552
FXUS63 KGRR 141012
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
612 AM EDT Mon Sep 14 2026

.KEY MESSAGES...

- Showers and Storms Tuesday, Heavy Rain and Isolated Severe Possible

- Low Predictability Heavy Rain Possible Into The Weekend

&&

.DISCUSSION...
Issued at 247 AM EDT Mon Sep 14 2026

- Showers and Storms Tuesday, Heavy Rain and Isolated Severe Possible

Conditons should be dry today with high pressure in place across the
area, before a low deepening in the RRQ of an upper-levle jet will
drive a warm front across the area early Tuesday with a cold front
later Tuesday bringing shower and thunderstorm potential. Low-level
destabilization in conjunction with increased shear from a westerly
jet will support a low chance for gusty winds south of I96.
Depending on where the boundary stalls, PWATs over 2.0" will be
supportive of a heavy rain threat as well, subject to that
placement.

- Low Predictability Heavy Rain Possible Into The Weekend

Predictability falls into mid to late week as the front stalls just
south of the area, with an upper-level pattern dominated by zonal
flow with embedded shortwaves. These patterns are notoriously hard
to pin down. Cluster analysis suggests while there may be dry
periods, there`s not great confidence as to when they will be. A
stalled boundary with persistent high PWATs favors the heavy rain
threat continuing with a WPC Marginal to Slight ERO in place.

Another mid-level wave, low-level jet, and surface low fall into
place going into this weekend. This will bring additional
shower/thunderstorm potential.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 611 AM EDT Mon Sep 14 2026

Satellite trends suggest intermittent fog has developed and may
impact JXN through 12z so have amended to add a TEMPO group to
cover that. Otherwise, expect VFR conditions through the TAF
period with cloud bases lowering to 7-10kft by tonight. Showers
move in after 06z to MKG and may reach GRR by 12z. Otherwise,
winds increase to around 10 knots from the southeast tonight,
higher at MKG with wind gusts to 20-25 knots.

&&

.MARINE...
Issued at 247 AM EDT Mon Sep 14 2026

Conditons deteriorate tonight into Tuesday as an approaching surface
low deepens increasing southerly flow. Enough of a signal for 35-40
knot gales exists north of Holland to hoist a Gale Warning, with a
Small Craft Advisory south of Holland for 22-33 knot gusts. Gales
persist into Tuesday morning with conditions hazardous to small
craft continuing into Tuesday night. Will also hoist a Beach Hazards
Statement from Allegan County north for waves as high as 12 feet.
Will leave Van Buren county out for now with the caveat a 10-20
degree on shore wind shift will bring waves from the 2-4 ft to 3-5
ft range bringing a high swim risk.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from this evening through Tuesday
     evening for MIZ037-043-050-056.
     Beach Hazards Statement from this evening through Tuesday
     afternoon for MIZ064.
MARINE...Small Craft Advisory from 10 PM this evening to 5 PM EDT Tuesday
     for LMZ844-845.
     Gale Warning from 10 PM this evening to 8 AM EDT Tuesday for
     LMZ846>849.

&&

$$

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