010
FXUS63 KGRR 131900
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
300 PM EDT Sat Jun 13 2026
.KEY MESSAGES...
- Scattered Storms This Evening and Tonight
- Cooler Sunday with Morning Showers
- Wet Midweek Period Likely
&&
.DISCUSSION...
Issued at 259 PM EDT Sat Jun 13 2026
- Scattered Storms This Evening and Tonight
As of early afternoon, thunderstorms have developed across north
central and NE Lower MI ahead of a cold front that is
approximately located across far NE WI and into the central U.P.
The environment in this region features 1500-2000 J/kg of SBCAPE
and 60 kts of deep layer shear. The LLJ is better oriented across
northern Lower as opposed to southern Lower, where it is
divergent. Still, we believe scattered storms in the form of a
broken line may develop closer to the 21z-00z time frame over
central Lake Michigan into west central Lower MI, moving southeast
into the 00z-04z time frame.
Synoptic support is certainly present tonight as mentioned in the
previous discussion. Good upper jet divergence, a solid mid level
jet of 50-60 knots, a LLJ of 30-40 kts (albeit divergent, which
is not ideal), and a surface cold front will all help the cause.
Thermodynamically speaking, our setup this evening is good but not
excellent. On the one hand, DCAPE looks pretty good at 800-900
J/kg ahead of the cold front, but MLCIN of 100-150 J/kg after 00z may
provide a bit of a stable barrier for stronger thunderstorm wind
gusts from reaching the surface. Could be a close call in certain
areas where healthy convection manages to develop, and peak
thunderstorm wind gusts of 40-60 mph seems reasonable. The 12z
CAMs have indicated somewhat of a fickle evolution to the
convection this evening, with different placements and timing of
potential storm development. All in all, this looks to be a more
localized setup with scattered storm development and not a
widespread damaging wind issue. Model soundings do support some
hail development with probably sub-severe hail being observed but
can`t rule out some quarter size hail in isolated spots. There may
be just enough 0-3 km shear and curvature to the hodograph coupled
with 0-3 km CAPE just under 100 J/kg to provide support for a weak
tornado to develop across southwest portions of the state, but
this threat is quite low.
- Cooler Sunday with Morning Showers
The cold front will be slow to move out of the region as the upper
trough doesn`t move into Lower MI until midday Sunday. As such,
expecting a cool and showery morning on Sunday with gradual
clearing from west to east. A NW breeze will also pick up during
the day with some gusts of 20-30 mph expected. Highs in the upper
60s to around 70 are expected.
- Wet Midweek Period Likely
After a dry Monday, rain and thunderstorms return to the region
midweek. The first round arrives Tuesday as model guidance is
indicating a fairly strong upper trough arriving and even going
negative tilt. A 30-35 kt LLJ (convergent this time) aims toward
our region by 18z Tuesday as a cold front becomes situated to the
west of Lake Michigan at that time. Showers and some thunderstorms
are fairly likely (60-80%) near and east of US 131 especially on
Tuesday into Tuesday evening. I wouldn`t rule out a few stronger
storms possible based on the available severe weather machine
learning guidance.
The break after Tuesday evening will be very brief as another
system will be hot on its heels for Wednesday. What`s interesting
about the Wednesday system is how anomalous the MSLP is shown by
the 12z ECMWF. It is showing a 990 mb low moving toward the MI/IN
border Wednesday night which would be a whopping 5 standard
deviations below normal for mid June. The orientation of the low
level jet looks excellent with an intense 60-70 kt core moving
into northern Indiana. That said, the best instability looks to
stay south of the state for this event. What is more likely to
occur is a fairly widespread rain with some thunderstorms. ENS
50th percentile QPF is almost an inch at GRR, so a fairly good
soaking looks to be coming later Wednesday into Wednesday night.
&&
.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 143 PM EDT Sat Jun 13 2026
Scattered cumulus this afternoon with VFR conditions though windy
with fairly stiff gusts to 25-30 kts expected, possibly topping 30
kts at times at MKG and GRR. Shower and thunderstorm chances go up
after 00z this evening. Not confident enough on location/timing of
TSRA for TEMPO groups yet but could foresee that especially for
MKG and GRR at some point. For now, PROB30 is appropriate. Some
thunderstorm gusts could exceed 40-45 knots. Cloud bases may get
close to IFR for LAN and JXN around or shortly after 12z Sunday
but will hold around 1500 ft with this issuance.
&&
.MARINE...
Issued at 259 PM EDT Sat Jun 13 2026
Winds and waves continue to be hazardous to small craft today and
beach hazards will continue especially from Grand Haven to the
north. For Sunday, a new set of Beach Hazards Statements and SCAs
will likely be needed near and south of Grand Haven with cooler NW
flow moving over the lake during the day.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 2 AM EDT Sunday for MIZ037-043-050-
056.
MARINE...Small Craft Advisory until 2 AM EDT Sunday for LMZ846>849.
&&
$$
DISCUSSION...Hoving
AVIATION...Hoving
MARINE...Hoving
NWS GRR Office Area Forecast Discussion
