673
FXUS63 KGRR 280000
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
800 PM EDT Sat Jun 27 2026
.KEY MESSAGES...
- Heat Wave Coming
- Dry Much of the Week, But Some Thunderstorms May Develop
&&
.DISCUSSION...
Issued at 219 PM EDT Sat Jun 27 2026
- Heat Wave Coming
A cooler than normal June will close out on a hot note as a pattern
change gets underway. A well-positioned building upper ridge will
set up across the Ohio Valley this upcoming week. This will push
upper heights into the mid 590s dm across Lower Michigan and send
850 mb temperatures into the 20-25C range. The kicker will be high
dew point values reaching into the mid 70s, so it will be humid and
uncomfortable.
Ensemble guidance tells the story regarding temperatures. Combining
the ECE/GEFS/CMC into a probabilistic dataset shows there is a high
likelihood (80%) for highs in the 90s to last at least 4 days
starting Monday and a 70% likelihood for at least 5 days. Some
areas away from the lake and especially east of US 131 may exceed
95 degrees at times and upper 90s are possible especially near and
east of Lansing and Jackson. These are rare temperatures for the
region and could lead to health hazards for outdoor workers and
those without air conditioning. Max heat index readings are very
likely to get into the 100-105 range with 105-110 possible. Heat
Advisory criteria is a heat index of 100 or greater with Extreme
Heat Watch/Warning issued for 105 or greater (or 4 days or more in
a row of 100 or greater). Heat headlines will be needed for much
of this upcoming week.
Southwest surface flow will ensure our lakeshore region stays cooler
given Lake Michigan is currently in the 60s. Even there, highs of 85
or warmer may still occur but that is tolerable compared to inland.
The broader zone of some lake-modified air is likely to be near and
north of Muskegon. NBM temperatures and dew points (low 90s/mid 70s
respectively) in this region may be overdone so we will have to fine
tune with time.
The NWS Heat Risk factors in forecast temperatures and humidity with
respect to climatology, the duration of heat (eg. is it 1 day? 3
days? 5 days?), and also known thresholds that pose an elevated risk
for heat illnesses. The four categories are Minor, Moderate, Major,
and Extreme. The current NWS Heat Risk brings the region into the
Major to Extreme categories, so impacts are likely especially given
we haven`t had much heat to deal with this year. Now is a good time
to consider modifying the scope and duration of any planned outdoor
work or activities particularly Tuesday through Thursday when
temperatures will likely be the hottest and the risk for heat
illness increases due to prolonged exposure.
- Dry Much of the Week, But Some Thunderstorms May Develop
As the warm front responsible for initiating the heat moves
through the region Sunday night into Monday morning, a few showers
and possibly thunderstorms may brush the area especially near and
north of I-96. This threat should end by midday Monday and severe
weather is not expected. Beyond Monday, it will be dry far more
than it will be wet. While the Midwest will be under the influence
of a solid LLJ of 40 to 50 kts at times, it is angled toward
MN/WI and the Upper Peninsula. Slight buckling of the LLJ at times
toward Lower MI is shown by some guidance and given the wealth of
MUCAPE available (3000-5000 J/kg) can`t rule out a ridge riding
MCS trying to dive toward our better instability during the
nighttime and early morning hours. However, there is currently not
much support for this scenario. By the end of the week, some
breakdown in the upper ridge may occur as well as a reorientation.
This may allow for some shortwave impulses to traverse the region
and increase the risk for some showers and thunderstorms to
develop Friday into Sunday. That said, some ensemble guidance (ie.
ECE members) do support a continuation of heat and humidity right
into the holiday weekend along with largely dry conditions.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 800 PM EDT Sat Jun 27 2026
VFR conditions will prevail through Sunday afternoon. Winds will
be generally from the east blo 10 knots.
&&
.MARINE...
Issued at 219 PM EDT Sat Jun 27 2026
Monday into Tuesday will feature an increasing risk for hazardous
waves both to boaters and beachgoers especially near and north of
Muskegon, where 3 to 5 feet will be possible. Small Craft
Advisories and Beach Hazards Statements are a distinct possibility
from Monday afternoon through Tuesday.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Hoving
AVIATION...Ostuno
MARINE...Hoving
NWS GRR Office Area Forecast Discussion
