737
FXUS63 KGRR 091142
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
642 AM EST Sun Nov 9 2025

.KEY MESSAGES...

- Synoptic snow mainly south of I-96 this morning

- Lake effect snow northwest this morning and today

- Lake effect snow tonight east of US-127

- Cold Monday morning, additional lake effect into Monday night

&&

.DISCUSSION...
Issued at 311 AM EST Sun Nov 9 2025

- Synoptic snow mainly south of I-96 this morning

The changeover to snow was quicker than anticipated. However, radar
currently indicates decreasing reflectivities, suggesting that lower
tropospheric frontogenetic forcing originally just south of I-96
is weakening as it drifts north. MIDOT webcams indicate that roads
are wet and RWIS data show road surface temperatures in the lower
to mid 30s areawide. Hence, travel impacts are not anticipated.

- Lake effect snow northwest this morning and today

As noted previously, the main area of concern is Mason/Oceana
counties, where a winter weather advisory is in effect. GRB radar
currently shows a developing mesolow over Lake Michigan northwest
of Ludington. This mesolow even has a well defined eye to it,
indicating significant latent heat release with convective lake
effect snow (LES) band. This supports the notion of very
significant lake induced conditional instability supportive of
intense convective snowfall...and even perhaps thundersnow later
today into tonight. The 09/06Z HRRR picks up on this mesolow and
uses it to drop a burst of snow that clips western Mason/Oceana
counties. Radar currently suggests the mesolow and burst of snow
may stay a bit further offshore than the models advertise, but
that could change. With the passage of the mesolow, the dominant
LES band will likely stay even farther offshore for quite a while.
However, guidance shows this band making another push inland late
Monday morning with additional significant snowfall. This is
beyond the valid time of the advisory and thus the advisory may
have to be adjusted accordingly.

- Lake effect snow tonight east of US-127

We continue to see a signal for LES off Saginaw Bay early tonight
that could drop a relatively quick 4 inches or so north of St Johns
in the Alma vicinity. Air temperatures will be dropping into the low
20s around the time this occurs, so accumulating snow on roadways
seems plausible. As noted previously, this is a borderline
advisory scenario affecting a relatively small part of our CWA.
Will let the day shift assess with the latest suite of available
CAM guidance.

- Cold Monday morning, additional lake effect into Monday night

Monday morning temperatures will range from the upper teens to
lower 20s, which would make roadways better able to accommodate
accumulating snow. The best chances for accumulating snow around
this time would be in Mason/Oceana counties, with lighter
accumulation also possible southeast of a South Haven to Mount
Pleasant line.

Newest guidance, including the 09/06Z HRRR, indicates a second
round of LES Monday into Monday night setting up over southwest
Lower MI in response to an upper PV lobe trailing the main upper
low. An advisory will probably need to be considered for the Van
Buren and Allegan County area if current trends hold.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 642 AM EST Sun Nov 9 2025

Key changes:
- introduced early period of IFR/fuel alternate MVFR ceilings
- added early IFR vis restrictions in -SN for southern terminals

Radar indicates frontogenetically forced snow extending from the
AZO to LAN terminal as of 1130 UTC with an additional band of snow
in the vicinity of GRR. This activity is expected to shift east
causing brief IFR ceiling/visibility restrictions in snow at the
LAN-JXN-BTL terminals early this morning. A general lull in
precipitation is expected late morning into afternoon; however,
there is uncertainty regarding how quickly ceilings will rise. We
are advertising a gradual transition to MVFR fuel alternate
(1000-1900 ft AGL) by late morning and possibly exceeding 3000
feet by afternoon. However, this may be optimistic at some of the
inland terminals. MKG might maintain and keep VFR conditions as
flow is veered to a more offshore direction in response to a
powerful lake effect snow band extending down the long axis of
Lake Michigan.

Another round of lake effect snow is expected tonight with many
terminals experiencing sporadic IFR ceiling and visibility
restrictions.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 7 PM EST this evening for MIZ037-
     043.
MARINE...Small Craft Advisory until 7 PM EST Monday for LMZ844>849.

&&

$$

DISCUSSION...TJT
AVIATION...TJT