471
FXUS63 KGRR 180635
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
235 AM EDT Sat Jul 18 2026
.KEY MESSAGES...
- Scattered Showers and Storms Saturday Morning/Early Afternoon
- Showers and Storms With Severe Weather Possible Monday Night
- Dry and Cooler Mid to Late Week
&&
.DISCUSSION...
Issued at 234 AM EDT Sat Jul 18 2026
- Scattered Showers and Storms Saturday Morning/Early Afternoon
A cold front sits across Central Wisconsin based on surface
observations and will reach the area early this morning and sweep
southeast through early afternoon. Short range model guidance shows
a broken line of storms is likely to develop. Forecast soundings
suggest MLCAPE over 2000 J/kg with MUCAPE over 3000 J/kg. Deep layer
shear is marginal around 25-30 knots, but mid-level winds around 35
knots and DCAPE around 1000 J/kg suggests a damaging wind threat in
any storms that organize. The greatest potential is across our
southeast forecast area where surface based instability builds ahead
of the front. Around 100 effective SRH suggests a low but not zero
risk of a tornado if an embedded supercell can develop. Smoke then
filters back in this afternoon/evening behind the front.
- Showers and Storms With Severe Weather Possible Monday Night
High pressure moves into the region behind the front keeping things
dry for Sunday ahead of the next system. Attention then turns to
Monday Night as a shortwave drives a cold front across the area.
MUCAPE north of 1000 J/kg and ample low and mid-level jets suggest
that storms along this front could be severe, with damaging winds as
the favored hazard given anticipated mode. The caveat to this is
that nocturnal timing is less favorable with increasing low-level
stability with time. However, given the thermodynamic and kinematic
parameter space, trends will need to be monitored.
- Dry and Cooler Mid to Late Week
Northwest flow and surface ridging then set in behind the cold front
bringing dry and cooler conditions to the area. As 850mb temps fall
into the lower 10s to upper single digits C, highs will fall to near
80F mid to late next week.
&&
.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 104 AM EDT Sat Jul 18 2026
Lingering smoke should clear shortly leading to VFR conditions
areawide. A front crossing the area after 12z will lead to a
broken line of showers and storms. Given low probabilities of
direct terminal impacts have elected to start with a PROB30 too
highlight the best impact window. MVFR and lower conditions and
wind gusts over 30 knots are possible in any storms. Smoke then
returns late Saturday afternoon into the evening. Used RRFS smoke
for timing, with confidence in any restrictions low at this time.
Outside of storms expect southwest gusts to around 20 knots
becoming northwest behind the front.
&&
.MARINE...
Issued at 234 AM EDT Sat Jul 18 2026
A Beach Hazards Statement and Small Craft Advisory are currently in
effect for a two part hazardous wind and wave event this morning
through Sunday morning. Southwest winds and waves increase to 15-20
knots late tonight into Saturday morning with 3-5 foot waves. Behind
the front this afternoon/evening sees winds increase from the
northwest to around 20 knots with 3-6 foot waves keeping waves
hazardous. Winds then go offshore tonight causing waves to subside.
A break in winds and waves then is expected until later Monday into
Tuesday when winds and waves increase again potentially becoming
hazardous. In addition, isolated thunderstorms are possible again
today with storms possible again Monday night.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert until midnight EDT tonight for MIZ037>040-
043>046-050>052-056>059-064>067-071>074.
Beach Hazards Statement through late tonight for MIZ037-043-050-
056-064-071.
MARINE...Small Craft Advisory until 4 AM EDT Sunday for LMZ844>849.
&&
$$
DISCUSSION...Thomas
AVIATION...Thomas
MARINE...Thomas
NWS GRR Office Area Forecast Discussion
