468
FXUS63 KGRR 152258
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
658 PM EDT Tue Jul 15 2025

.KEY MESSAGES...

- Strong to Severe Storms Possible Wednesday Afternoon and Evening

- Dry And Cooler Later Thursday And Friday

- Showers and Storms Possible Saturday

&&

.DISCUSSION...
Issued at 259 PM EDT Tue Jul 15 2025

- Strong to Severe Storms Possible Wednesday Afternoon and Evening

Dry conditions are expected the rest of today before showers and
thunderstorms return to the forecast for Wednesday. Two rounds of
thunderstorms are forecast, with both capable of damaging winds in
the strongest storms.

The first round of storms is expected to develop Wednesday afternoon
off of the lake breeze, with scattered storms near and east of
US131. The airmass will be quite humid with PWATs north of 1.5".
Heavy rain and lightning are the greatest concerns with these
storms. Although shear is poor, with mean SBCAPE values near or
above 2000 J/kg, isolated wet microbursts cannot be ruled out.

Attention then turns to the storms that will develop Wednesday
afternoon across Wisconsin and Illinois. These storms will fire off
of a cold front Wednesday and be aided by an MCV as they move
eastward. These storms will become more linear with time, reaching
the lakeshore in the mid to late evening. Compared to the daytime
environment, increasing mid-level winds will support better shear,
on the order of 25-35 knots. This is a conditional threat, as it is
uncertain whether storms will survive the journey over the lake
given the displacement of the mid-level jet to the north and lack of
a low-level jet or robust EML. The best chance for any storms to
survive appears to be near and north of I96 at this time being
closer to the jet/MCV and having slightly better delta Ts. If storms
can survive across the lake, damaging winds are possible with this
line. We will monitor this closely over the next 24 hours.

The cold front then arrives Thursday morning keeping the potential
for at least scattered showers and storms in the forecast to start
the day. Given the unfavorable morning timing of fropa, severe
storms are not expected with the front itself.

- Dry And Cooler Later Thursday And Friday

Dry air filters into the area later Thursday into Friday with the
arrival of surface ridging. Look for highs in the upper 70s to low
80s with decreasing cloud cover, especially for Friday.

- Showers and Storms Possible Saturday

Precipitation returns to the forecast Saturday with the interaction
of a mid-level wave and a frontal boundary across the Ohio Valley.
Exact timing and placement of the vorticity maxima remain uncertain
at this range, though the overall pattern suggests that the best
chance will be late Saturday into Saturday Night across the southern
half to two-thirds of the forecast area.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 658 PM EDT Tue Jul 15 2025

VFR is expected to be the predominant condition through much of
the night. However, higher moisture around 5,000 feet is moving
toward Southwest Michigan from Indiana, and this may create
scattered clouds and a chance of a moderate rain shower late
tonight or early Wed morning. Fair confidence in scattered showers
and thunderstorms developing after 16 Z, mainly east of a
AZO-GRR-RQB-CAD line. For now left it as prob30 over a broad
window of time until it can be narrowed down.

&&

.MARINE...
Issued at 152 PM EDT Tue Jul 15 2025

Low swim risk and 1 to 2 ft waves through Wednesday with a wind
component mostly from the south. Thunderstorms will attempt to
cross Lake Michigan late Wednesday evening and some may be
successful. If so, lightning and wind gusts greater than 30 or 35
knots would be possible. Small craft advisory and beach hazards
statement (high swim risk) is likely for Thursday as winds
strengthen from the north.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert from midnight tonight to midnight EDT
     Wednesday night for MIZ050-056-057-064-071.
MARINE...None.

&&

$$

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