627
FXUS63 KGRR 170541
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
141 AM EDT Mon Aug 17 2026

.KEY MESSAGES...

- Dense fog along lakeshore, frontal passage this evening

- Showers and storms Tuesday into Wednesday

- Showers and storms potentially next weekend.

&&

.DISCUSSION...
Issued at 253 PM EDT Sun Aug 16 2026

- Dense fog along lakeshore, frontal passage this evening

 Weak zonal flow along with the precipitation from earlier today
has coupled with the temperature differential over the Lake and has
formed dense fog along the lakeshore.

 A cold front is still expected to swing through the area this
evening. This will bring in drier air and shift flow to the
northwest. This will lift/dissipate any fog and will bring an end
to the humid conditions. This cold front is drier than previously
thought, however there remains chances for scattered showers as
it moves through this evening. Several MCV`s moving along the
MI/IN border will remain to the south, especially given the
frontal movement.

- Showers and storms Tuesday into Wednesday

 A weak positively tilted ridge will build over Great Lakes
allowing for drier northwesterly flow to begin the work week.

 This week will be dominated by a large upper level low moving
through Northern Canada. A frontal system stemming from that low
will bring a good chance for showers and storms midweek.
 As the low drops southward over central Ontario, this barotropic
low will extend a deepening mid level trough through the Great
Lakes into Illinois.
  There is a strong upper level jet dynamics that could support
storm growth and will aid in storm dynamics. Couple this with
moist mid levels, thickness advection, a convergent gradient and
a chance for decent CAPE and you have most, if not all, of the
ingredients for decent convection.
 So based on the above and given model consistency, late Tuesday
into Wednesday is the timeframe to watch.

- Showers and storms potentially next weekend.

 The late week pattern is more of an enigma. As the front passes
there is the potential for it to become quasi stationary as the
large upper level low it emanates from moves slowly through north
eastern Canada. That front currently would stretch from the NE
through the Mid Atlantic and across the OH/IN valley to IL.
 So the question is how fast that front propagates eastward.

Temps should remain near, to slightly below, normal through the
week.

Depending when that low ejects into the Atlantic, another
frontal pattern will move in its wake and swing through late in
the week, potentially next weekend bringing chances for more
showers and storms.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 141 AM EDT Mon Aug 17 2026

Few if any changes made for this update. Still expect a brief
period of MVFR fog later this morning, with even IFR fog briefly
possible at GRR. There may also be a MVFR broken cloud layer in
the 4000-5000 ft AGL range developing later this morning which
could serve to reduce visibility restrictions in fog somewhat.
MVFR ceilings are expected to dissipate, yielding VFR conditions
areawide by this afternoon. Although not explicitly stated in the
TAFs, VFR conditions are expected to continue through 06Z Monday
night.


&&

.MARINE...
Issued at 253 PM EDT Sun Aug 16 2026

Trapped moisture aided by recent rainfall and humidity has cause
dense fog along the lakeshore this morning. Winds remain fairly
light so expecting this fog to continue through at least the first
half of the afternoon until the winds shift when the cold front
comes through early this evening.

West winds become north tonight behind the front. A few
showers and potentially a storm are possible over Lake Michigan
this evening along the front.

Waves will be 1 to 2 feet with a low swim risk through. The north
winds should kick up 2 to 3 foot waves tonight. A low swim risk
is expected Monday, then a moderate swim risk Tuesday with
southwest winds with winds and waves that could be near SCA
criteria Tuesday into Wednesday.

&&

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

&&

$$

DISCUSSION...Ceru
AVIATION...TJT
MARINE...Ceru