774
FXUS63 KGRR 200638
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
238 AM EDT Mon Jul 20 2026
.KEY MESSAGES...
- Thunderstorms Tonight With Damaging Winds Possible
- Dry and Cooler Mid to Late Week
&&
.DISCUSSION...
Issued at 237 AM EDT Mon Jul 20 2026
- Thunderstorms Tonight With Damaging Winds Possible
Primary concern with this forecast package is for the potential of
severe thunderstorms tonight. A cold front looks to trigger storms
across the upper midwest this afternoon which progresses eastward
Monday evening. Questions remain as to the strength of any
convection, with timing favored to be late this evening into the
early overnight hours.
Evaluation of forecast profiles suggests the potential for an MCS on
the nose of a 40 kt LLJ, with strong low-level and deep layer shear.
This lends itself to a primary threat of damaging winds, with large
hail in any discrete convection given steep mid-level lapse rates.
Instability looks to be sufficient as well (albeit waning with
eastward extent), so even with uncertainties as to convective
strength, the environment warrants the Slight (Level 2/5) risk in
place across most of the CWA. The threat ends Tuesday morning as the
cold front exits the CWA.
- Dry and Cooler Mid to Late Week
Tuesday through late week will feature a relatively stable pattern
with persistent upper-level troughing and surface ridging across the
area. Combined with the dry airmass, dry conditons are favored at
this point. Look for highs in the 70s mid-week climbing back into
the low 80s by the weekend.
&&
.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 104 AM EDT Mon Jul 20 2026
Smoke continues to support MVFR conditions at AZO/MKG and IFR at
GRR. Given persistence forecast from previous days, espect
conditions to remain the same through the night if not deteriorate
slightly near daybreak. Mixing then increases favoring VFR
conditions at all terminals beginning mid to late morning. A line
of storms potentially arrives from the west after 00z Tuesday,
however existence of timing and storms remains uncertain. Given
this have elected to go PROB30 at GRR/MKG to start and can re-
evauate with future packages. Gusty winds from the south to around
20 knots are expected today, with locally higher winds and MFVR
and lower conditions possible in any storms tonight.
&&
.MARINE...
Issued at 237 AM EDT Mon Jul 20 2026
Winds and waves increase this morning ahead of a cold front with 3-6
foot waves building by this afternoon. Winds veer northwesterly
Tuesday behind a cold front with waves to 5-8 feet. Winds of 20-30
knots are expected with a 40% chance of gale force gusts Tuesday
evening. Hazardous winds and waves continue into Wednesday evening.
Will hoist a Small Craft Advisory and Beach Hazards Statement for
this multi day hazardous wind and wave event. In addition,
thunderstorms, the strongest of which may have winds in excess of 34
knots, are possible this evening across the nearshore and open
waters.
&&
.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 from 11 AM EDT this morning through
Wednesday evening for MIZ037-043-050-056-064-071.
MARINE...Small Craft Advisory from 11 AM this morning to 11 PM EDT
Wednesday for LMZ844>849.
&&
$$
DISCUSSION...Thomas
AVIATION...Thomas
MARINE...Thomas
NWS GRR Office Area Forecast Discussion
