522
FXUS63 KGRR 302317
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
717 PM EDT Mon Jun 30 2025

.KEY MESSAGES...

- Lingering showers and a storm possible into this evening

- Mainly dry with warming temperatures into Saturday

- Next best chance of rain coming late Saturday

&&

.DISCUSSION...
Issued at 308 PM EDT Mon Jun 30 2025

- Lingering showers and a storm possible into this evening

We saw a nice line of showers and storms light up as expected just
before noon today, and most of those have moved east of the area and
weakened already. Those showers and storms look to have formed along
a convergence zone in the shadow of Lake Michigan, where out ahead
of it was instability to the degree of around 2,000 J/kg of CAPE.
Deep layer shear has been very marginal around 20-25 knots, keeping
the storms better behaved.

We are seeing additional spotty shower activity popping up
essentially from U.S.-131 and to the east. There has not really been
any sustained lightning activity with this as instability is not as
robust with CAPEs on the order of 1,000 J/kg. These showers and
isolated thunder are out ahead of the weak cold front (with less
convergence than before) that looks to be located right near U.S.-
131.

These two rounds will be the main chances, but an additional shower
can not be ruled out until the supporting upper wave passes through
the area very late tonight. The diurnal min in instability and Lake
Michigan should limit any additional showers/storms.

- Mainly dry with warming temperatures into Saturday

Even though the front is weak, we will notice a difference in air
masses for a couple of days with temps maxing out in the low to mid
80s and dew points dropping back into the lower 60s. This is a
result of the flow coming in from the NW, and upper heights dropping
a bit.

Rain chances Tuesday and Wednesday afternoon are not zero, but only
as high as about 15% for any one area seeing a brief shower. The
isolated rain chances Tuesday and Wednesday will be mainly along
U.S.-127 where some convergence may help boost cumulus development
enough to spit out a brief/light shower with weak short wave
activity in the NW flow aloft, and mesoscale convergence with the
Great Lakes.

The NW flow will relinquish its hold on the area starting on
Thursday, and then really by Friday/the Fourth. We will see the
boundary between the milder and less humid conditions, and much
warmer and humid conditions arrive later Friday and Saturday. The
arrival of that boundary will raise rain chances a bit. However,
rain chances will max out around 30% at any one location still for
that period, and most areas staying dry.

- Next best chance of rain coming late Saturday

Another upper ridge axis arrives by Saturday, bringing the heat back
to the area with the rising heights. 850 mb temperatures are
forecast to rise to around 20C by Saturday, supporting highs in the
lower 90s and dew points rising into the 60s to lower 70s.

Showers and storms look to increase for the area later Saturday and
into Sunday. The upper ridge axis shifts east, and allows short wave
activity return to the area with a cold front coming in from the NW.
The heat and humidity ahead of it will help to fuel the atmosphere,
and provide for storm chances. These will remain into Sunday, before
some ridging builds in, and cooler temperatures arrive.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 712 PM EDT Mon Jun 30 2025

Skies are clearing currently, but will be short lived as a mid
cloud deck is advecting eastward across the lake in advance of an
upper trough. Region radar also shows some light showers with it,
but suspect that will dissipate as it moves east and stability
increases.

The mid clouds will continue overnight until the trough axis
passes and then we`ll get into drier air with scattered clouds
Tuesday.

&&

.MARINE...
Issued at 308 PM EDT Mon Jun 30 2025

We are looking at a few quiet weather days with regards to boating
and swimming this week. The pressure patterns through Thursday look
relatively weak, keeping winds and waves down a bit.

The winds and resulting waves look to increase enough ahead of the
incoming weekend system that some Small Craft Advisories and Beach
Hazards Statements may be needed for the Holiday. The entire Holiday
weekend will not see the higher winds and waves, but they could be
on and off through Monday.

&&

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

&&

$$

DISCUSSION...NJJ
AVIATION...04
MARINE...NJJ