020
FXUS63 KGRR 170739
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
339 AM EDT Fri Apr 17 2026
.KEY MESSAGES...
- Dense Fog through this morning with fair weather today
- Strong, possible severe storms Friday night
- Cooler, Breezy weekend with cooler and drier weather ahead
&&
.DISCUSSION...
Issued at 253 AM EDT Fri Apr 17 2026
- Dense Fog through this morning with fair weather today
Bottom Line Upfront: Dense fog continues to overspread the region
which has reduced visibilities to 1/4SM or less. This fog will
continue through most of the morning with fog slowly lifting and
visibilities improving late this morning, early this afternoon.
Expect impacts to the morning commute. Have issued a dense fog
advisory accordingly.
The copious amounts of rainfall this week has brought large
amounts of low level moisture across Southern Michigan and
northern Indiana. Soundings show strong inversion at the surface
through the lowest 1KFT with light to calm winds. Dry and slightly
warmer air above will keep the cooler, moisture air trapped this
morning.
The main question is when will the inversion break and the
visibilities improve. With high pressure building overhead, not
expecting for any flow to mix down. Due to that, will need to wait
for daytime heating to allow for warming the surface and dewpoint
depression to drop enough for fog to lift and dissipate. This will
thus take all morning, with conditions improving slowly with fog
lingering through most of the morning and fog finally lifting
between 10 AM and Noon.
- Strong, possible severe storms Friday night
As stated above, High pressure will dominate the weather pattern
today which will bring a welcome reprieve to the wet and stormy
pattern that has dominated Michigan this week. However, those
conditions will be short lived as another frontal system is
expected to move through the region tonight and into Saturday. A
large barotropic low will be moving through central Canada and its
corresponding low and mid levels will swing through an elongated
trough and corresponding front through the Great Lakes Friday
night into early Saturday. Latest CAMS show steep lapse rates
along with good mixed level CAPE. That will correspond with a
strong 45KT LLJ that should provide decent shear along and behind
the front. Mode of convection should be QLCS with potentially
embedded supercells. With soundings being inverted in the lowest
levels there is a potential for strong DCAPE which is an indicator
that damaging winds and large hail are the main threat. There is
also the presence of a cap in the 2 to 5KFT range. This could be a
limiting factor. Another limiting factor will be the time of day,
as this front should be trekking through the area during the
evening.
However, there is a good chance that the LLJ and shear overcomes
those factors and that any cap could also allow the strongest
storms chance to increase enough to break the cap and mix down to
the surface with damaging winds. Due to these concerns
southwestern lower Michigan is either in a marginal to slight
risk.
The storms should move through quickly so not expecting training
storms. However given the inundation of the region, any rainfall
could bring some runoff. QPF remains in the quarter inch to three
quarter inch range. Some overperforming storms could have strong
enough rain rates to put down an inch but will any heavy downpours
will be short lived. Strongest storms should be along and south of
the I 96 corridor but as stated above, additional rainfall is
expected across Lower Michigan. For more discussion of the rivers
please go to the hydro section.
- Cooler, Breezy weekend with cooler and drier weather ahead
The above mentioned cold front will then usher in cooler
northwesterly flow which will allow for cooler temps through the
weekend and into early next week. Strong winds with gusts upwards
of 30 mph are possible late Saturday. Lows Sunday morning will be
at to below freezing with highs on Sunday struggling to get into
the mid 40s. While most would not appreciate the cold, it also
means dry which given the latest moisture will allow for rivers to
recover. A building high over the central US will keep
downsloping flow through the region through at least mid next
week. Temperatures should rebound back into the mid to upper 60s
mid next week.
&&
.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 213 AM EDT Fri Apr 17 2026
The main aviation concern this morning is the fog. A dense fog
advisory will cover all TAF sites. Airport Minimums for visibility
are expect overnight. So far MKG, GRR, JXN have already dropped to
a 1/4SM LAN and AZO have dropped to LIFR. The widespread recent
rainfall, calm winds and inversion will cause these to drop to
VLIFR as well. Cigs are expected to drop to airport minimums as
well. The main question is when these will lift. Latest model
soundings give good credence to fog/mist and LIFR and lower cigs
continuing through most, if not all, the morning. There is a
chance MKG improves between 12Z to 14Z. Cigs and vsbys should
finally improve to VFR between 15Z to 8Z. VFR will continue
through the daytime with clouds infiltrating tonight with showers
and storms possible Friday night into Saturday morning.
&&
.MARINE...
Issued at 313 AM EDT Fri Apr 17 2026
Benign marine conditions are expected through much of the day Friday
before winds and waves increase later Friday into the weekend. A
small craft advisory will take effect tonight and should continue
due to the gusty winds through Saturday into Sunday morning.
Marine Dense Fog will continue into this evening. A line of
thunderstorms should cross the lake tonight with the potential for
winds in excess of 34 knots.
&&
.HYDROLOGY...
Issued at 251 PM EDT Thu Apr 16 2026
Bottom Line Up Front: Significant flooding continues on the Muskegon
River with minor to moderate flooding expected in the Grand River
Basin through the coming days.
Overnight last night, 1 to 3 inches of rain fell across the lower
Muskegon River basin, with isolated pockets in the Grand River basin
as well. This will make its way into the river system resulting in
flooding. Major flooding is expected along the Muskegon River at all
forecast points, with minor to moderate flooding forecast for the
Grand River and its tributaries.
The Kalamazoo River basin seeing less rain of late, no river
flooding is expected. Our Saginaw River basin points at the Chippewa
River at Mt. Pleasant, and the Pine River at Alma are also forecast
to reach minor flood stage.
Little additional rainfall, outside of thunderstorms, is expected
through the daytime hours Friday. Thunderstorms then bring
widespread totals of 0.25-0.75" Friday Night into Saturday, highest
near I-94. Given the saturated antecedent conditions, urban and
small stream flooding is possible with thunderstorms, particularly
Friday Night.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Dense Fog Advisory until 11 AM EDT this morning for MIZ037>040-
043>046-050>052-056>059-064>067-071>074.
MARINE...Dense Fog Advisory until 8 AM EDT this morning for LMZ844>849.
&&
$$
DISCUSSION...Ceru
AVIATION...Ceru
MARINE...Ceru
HYDROLOGY...Thomas
NWS GRR Office Area Forecast Discussion