067
FXUS63 KGRR 290605
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
205 AM EDT Sun Jun 29 2025

.KEY MESSAGES...

- Heat and humidity returns Sunday into Monday

- Thunderstorm chances highest on Monday and next Saturday with a
  few other low chances during the week.

&&

.DISCUSSION...
Issued at 315 PM EDT Sat Jun 28 2025

- Heat and humidity returns Sunday into Monday

After Saturday`s relief with near-normal temperatures and dew points
around 60, Sunday will be another hot day, with uncomfortable
humidity returning and lingering into Monday. The middle 50 percent
of NBM solutions favor highs of 90 on Sunday give or take a couple
degrees. Skies should be mostly to partly sunny with a light
southwest breeze. Dew points Sunday-Monday will also return to
around 70 degrees. This will put heat index values into the mid to
upper 90s on Sunday and near 90 on Monday. Heat exhaustion risk will
be moderate for those outdoors but appears to be just shy of needing
a heat advisory headline.

- Thunderstorm chances highest on Monday and next Saturday with a
  few other low chances during the week.

Sunday to Monday...

A Minnesota-Wisconsin thunderstorm complex is likely to diminish as
it moves into a less unstable environment in the mid levels over
west-central Lwr MI Sunday morning. Went with slight chance of
precip in the US-10 vicinity as a couple of the HREF members hold
onto the elevated convection in that area.

Don`t want to be too confident that nothing will happen Sunday
afternoon given the increasing low-level moisture and potential
leftover 850 mb perturbations. HRRR and ARW are too mixed out and
dry Sun afternoon compared to our dew point forecast. A few CAMs do
pop some isolated showers or storms in mid Michigan within 1000-2000
J/kg CAPE and a weakly sheared environment. Broader scale ridging
will be occurring but will be fairly weak, but the resulting cap
above the PBL may be just enough to prevent convective initiation.

Better synoptic-scale troughing in the Upper Midwest on Monday and a
cold front moving through the area supports likely scattered
thunderstorms during the day. Increasing deep-layer shear may
marginally support locally severe storms with microbursts
possible from pulsing and collapsing hail cores and heavy downpours.

Mid Week into the Holiday Weekend...

The first few days of July are expected to be warm but seasonable
for the time of year in terms of temperature and dew points,
certainly nothing like last week`s heat wave. There are slight
chances around Wed night as spotty showers/storms could develop
along a cold front that trails a northern Ontario low.

Friday to Saturday (July 4-5), warm air and moisture advection over
the region resumes. At least moderate heat impacts may come back
into the picture with the ensembles painting a chance of
temperatures around 90 again. Thunderstorms may also develop with a
front wavering over the region over the holiday weekend, though
increasing spread in the ensemble solutions does not offer firm
details at this time.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 204 AM EDT Sun Jun 29 2025

Limited aviation concerns the next 24 hours with VFR weather
expected for the most part. The exception will be at JXN early
this Sunday morning where some light radiational fog has been
occurring. Conditions through 12Z at JXN may vary between VFR and
MVFR or low visibilities at times. Otherwise, little in the way of
cloud cover is expected. Winds today will become southwest at 5 to
10 knots.

&&

.MARINE...
Issued at 315 PM EDT Sat Jun 28 2025

Winds and waves are forecast to remain below Small Craft
Advisory/Beach Hazards Statement levels through the next several
days. High pressure across the region today is keeping winds light.
Southerly winds increase to 10-15 knots Sunday into Monday ahead of
a cold front. Late Monday into Tuesday, winds veer to northwesterly
behind the front. This cold front will also bring showers and a
chance of thunderstorms Monday into Monday Night.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...CAS
AVIATION...Duke/Thomas
MARINE...Thomas