat to the prevailing VFR will
be scattered showers and thunderstorms developing during the day
and moving east. Went with a pretty long duration window of 
prob30 thunderstorm as models offer a wide variety of solutions 
regarding coverage and location of thunderstorms at a given time.
Any better-developed thunderstorm cells this afternoon, especially
east of GRR-AZO, will be capable of microbursts/LLWS and temporary
IFR visibility.

&&

.MARINE...
Issued at 258 PM EDT Wed Jul 8 2026

Scattered thunderstorms with gusty winds and heavy downpours will
be moving southeast across Lake Michigan tonight into Thursday 
morning. Otherwise, conditions will continue relatively tranquil
into the weekend. As high pressure builds in on Thursday into
Friday, north winds could gust to 20 knots, otherwise winds should
remain at 15 knots or less.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Ostuno
AVIATION...CAS
MARINE...Ostuno