942
FXUS63 KGRR 210541
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
141 AM EDT Tue Jul 21 2026
.KEY MESSAGES...
- Storms Tonight
- Upper Troughing Continues through next week
&&
.DISCUSSION...
Issued at 258 PM EDT Mon Jul 20 2026
- Storms Tonight
A vigorous upper shortwave trough is phasing with troughing over
eastern Canada, while a deepening surface low north of Lake
Superior drives a cold front into a moist and unstable airmass
across Wisconsin. The convective allowing models show a line of
storms initiating in that area this afternoon then moving
southeast across Lake Michigan and into western Lower Michigan
this evening. They also show a general weakening trend as
instability decreases this evening, although shear profiles remain
impressive.
The main threat appears to be downburst winds associated with
bowing line segments along with isolated large hail in the
strongest, most persistent updrafts. The threat should be ending
Tuesday morning as the cold front pushes through.
- Upper Troughing Continues through next week
The heat and humidity of last week looks to be gone for a while
with all the long range models showing a persistent pattern of
ridging across the SW CONUS and troughing across the NE CONUS.
This will keep the Great Lakes region in a northwest flow regime
for the next week at least, with occasional cold front passages
that could focus convection. The next one appears to be next
weekend. Overall, a cooler and drier than normal weather regime
for the rest of the month is expected.
&&
.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 141 AM EDT Tue Jul 21 2026
Main changes this update were to remove PROB30 thunder mention at
MKG/GRR based on recent radar trends and HRRR guidance. This same
model guidance later develops a band of showers/storms along the
I-94 corridor (AZO-BTL-JXN terminals) in the 10Z timeframe, so
have addressed this with PROB30 groups at those terminals.
Thunderstorms are not that far north of the LAN terminal at this
time and expect at least a chance for thunder based on these
trends. Interestingly, there is another window of possible
thunderstorms at LAN this afternoon, which have been addressed
with another PROB30 group.
Other updates were to be slightly more pessimistic with visibility
restrictions in smoke in the short term before this airmass gets
replaced with post-cold frontal winds. Also think that JXN could
briefly see LLWS thresholds being met given current relatively
weak surface winds.
&&
.MARINE...
Issued at 258 PM EDT Mon Jul 20 2026
SCA continues through Wednesday evening. We may need a Gale
Warning for strong north winds Tuesday night as the pressure
gradient tightens between the departing low and the advancing
high. Conditions will quickly improve on Thursday as the high
builds in.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Wednesday evening for MIZ037-043-
050-056-064-071.
MARINE...Small Craft Advisory until 11 PM EDT Wednesday for LMZ844>849.
&&
$$
DISCUSSION...NJJ
AVIATION...TJT
MARINE...NJJ
NWS GRR Office Area Forecast Discussion
