Turnbull Lake Michigan Weather Forecast Discussion

111
FXUS63 KGRR 141152
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
752 AM EDT Tue Oct 14 2025
.KEY MESSAGES...
- Light rain possible tonight
- More substantial system to affect the area into the weekend
- Temperatures a bit up and down
&&
.DISCUSSION...
Issued at 402 AM EDT Tue Oct 14 2025
- Light rain possible tonight
After a quiet weather day today outside of some areas of morning
fog, rain chances increase tonight. The chances for rain are not
high, generally in the 20-50 pct range. The precipitation tonight
is associated with a push of mid level moisture especially. BUFKIT
overviews show the best juxtaposition of moisture/lift in the
10,000-20,000 foot range. There is not much moisture advection
going on beneath that with lower RH noted around 850mb. The best
places to see lift or implied lift is on the 300k isentropic
surface and in an increase in PWAT values to around 1 inch. Feel
the best chances for rain tonight will be upstream in Wisconsin
and over Lake Michigan, but some of this will slide into Western
Lower Michigan especially. 4hr max reflectivity from the SPC HREF
shows this nicely. The 6hr probability matched mean precipitation
also shows that what precipitation does fall will be light,
generally trace amounts to perhaps a tenth of an inch.
- More substantial system to affect the area into the weekend
Ridging aloft will dominate the remainder of the work week with
dry weather expected from Wednesday midday through Friday. Focus
very much is on the system for Friday night through Sunday as
ridging is replaced by a deep longwave trough which will be
overhead Saturday night into Sunday. Southwest upper flow develops
ahead of the trough Friday night into Saturday. The evolution of
the upper trough has some model differences between the
operational ECMWF and GFS, but we have some things we can nail
down at this point. Those include precipitation will move into the
area Friday night and be most substantial on Saturday it appears
as a cold front drives through the region. Showery weather will
linger into Sunday as we will be beneath core of the upper trough.
Some locally heavy rain is possible during this time frame as PWAT
values climb to 1.5 inches. Thunderstorms are certainly possible
ahead of the cold front as well with 850mb dew points climbing to
+10C and MUCAPE via the ECWMF reaching 1000+ j/kg just upstream.
- Temperatures a bit up and down
Temperatures will be warmer than normal today with highs into the
lower 70s in many areas. Normal highs today are 62 at both GRR
and AZO. We cool a bit for Wednesday and Thursday back into the
60s before rising again ahead of the weekend system. Highs Friday
and Saturday will push back to around 70. Much colder air settles
in with the trough this weekend with highs falling to below normal
values into the 50s. Sunday night 850mb temperatures actually dip
to -1C overhead.
&&
.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 752 AM EDT Tue Oct 14 2025
We are expecting mainly VFR conditions over the course of the next
24 hours...12z Tues to 12z Wed. There is some stratus and fog
around this morning across Southern Lower Michigan, but it is not
widespread in the southwest quarter of the state. At this
time...1148z...all TAF sites are VFR. We may see some brief
periods of fog or stratus this morning, but as of right now VFR is
the expectation.
Stratocumulus is expected to scatter out and clear this morning
with an advancing mid deck taking over this evening and tonight.
These mid clouds will lower and thicken overnight, while
remaining VFR. Showers are expected to move in overnight from the
west, but the precipitation is expected to be light. Visibilities
should not be affected tonight by the very light rain that may
develop.
&&
.MARINE...
Issued at 402 AM EDT Tue Oct 14 2025
The potential for reaching Small Craft Advisory (SCA) conditions
this evening and tonight is not zero, but have decided to hold off
on a headline issuance. High pressure will be pushing into the
region from the north this evening/tonight...and on the leading
edge there is a tightening of the pressure gradient over Lake
Michigan. With time tonight the flow will be veering from north to
northeast increasing the off shore component. We could see some
20 knot winds over the nearshore waters, but this will be of
limited time scale. Waves will increase to around 3 feet tonight,
but we feel they will likely remain below critical thresholds
(4 feet). So, for a marginal event outside of the peak boating
season we will be holding off on a headline for now. We will be
watching trends in modeled winds and waves.
Beyond tonight, high pressure will bring quiescent conditions on
the big lake for Wednesday and Thursday. The next time frame of
concern will be Thursday night into Friday as south flow picks up
to SCA levels. Friday night into Saturday we could even flirt with
gales.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke

NWS GRR Office Area Forecast Discussion