012
FXUS63 KGRR 301856
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
256 PM EDT Sun Aug 30 2026
.KEY MESSAGES...
- Warm, Humid, Occasional Thunderstorms Through Midweek
&&
.DISCUSSION...
Issued at 256 PM EDT Sun Aug 30 2026
A strengthening heat dome over the southern to southeast CONUS
the next few days will send hot and humid air into portions of
Lower Michigan. The unsettled "ring of fire" pattern returns at
least through Wednesday as a surface front wavers north then back
south underneath upper-level shortwaves and jet streaks. Global
ensemble systems offer good confidence in heat and humidity
building through Wednesday, then fair confidence for some relief
from the hotter temperatures for the latter part of the week.
Though dependent on thunderstorms each day, high temperatures
around 90 and a heat index climbing to 95-100 are possible in
southwest and south-central Lower Michigan Tuesday and Wednesday.
This evening, a midlevel vorticity center moving through southern
WI and northern IL is touching off showers and thunderstorms.
This morning`s models have not been enthusiastic about the
thunderstorm potential in southwest Michigan this evening, given a
capped surface and poor midlevel lapse rates and limited CAPE
environment that this disturbance will move into. But will
maintain showers and a slight chance of a thunderstorm for this
evening mainly south of I-96.
Early Monday, the nose of a 850-700 mb jet will be pointed at
western and central Lwr MI, where somewhat better but still modest
CAPE around 500 J/kg will exist. This provides another chance of
scattered thunderstorms, which will again be relatively high-based
as most of the moisture will be above 800 mb and closer to 700 mb
or 10,000 feet.
Confidence in the timing of subsequent rounds of thunderstorms
from Monday night to Wednesday is quite low, but models increase
CAPE values, and adequate deep-layer shear will be in place much
of the time. This will set up at least marginal threats for severe
weather during this period.
&&
.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 137 PM EDT Sun Aug 30 2026
A minor short wave moving east across Wisconsin will result in a
few showers and possibly a thunderstorm near the southern
terminals later this afternoon and evening.
A W-E oriented LLJ will result in some LLWS at MKG/GRR overnight.
MVFR fog is also possible after midnight due to high dewpoints and
residual moisture from recent rain.
&&
.MARINE...
Issued at 256 PM EDT Sun Aug 30 2026
Small Craft Advisory / Beach Hazard Statement is working out well
this afternoon, with a marginal wind and wave threat for small
craft south of South Haven and moderate swim risk, and more
hazardous winds and waves to the north of South Haven toward
Ludington. The Port Sheldon buoy has been gusting to 30 knots from
the south and waves have been 4 to 6 feet. The South Haven buoy
has had waves more in the range of 2 to 4 feet. Hazardous
conditions will only gradually subside this evening, and the
advisory is on track to end at 11 PM. However, this break in the
hazard will be short.
South-southwest winds are expected to strengthen to 15 to 25
knots again Monday. The models do not have a uniform and smooth
wind field over the lake as it may be disrupted in spots by
showers and thunderstorms Monday morning, though generally these
winds will again build up 3 to 6 foot waves, hazardous for small
craft and swimmers. Anticipating a moderate swim risk with 2-4 ft
waves from St Joseph to Holland, and a high swim risk with 3-6 ft
waves north of Holland toward Ludington.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 11 PM EDT this evening for MIZ037-
043-050-056-064.
MARINE...Small Craft Advisory until 11 PM EDT this evening for LMZ844>849.
&&
$$
DISCUSSION...CAS
AVIATION...04
MARINE...CAS
NWS GRR Office Area Forecast Discussion
