616
FXUS63 KGRR 111051
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
651 AM EDT Thu Jun 11 2026

.KEY MESSAGES...

- Severe weather likely this evening

- Turning cooler behind a Sunday cold front

&&

.DISCUSSION...
Issued at 414 AM EDT Thu Jun 11 2026

- Severe weather likely this evening

A complex scenario today in regard to severe weather as the
morphology of the event is not certain off to our west during the
day. That said, what pushes into Southwest Lower Michigan this
evening could be significant including threats of all hazards,
damaging winds, large hail, tornadoes and torrential rain.

A sharp shortwave trough is plowing east from the Northern Rockies
into the Plains states tonight with convection already developing
in Nebraska (more on this in a bit). Strong mid and upper level
winds are inferred from both satellite and radar imagery as
clouds/echoes are shearing downstream rapidly. The upper wave
moves eastward today across the Plains which will pull a surface
low northward into Wisconsin by evening. The Nebraska convection
this morning is a critical piece to this event as it rolls
eastward with the advancing upper trough and strong winds fields.
The question is does the convection survive all morning and push
across Lake Michigan during the mid afternoon hours. We will follow
the HREF for guidance on this. The HREF weakens the initial
convection as it moves towards or out over Lake Michigan this
afternoon. This will allow the main surge to move in this evening
out ahead of the main upper wave. If the first round of
convection survives and spreads into Lower Michigan this afternoon
that could modulate our event for the evening. We do not think
that is going to happen.

We expect the second round of storms to surge into the Lake
Michigan shoreline around 8pm. The neighborhood probabilities in
the HREF are much higher with the second round leading to our
confidence in how this event will likely play out.

The parameter space is rather high end this evening with MUCAPE
values increasing to 3,000 to 4,000 j/kg in the GFS as surface dew
points surge back into the lower 70s F. Shear values reach 40-60
knots in the 0-6km layer with the bulk of that shear occurring in
the lowest kilometer or two. HRRR hodographs this evening are
looped and large in the lowest 2-3 kilometers. HRRR Sig Tornado
Parameter values reach 4-9 this evening which is why the SPC has
placed a CIG1 conditional intensity for our entire area meaning
tornadoes may reach the EF2 level. If storms are able to remain
discrete or develop nearby a supercellular tornado threat is
possible given the CAPE/Shear balance. 850mb wind speeds will be
on the order of 40-50+ knots aiding the low level shear. We expect
discrete cells to grow upscale quickly into a linear system with
damaging winds likely. The highest tornado threat looks to be
across Western Lower Michigan, but given the dynamics in place
this evening cannot rule anywhere out of the tornado threat.
Strong damaging winds are also possible given the magnitude of the
low level jet in place. A CIG1 for wind is also in place across
the entire area meaning winds to 75 mph are possible. The entire
CWA is in an Enhanced risk by the SPC which does not happen too
often. Given the threats today...it is a day where it will pay to
be weather wise. Pay attention to possible watches this evening
and subsequent warnings.

PWAT values will surge into the 2.0 to 2.25 range this evening
making torrential rain likely. 1-2 inch per hour rates will
certainly be possible. Rainfall in the heaviest swaths this
evening could quickly reach the 1-3 inch range. Be aware that
short term flooding is very possible this evening especially for
urban areas and along small streams. Drainage systems will quickly
be overwhelmed by the high rainfall rates.

- Turning cooler behind a Sunday cold front

Another cold front is expected to move through the Great Lakes
Saturday night and Sunday. Another round of showers and storms
will accompany the front. We expect to turn cooler behind this
front with highs cooling back into the upper 60s to lower 70s.
Focus is clearly on the high end weather that is likely this
evening.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 650 AM EDT Thu Jun 11 2026

Overall the thinking has not changed in how today is expected to
progress. We have some diminishing areas of rain and some
localized lower ceilings associated with that. The rain should
taper off in the next couple hours...or through 14z. Ceiling
should lift as well with mainly VFR conditions prevailing by late
morning. VFR weather is then expected to prevail through the
afternoon.

The main item of note with this 12z set of TAFs is we are
expecting severe thunderstorms to move through the TAF sites
between 00z and roughly 05z. At this point have prevailing thunder
during that time frame but have held off on high end wind gusts
given how far out in time it still is. Storms this evening will
contain low ceilings and visibilities to IFR and lower, torrential
rainfall and the potential for winds gusts over 45 knots.

&&

.MARINE...
Issued at 414 AM EDT Thu Jun 11 2026

Have opted to issue a Beach Hazards Statement and Small Craft
Advisory from this evening through the morning hours of Friday
(through noon). The low level jet increase tonight as well as the
storms themselves should stir up the lake quite a bit. We are in
agreement with the WaveWatch3 which is indicating solid 3-6
footers up and down the shoreline. While it is still early season
and the bulk of the waves will occur overnight it is prudent to
warn mariners of the increasing wave field and swimmers especially
for Friday morning. Conditions should tone down Friday night into
Saturday on the Big Lake.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from this evening through Friday morning
     for MIZ037-043-050-056-064-071.
MARINE...Small Craft Advisory from 8 PM this evening to noon EDT Friday
     for LMZ844>849.

&&

$$

DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke