227
FXUS63 KGRR 101908
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
308 PM EDT Wed Jun 10 2026
.KEY MESSAGES...
- Thunderstorm Chances Increase This Evening into Tonight
- Some Significant Severe Weather Possible Thursday Night
- Heat Risk May Continue into Thursday
&&
.DISCUSSION...
Issued at 307 PM EDT Wed Jun 10 2026
- Thunderstorm Chances Increase This Evening into Tonight
SPC continues to include our region in a Slight Risk for severe
weather tonight. Prior to the main window of concern (6pm-12am),
scattered showers and thunderstorms may pop along the lake shadow
boundary this afternoon in the midst of very high SBCAPE values of
3000-4000 J/kg. This mesoscale boundary may act as a localized
source of lift along with the fuel in place to pop some
thunderstorms and provide isolated gusty winds and possibly hail as
well. An isolated severe-level storm is possible but would be the
exception to the rule this afternoon. A second mesoscale feature
we`re watching is the residual outflow boundary from earlier
convection across NE Wisconsin that has now pushed southeast into
central Lake Michigan. This feature could act as another localized
source of lift to interact with thunderstorms slated to move over
the lake this evening.
The setup later this evening will feature a high CAPE but low shear
environment, with our primary focus centering on the potential for
an existing complex of storms moving into northern Illinois to tap
robust instability ahead of it and be propelled over Lake Michigan
later this evening by a strengthening low level jet of 40-50 kts
shown by the RAP13. This complex of storms, while encountering an
environment that has deep layer shear values of only 20 kts across
our region, conversely will be experiencing DCAPE values exceeding
1000 J/kg. This factor, combined with such high PWAT values
(1.75"+), will help compensate the lack of significant shear by at
least locally boosting a damaging wind risk (60 to 70 mph gusts
possible) for areas especially along and west of a RQB-GRR-BTL line
this evening and tonight. Hail may also develop, and a deeper dive
into mid level lapse rates reveals that the setup is better than
initially expected, with HRRR soundings revealing 700-500 mb lapse
rates of 8.0 C/km across SW Lower MI this evening. These same
soundings are not overly concerning for a tornado risk tonight,
however, given the unimpressive 0-3 km wind fields in place.
Subsequent non-severe shower and thunderstorm development late
tonight into early Thursday morning is certainly possible as a LLJ
remains in place through about 06z-09z Thursday. However, the signal
from the 12z HREF 6 hr QPF PMM is not strong, indicating that
repetitive storm development getting draped across the region is
less likely to occur than not. As such, only localized / nuisance
short term flooding is possible tonight mainly across the
traditionally susceptible urban and poor drainage areas. This does
not look to be a major risk at this time but we will monitor.
- Some Significant Severe Weather Possible Thursday Night
A greater risk for severe weather will develop later Thursday,
especially in the 7pm-12am time frame, when both damaging to
destructive wind gusts and tornadoes will be possible. Prior to
this window, generally dry conditions are expected during the day
Thursday. Upper level jet divergence moves in later in the day
along with a robust mid level jet of 50-70 kts moving over Lake
Michigan in the 8pm-11pm time frame. A LLJ around 50 kts is likely
to develop. 12z HRRR soundings at GRR around 00z Thursday evening
show impressive low level shear values with strongly curved
hodographs. For example, the 0-3 km shear is shown to be over 35
kts. The HREF fixed layer significant tornado parameter is showing
values of 3 to 4 along and west of US 131 tomorrow night, which
are quite high. The HRRR is indicating potential for values even
higher than that. While the 12z CAMs generally support an
organized line of storms as the mode, mesocyclonic portions of the
line may develop and the threat for embedded tornadoes is higher
than normal compared to most of our events. Subsequent model
guidance tonight into tomorrow morning will help provide clarity
on the magnitude of this tornado threat, but we are concerned.
The broader risk to the region will be damaging wind gusts and
some swaths of more destructive gusts of 75 mph or greater
possible. SPC has us in the hatched wind gust threat, which is
well warranted given the robust wind field in place via the
soundings. DCAPE values of 1000-1200 J/kg will be present ahead of
the anticipated line of storms moving over the lake late evening.
SBCAPE values of 2000-3000 J/kg should help support storm
intensity beyond the lake crossing, so a rapid weakening is not
expected at this point but a downward trend is likely by the time
storms reach US 127. All told, the potential is certainly there
for Thursday night to be an active night. Between tonight and
Thursday night, power outages are likely to occur in some areas.
- Heat Risk May Continue into Thursday
Given the delay in storm arrival tomorrow, we may be looking at
another day of heat index readings pushing the mid 90s to near 100
especially east of US 131. Will evaluate the need for potential
heat headlines for tomorrow.
&&
.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 142 PM EDT Wed Jun 10 2026
Thunderstorms remain the main concern this afternoon and evening.
Have adjusted the timing as the line of storms will reach the
lakeshore after 22Z. Storms should stream through the region most
likely between 23Z and 02Z. There is a slight chance for some
storms out ahead but that is a low probability so have Prob 30 for
it. After that main line, some overnight showers and storms will
be possible between 03Z and 08Z. Have adjusted timing. IFR to LIFR
cigs and vsbys will be possible in these storms. The main concern
is damaging winds for storms throughout the TAF period is
damaging winds.
The best chance for storms between 03Z and 08Z will be at GRR,
LAN, AZO and BTL. This system should exit the region early
tomorrow morning with it lifting by 10Z at the latest. In its wake
MVFR cigs will be possible through the morning.
Another system will make its way into the region Thursday
evening, bringing another round of showers and storms.
&&
.MARINE...
Issued at 307 PM EDT Wed Jun 10 2026
Waves of 2 to 4 feet are likely into this evening and early
Thursday, likely just staying shy of SCA criteria. However,
Thursday night looks hazardous ahead of a line of storms with SW
winds increasing and a SCA looking likely.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 8 PM EDT this evening for MIZ071>074.
MARINE...None.
&&
$$
DISCUSSION...Hoving
AVIATION...Ceru
MARINE...Hoving
NWS GRR Office Area Forecast Discussion
