441
FXUS63 KGRR 111846
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
246 PM EDT Mon Aug 11 2025

.KEY MESSAGES...

- Scattered Showers and Storms Today and Tonight

- Showers and Storms Likely Tuesday With A Few Severe Storms Possible

- Cooler and Dry Late Week

- Hot This Weekend With Showers/Storms Possible

&&

.DISCUSSION...
Issued at 245 PM EDT Mon Aug 11 2025

- Scattered Showers and Storms Today and Tonight

Scattered showers and storms are already developing across parts of
West Michigan this afternoon due to a low-level convergence axis.
The greatest chance for any precipitation is east of a Clare to
Ionia to South Haven line. With effective shear less than 20 knots,
storms will be disorganized with locally heavy rainfall and
lightning as the main threats. If a few stronger cores can develop,
isolated gusts in excess of 40 mph are possible. A second round of
showers and storms is expected across much of the area overnight
into Tuesday morning as an MCV currently across northeast Kansas
acts in concert with the low-level jet. Once again, a few storms
with gusty winds cannot be ruled out though confidence is low.

- Showers and Storms Likely Tuesday With A Few Severe Storms Possible

Attention then turns to Tuesday afternoon, when a dying cold front
that stalls across northwest Michigan Monday Night likely serves as
the focus for convective development in the afternoon and evening.
Even with a warm profile supportive of marginal mid-level lapse
rates, a very moist profile in conjunction with diurnal heating
will lead to ample CAPE to support thunderstorms. The arrival of a
35-40 knot 700 mb jet in the afternoon will increase deep layer
shear to the 25-35 knot range allowing some potential for
convective organization. The HREF captures this well with UH
swaths across the southern half of the CWA in the afternoon and
evening.

This will bring the potential for strong to severe storms Tuesday
afternoon and evening. The primary concern is for damaging wind
gusts to around 60 mph in any transient supercell structures or
bowing segments that develop. Locally heavy rainfall will also be a
concern given the very moist airmass with the HREF 24 hr LPMM
suggesting that any areas with training storms may see rainfall over
3 inches. The best chance for this is across southern Michigan.

- Cooler and Dry Late Week

Mid-level troughing persists over the area for Wednesday keeping
850mb temps in the mid teens Celsius. This will keep conditions
relatively cool Wednesday into Thursday with highs in the low 80s.

As for precipitation, cannot rule out isolated showers to start the
day Wednesday across our southeast forecast area as the cold front
exits. Then surface ridging takes over with dry conditions expected
through the rest of the work week. Dewpoints in the upper 50s to low
60s will also feel more comfortable than recent days.

- Hot This Weekend With Showers/Storms Possible

Upper level ridging returns this weekend with 850mb temps climbing
into the low 20s Celsius translating into high temps in the upper
80s to low 90s once again. Showers and storms are possible as an MCS
complex triggered off of a frontal boundary may develop. Where any
such complex would propagate is uncertain at this range with
possible scenarios including storms staying north of West Michigan
or making it into part or most of the area.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 135 PM EDT Mon Aug 11 2025

VFR cu will continue through the rest of the afternoon. We`re also
watching radar trends for the potential of developing
showers/isolated thunderstorms this afternoon and evening. An
approaching upper trough tonight will keep the chance of at least
showers in the TAFs. Confidence is low in exact timing and
location for thunderstorm development and so was left out of the
TAFs.

&&

.MARINE...
Issued at 135 PM EDT Mon Aug 11 2025

Wind and waves will diminish late this afternoon and evening and
remain relatively light for the next few days. Marine and beach
hazards will exist for the remainder of this afternoon.

Scattered thunderstorms will remain a hazard to boaters and beach
goers through Tuesday night.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 5 PM EDT this afternoon for MIZ050-
     056-064-071.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for
     LMZ844>847.

&&

$$

DISCUSSION...Thomas
AVIATION...04
MARINE...04