050
FXUS63 KGRR 240739
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
339 AM EDT Tue Jun 24 2025

.KEY MESSAGES...

- Heat Slightly Improves this Week

- Periods of Rain and Thunderstorms this Week

&&

.DISCUSSION...
Issued at 339 AM EDT Tue Jun 24 2025

- Heat Slightly Improves this Week

A Heat Advisory remains in effect along and south of a Holland to
Lansing line with heat indices around 100 expected. Areas north
of this line heat indices will be in the 90s with isolated spots
approaching 100. Make sure to limit time outdoors, stay hydrated,
and check on those without AC.

The heat scales back slightly this week with highs in the 70s and
80s, however dew points will largely remain in the 60s to low 70s
so it will still feel rather muggy outside. We`ll have to watch
for heat indices to approach 100 again over the weekend.

- Periods of Rain and Thunderstorms this Week

Our overall environment through the weekend will have instability
and moisture available each day under the upper level ridge. Any
source of lift has the potential to spark off showers and
thunderstorms, therefore the probability of precipitation will be
in the 20 to 50 percent range through most of the forecast.

Not any one day looks to be a complete washout as sources of lift
look to be progressive. The timing and source of lift varies from
model to model, therefore there is some uncertainty. Timing will
likely be better known the day of in this type of environment.

Today our main focus for shower and thunderstorm development will
be this afternoon mainly along and south of a frontal boundary
around Kalamazoo to Lansing. There will also be some positive
vorticity advection in play from the dying convection over
Wisconsin. As daytime heating occurs and we are able to tap into
the surface based instability around 2000 J/kg we should see
thunderstorms develop with these sources of lift. Again the best
chances 40 percent or greater are along and south of a Kalamazoo
to Lansing line. With precipitable water values approaching 2
inches would expect heavy downpours with any thunderstorm.
Additionally with modest shear and some dry air toward the surface
there could be a few stronger storms that could produce some
stronger winds.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 149 AM EDT Tue Jun 24 2025

VFR conditions continue through Tuesday morning. With daytime
heating Tuesday afternoon showers and thunderstorms will be
possible (20 to 50 percent). The best chances will be along and
south of a AZO to LAN line where the best instability is along
with a weak boundary. There is a potential for stronger storms
producing stronger gusts to 40 knots.

Overall southwesterly winds gradually become more westerly with
gusts around 20 knots this afternoon. Winds become light and
variable after OOZ Wednesday.

&&

.MARINE...
Issued at 339 AM EDT Tue Jun 24 2025

Thunderstorms will be the main concern into the weekend as winds
and waves are forecast to remain below Small Craft Advisory and
Beach Hazard Statement levels. The best chance for thunderstorms
will be this afternoon and evening (20 to 30 percent). A few
storms could produce stronger winds causing a brief increase in
wave heights.

Through the remainder of the week off and on chances for rain and
thunderstorms are expected with the best chances each afternoon.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 8 PM EDT this evening for MIZ064>067-071>074.
MARINE...None.

&&

$$

DISCUSSION...RAH
AVIATION...RAH
MARINE...RAH