230
FXUS63 KGRR 290627
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
227 AM EDT Sat Aug 29 2026
.KEY MESSAGES...
- Becoming Hot and Humid
- Rain Chances Increase Tonight into Sunday
- Additional Chances for Rain and Thunderstorms Next Week
&&
.DISCUSSION...
Issued at 226 AM EDT Sat Aug 29 2026
- Becoming Hot and Humid
As high pressure shifts east today, southwest flow behind the high
will advect warmer temperatures and higher dew points. Highs today around
80 will increase into the mid 80s to low 90s by Tuesday. Dew
points will increase into the mid to upper 60s with the potential
for dew points in the low 70s on Tuesday and Wednesday. The
combination of these temperatures and dew points will result heat
index values in the 90s starting Monday. The hottest heat index
values will be Tuesday and Wednesday with most of the area in the
mid 90s. Areas toward south central Michigan may see heat index
values approach 100 Tuesday.
- Rain Chances Increase Tonight into Sunday
The low level jet causing showers and thunderstorms to develop in
eastern South Dakota and western Minnesota will gradually shift
east today. A weak 500mb shortwave associated with this
convection will move in during the late afternoon and early
evening paired with the 850mb low level jet convergence.
Instability will be limited over the area therefore expected a
weakening trend as it approaches western Michigan. Showers will
expand eastward overnight into Sunday as warm air advection and
low level convergence set up over the area. The thunder potential
will remain low into Sunday morning with the best chance for a
rumble or two toward the lakeshore. Precipitable water values will
approach 2 inches which is around the 90th percentile
climatologically for this time of year. There is the potential for
some pockets of heavier rainfall (around 2 inches) as seen in the
localized probability matched mean of the HREF. The probability
looks higher toward the lakeshore as there will be a little more
instability to tap into (around 500 J/kg).
Most of the rainfall is expected Sunday morning with a lull during
the afternoon. Areas toward US-10 could see rain all day. An
additional round of rain and thunderstorms is expected to develop
Sunday night into Monday morning with the low level jet
convergence and warm air advection.
- Additional Chances for Rain and Thunderstorms Next Week
Forecast confidence decreases into next week as details get a
little murky. Slight differences in the strength and placement of
the upper level ridge and shortwave troughs moving through will
impact our chances. With the mentioned high dew points and
precipitable water values, it won`t take much to spark off showers
and thunderstorms. Therefore there are chances each day, although
the best chances will be during the overnight timeframes matching
with the best low level jet convergence and warm air advection.
&&
.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 226 AM EDT Sat Aug 29 2026
VFR conditions are expected into Saturday night with winds
becoming more southwesterly. Showers will slowly move in from the
west late this afternoon into Sunday. MKG may see these showers
prior to 6Z hence the PROB30 group toward the end of the TAF.
&&
.MARINE...
Issued at 226 AM EDT Sat Aug 29 2026
Southwest winds of 10 to 20 knots are expected today and will
build to 15 to 25 knots Sunday. This will cause wave heights of 1
to 3 feet today to increase to 2 to 5 feet for Sunday with the
highest waves north of Grand Haven. Winds may end up being lower
as there is some uncertainty if higher gusts will be able to mix
down with the warmer air moving over the waters. Highest busts may
be right along the lakeshore vs over the open waters. Southwest
winds continue into next week with wave heights remaining largely
in the 1 to 3 foot range until Tuesday.
A few thunderstorms are possible this late this afternoon into
Sunday with better chances Sunday night into Monday morning north
of Grand Haven. Daily chances for showers and storms exist through
next week, most during the overnight timeframe.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...RAH
AVIATION...RAH
MARINE...RAH
NWS GRR Office Area Forecast Discussion