932
FXUS63 KGRR 040751
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
351 AM EDT Fri Sep 4 2026
.KEY MESSAGES...
- Showers and Storms Once Again Today with Severe Potential
- Period of Dry Weather This Weekend into Early Next Week
- Less Humid Air This Weekend
&&
.DISCUSSION...
Issued at 350 AM EDT Fri Sep 4 2026
- Showers and Storms Once Again Today with Severe Potential
Showers and thunderstorms continue to fill in to our west over
Lake Michigan and Wisconsin. This convection is occurring on the
nose of the low level jet which is aiding in low level theta-e
advection into the storms. The low level jet is forecast, which
was discussed in yesterday afternoon`s AFD, to fold over to the
east and be aimed into Southwest Lower Michigan much of the
morning. Consistency with this feature has been good, which is
something we have not seen of late in the models given somewhat
nebulous forcing which is common in the late summer. Deep layer
shear is expected to be around 40 knots this morning with MUCAPE
values in the 1,000 to 2,000 j/kg range. The parameter space is
robust even at this early hour which is evidenced by nearly 2 inch
hail in the middle of the night to the west of the lake in
Wisconsin.
We expect rounds of storms to move through Southwest Lower
Michigan this morning between 4am and noon. The initial activity
is crossing the lake now and given the surge of low level moisture
via the low level jet severe weather is possible any time during
that window. Its possible some activity may persist slightly past
midday in our south and east towards JXN and LAN, but the
afternoon should trend drier with time. Wind looks to be the main
severe threat with gusts to 60+ mph possible. Severe hail cannot
be ruled out either.
Heavy rain and localized flooding remain possible today given
PWATs near 2.00 inches and the threat of training thunderstorms.
Amounts of 0.50 to 1.00 inches of rain will be likely, but swaths
of 1.50 to 3.00 inches are quite possible as well. Short term
flooding potential will be monitored this morning.
Some redevelopment of showers and storms in the far southwest CWA
towards South Haven will be possible this evening.
- Period of Dry Weather This Weekend into Early Next Week
A period of dry weather is expected this weekend into early next
week as ridging will be in control of the area weather. High
confidence in dry weather this period given consensus in the
ensembles of both the GFS and ECMWF.
- Less Humid Air This Weekend
After what has been a period of very humid air it will be
noticeably less humid this weekend. Dew points are in middle 60s
to around 70 this morning. Dew points in the 50s this weekend will
feel quite pleasant in comparison.
&&
.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 209 AM EDT Fri Sep 4 2026
Another night of patchy fog in place at 06z, some of which is
locally dense with visibilities around 1/2 mile. We may see some
MVFR fog at the TAF sites early this morning but in large part the
lower ceilings and visibilities associated with fog should remain
over Central Lower Michigan.
The bigger threat to aviation interests will be thunderstorms.
Storms have been working this way through Wisconsin overnight and
we expect that trend to continue. Showers and thunderstorms should
move into the area between 07z and 10z and continue into the
daylight hours of Friday morning. By 16z to 18z the storms should
be moving off to the south and east of the area. MVFR conditions
as the storms move through are likely with IFR and lower certainly
possible. Very heavy rain rates are possible which will affect
visibility as well as the potential for stronger winds (in excess
of 40 knots) and hail (to around 1" in diameter).
VFR weather will return this afternoon in the wake of the morning
thunderstorm activity. Bottom line...we are looking at active
weather at the TAF sites especially between 08z and 16z.
&&
.MARINE...
Issued at 350 AM EDT Fri Sep 4 2026
The quiet period (lower waves and winds) continues on the Big Lake
today and into the weekend. Overall, the pattern continues with a
slack gradient today which transitions into surface high pressure
this weekend. Winds should for the most part be in the 5 to 15
knot range. Winds may be slightly stronger on Saturday, but the
flow will be off shore. Waves should be 2 feet or less today
through the weekend.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke
NWS GRR Office Area Forecast Discussion
