421
FXUS63 KGRR 251814
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
214 PM EDT Tue Aug 25 2026
.KEY MESSAGES...
- Patchy Fog into Mid Morning
- Chance for Thunderstorms Wednesday, Some Strong
- Warmer & More Humid Sunday into Early Next Week; Storms Possible
&&
.DISCUSSION...
Issued at 248 AM EDT Tue Aug 25 2026
- Patchy Fog into Mid Morning
NBM hourly guidance as well as GFS MOS guidance continues to
support a few hours of patchy fog mainly from 5am-9am this
morning. Some could be locally dense. Low or zero dew point
depressions, calm winds, and clear low/mid levels (just some
scattered high clouds) should allow for some patchy fog. Will
assess observation trends into mid morning, but confidence is not
high that any headlines will be needed.
- Chance for Thunderstorms Wednesday, Some Strong
Model guidance continues to support scattered thunderstorms across
the region Wednesday. Since we are now within 36 hours of the
event, the CAMs are helping fine tune what the threat could be.
00z HREF guidance indicates a surface cold front will be located
across western Lake Michigan by 18z Wednesday. Ahead of the front,
the HREF mean is showing a plume of 1500 J/kg SBCAPE with maximum
members indicating over 2000 J/kg. HRRR soundings for 18z at LAN
show a bit more decent shear than previously indicated with 0-6km
shear around 30 kts with decent directional shear in the 0-3km
layer. Some of the Nam3km soundings look more ominous for low
level shear ahead of the front. Overall, there appears to be
enough shear and instability along with some low level curvature
in the model hodographs to support some severe potential,
including perhaps some clusters of storms with embedded strong
winds or even some mini-supercells capable of a short duration
tornado.
Some questions exist about midday shower activity prior to peak
daytime heating. Some CAMs do indicate scattered morning showers
moving into western Lower MI, which could complicate pre-frontal
storm development in this area. Indeed, models such as the HRRR
push showers through GRR around the lunch hour and effectively end
the storm threat for the day there. We`ll see how this pans out.
The Nam3km would delay storms a bit, which could bring more of a
severe weather threat to the area. If we had to highlight a
particular region for strong storm development, it seems east of
US 131 may have the best threat from 18z-00z Wednesday.
As previously mentioned, a few diurnally driven showers and a
thunderstorms may develop on Thursday mainly near and east of US
127 given residual instability and moisture left in the area
underneath upper troughing. Currently NBM isn`t buying it, with
POPs too low to mention a threat for rain.
- Warmer & More Humid Sunday into Early Next Week; Storms Possible
After we`ve gone through some fallish weather lately, it appears
we`ll reverse course a bit late weekend into early next week as
anomalous upper heights move in per ensemble guidance (500 mb
heights in the upper 580s dm) as well as 850mb temps that could
even touch 20C across southern Lower MI. This also occurs with
climbing dew points and PWAT values, as well as an active low
level jet pattern somewhere across the Midwest. Depending on where
we sit with relation to the upper ridge and low level jet, periods
of thunderstorms are certainly possible.
&&
.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 210 PM EDT Tue Aug 25 2026
VFR conditions and light/variable winds will prevail at all West
Michigan TAF sites this afternoon into this evening, with surface
high pressure overhead. As the high slips to the east, light SSW
winds and weak warm air advection will commence. This will result
in thickening mid-upper cloudiness after midnight.
Thanks to said warm air advection, increasing low level moisture,
and approaching cold front, a risk for showers/storms will be
introduced after 12Z Wednesday at MKG/GRR/AZO/BTL. Will
tentatively refrain from adding precipitation at LAN/JXN through
18Z.
&&
.MARINE...
Issued at 248 AM EDT Tue Aug 25 2026
Wednesday will be the next hazardous day for mariners and also
lead to a high swim risk for many areas, especially Holland to the
north. This occurs ahead of a cold front likely situated across
western Lake Michigan around 18z Wednesday. Mariners will face
increasing wind and wave activity, likely necessitating a Small
Craft Advisory for Wednesday with 3 to 6 footers possible and SW
winds 10-20 kts and gusts to 25 kts.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from late tonight through Wednesday
evening for MIZ037-043-050-056-064-071.
MARINE...Small Craft Advisory from 2 AM Wednesday to midnight EDT
Wednesday night for LMZ844>849.
&&
$$
DISCUSSION...Hoving
AVIATION...Smith
MARINE...Hoving
NWS GRR Office Area Forecast Discussion
