544
FXUS63 KGRR 150604
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
204 AM EDT Tue Sep 15 2026

.KEY MESSAGES...

- Showers And Storms Tuesday

- Several additional chances of showers and storms this week.

&&

.DISCUSSION...
Issued at 203 AM EDT Tue Sep 15 2026

- Showers And Storms Tuesday

The first round of showers is ongoing across Central and Northern
Michigan associated with a 925-850mb FGEN axis across the Central
Great Lakes. This is area is expected to propagate southeast with
time across the area. Could be some heavy rainfall, however with
timing near diurnal minimum and associated poor instability severe
weather is unlikely.

The next round tracks through this afternoon and evening with
development ahead of a cold front. Given robust cloud cover and
precipitation as the front slides south, latest trends suggest
marginal instability will be in place here with better
destabilization south. However, there may be just enough surface
based instability, enhanced shear from the westerly flow, and PWATs
aoa 2" to support a wet microburst threat south of I94.

- Several additional chances of showers and storms this week.

We shift into a lower predictability pattern going into mid to late
week as predominantly zonal flow takes over. Right now the front
looks to stall south of us, but a northward shift enhances the risk
for several rounds of rainfall over the coming days. The exact
coverage/timing will be dependent on small perturbations in the large
scale flow regime. Given continuing high PWATs in place across the
area, periods of heavy rainfall are possible. The inverse is also
true. Some solutions like the 15/00z GFS keep the front more
southerly which would keep things drier. We then see another system
arrive late Friday into the weekend bringing the potential for
another round of showers and storms.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 111 AM EDT Tue Sep 15 2026

Latest trends suggest showers and thunderstorms will largely stay
north of the terminals through 09z before drifting south. MVFR
and lower conditions are possible in any showers and isolated
thunderstorms. Ahead of thunderstorms a period of LLWS is expected
with winds around 45 kts at 2kft. Showers/storms will clear this
afternoon from north to south. VFR is then expected this
afternoon/evening before patchy fog/rain may cause conditions to
deteriorate this evening. Given low confidence with this part of
the forecast being at the end of the window have kept this out of
the TAFs with the 06z package.

&&

.MARINE...
Issued at 203 AM EDT Tue Sep 15 2026

Marine observations show winds increasing in southerly flow as
expected, with the threat for gusts to gales peaking in the coming
hours near and north of Holland. A Gale Warning remains in effect
through daybreak, with a Small Craft Advisory needed on the backend
for continuing winds and waves. South of Holland winds should be
just a tad lower warranting an advisory. Conditions hazardous to
small craft continue into tonight before subsiding, with areas north
of Holland taking the longest to see waves diminish. A Beach Hazards
Statement is in effect for all lakeshore counties as dangerous waves
and currents, as high as 12 ft north of Holland, are expected. In
addition, isolated thunderstorms are expected over the waters
through mid-day.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through this evening for MIZ037-043-050-
     056.
     Beach Hazards Statement through this afternoon for MIZ064-071.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for LMZ844-
     845.
     Gale Warning until 8 AM EDT this morning for LMZ846>849.

&&

$$

DISCUSSION...Thomas
AVIATION...Thomas
MARINE...Thomas