213
FXUS63 KGRR 160550
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
150 AM EDT Wed Jul 16 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 /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 150 AM EDT Wed Jul 16 2025

We are looking at a more active forecast period this morning as
compared to the last couple of days. We have a few showers over
the area and even a couple of isolated storms. KMKG and KJXN have
the best immediate threat of the showers and isolated storms
affecting them this morning. Can not rule it out elsewhere, but
will leave it out until they approach the other terminals, if they
do.

We will see these showers/storms dissipate around daybreak, and
have a brief break of no precipitation. Then toward or just after
noon, a few showers and storms will fire close to the lake breeze
boundary. We have a mention at all sites except KMKG who will
likely be west of the activity. These showers/storms will then
dissipate after 22-00z.

Our attention then turns to expected convection over WI and IL
this afternoon and evening. This convection is somewhat uncertain
on how long it will hold on before diminishing later this evening.
For now, the best chance will be at the northern terminals, with a
lower chance at the southern terminals. We have a 2-4 hour period
of this, longest at KMKG where it may persist. Then conditions
should improve just before the end of this forecast period.

&&

.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 until midnight EDT tonight for MIZ050-056-057-
     064-071.
MARINE...None.

&&

$$

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