168
FXUS63 KGRR 131859
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
259 PM EDT Thu Aug 13 2026

.KEY MESSAGES...

- Showers possible through south, Patchy Dense Fog Friday morning

- Showers/storms Friday night into Sunday; Heavy Rain possible Saturday

- Dry to begin next week, chances for precipitation midweek


&&

.DISCUSSION...
Issued at 250 PM EDT Thu Aug 13 2026

- Showers Possible through South, Patchy Dense Fog Friday morning

Another MCS is moving from the west. This system is moving slower
than yesterday`s, but like the last few days the pattern and axis
of convection will keep showers and storms primarily south of
Michigan. There is a slight chance that the fringes of the MCS
clips south of the I 94 corridor.
 With the overall pattern remaining in place, the light winds and
moisture at the surface will once allow for fog Friday morning.
 Winds will be out of the north to northeast so slightly less
moisture so while there will be fog, it should not be as dense as
Thursday morning.

- Showers/storms Friday night into Sunday; Heavy Rain possible Saturday

 The pattern begins to change Friday. Another ribbon of moisture
and front will swing down Friday. Any convection from that should
will be similar as the last few days, only clipping far southern
Michigan.
 However, the flow will shift to the north Friday night into
Saturday. This will bring warm air advection, and a strong 850mb
jet through the region Saturday.
 That jet, along with potential mid level shortwaves, will bring a
chance for strong to severe storms Saturday. Anomalous moisture
associated with this system will also mean heavy rainfall will be
possible Saturday through Saturday night.
 As such, SPC has MI in a marginal risk, south of the I 96
corridor. There is also a slight risk of excessive rainfall
through that region as well.
 Another wave associated with a 500 mb trough and a deepening
upper level low will move through the UPPER Great Lakes Sunday.
This will bring further chances for showers and storms Sunday.


- Dry to begin next week, chances for precipitation midweek

 Temperatures are trending near normal, to slightly below normal.
A mid level ridge in the wave of the trough will allow for dry
weather through the first half of next week.
 Another upper level low moving through central Canada is tracking
a long wave trough through the area Wednesday. Mid to long range
models are fairly consistent at this time so that could allow
for showers and storms mid next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 127 PM EDT Thu Aug 13 2026

Latest IR loop shows a high overcast from an MCS moving across
Illinois. The rain will likely dissipate before it reaches the
southern terminals late this afternoon. Otherwise, the northern
terminals will remain VFR through the period. The southern
terminals will see some MVFR fog overnight due to recent rainfall
adding to the low level moisture aggregate.

&&

.MARINE...
Issued at 250 PM EDT Thu Aug 13 2026

The main marine issue through Friday will be the potential for fog
headlines given the moisture and light winds. While can`t rule out
the potential for showers and storms through the far southern
zones, it should remain closer to IN. The weekend will bring the
potential for headlines with winds and waves strengthening into
the weekend. Winds though will be off shore into Saturday morning.


&&

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

&&

$$

DISCUSSION...Ceru
AVIATION...04
MARINE...Ceru