Leroy, Michigan Weather Forecast Discussion

491
FXUS63 KGRR 070357
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
1157 PM EDT Sat Sep 6 2025
.KEY MESSAGES...
- Increasing rain chances tonight, especially near the lakeshore
- Lake effect showers tapering off Sunday
- Increasingly warmer next week with limited precipitation chances
&&
.DISCUSSION...
Issued at 249 PM EDT Sat Sep 6 2025
- Increasing rain chances tonight, especially near the lakeshore
Some showers have developed thanks to a combination of diurnal
destabilization and an upper PV max (best seen on the GOES channel
08 IR/WV imagery) crossing southern Lower MI. There is an associated
surface boundary traversing the area as noted by veering winds to
the northwest at the lakeshore on the western side of this boundary.
There probably will be a brief lull in precipitation this
afternoon/evening. Precipitation chances increase substantially
after 8 PM and particularly after 11 PM as a stronger upper PV max
currently over northern MN swings across MI. The best juxtaposition
of PV forcing and large lapse rates (which augments response to this
forcing) will be over central and northern Lower MI. This is where
the SPC Day1 outlook advertises General thunder. There is a low
chance for thunder farther south, but not terrific. Bufkit profiles
over southern Lake MI show CAPE at its peak depth barely poking into
the DGZ, so we are probably looking at just lake effect rain showers
with continued shallow cloud depths (less than 10k feet) mitigating
intensity of rainfall. Greatest rain chances will be at the lakeshore,
but measurable precipitation could extend inland substantially
based on a forecast plume of conditional instability (moderately
negative 0-2km theta-e lapse rates) extending from Lake MI across
much of SW Lower MI.
- Lake effect showers tapering off Sunday
Lingering lake effect rain may affect far SW Lower MI early in the
day along with exiting showers over Central Lower MI. However,
Sunday will be predominantly dry as surface high pressure becomes
centered over the western Great Lakes in response to downward PV
forcing with increasingly NW flow aloft.
- Increasingly warmer next week with limited precipitation
chances
As noted previously, we are looking at a frontal system that will
have a hard time making it east into the area given weak and poorly
phased troughing aloft.  Although high pressure does move east of
the area and allow southerly flow to resume, trajectories off the
Gulf are sub-optimal for moisture return in our area. Wednesday could
be our warmest day with highs reaching the 80s south of I-96.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 723 PM EDT Sat Sep 6 2025
VFR conditions will continue through Sunday afternoon, with west
winds about 5 to 10 knots.
&&
.MARINE...
Issued at 1155 PM EDT Sat Sep 6 2025
The SCA and BHS have been dropped as conditions have improved
below criteria and there is doubt as to whether conditions will
reach criteria again in the next 12 hours.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...TJT
AVIATION...Ostuno
MARINE...Ostuno/Thomas

NWS GRR Office Area Forecast Discussion