Tustin, Michigan Weather Forecast Discussion

789
FXUS63 KGRR 210803
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
403 AM EDT Sun Sep 21 2025
.KEY MESSAGES...
- Thunderstorms expected today through Tuesday
- Precipitation trends for the upcoming work week
- Near normal temperatures the next week
&&
.DISCUSSION...
Issued at 403 AM EDT Sun Sep 21 2025
- Thunderstorms expected today through Tuesday
Yesterday evening was a bit active with both SPS`s and SVR`s
issued across Southwest Lower Michigan. This occurred as a low
level jet surge occurred across the area. A somewhat similar
situation occurs today as a weak 20-25 knot LLJ increases this
afternoon as seen in the HRRR, ARW and RAP. The HREF indicates a
diurnal flare occurring after 19z today. The expectation is for
numerous showers and thunderstorms to develop after that time and
gradually fill in and move east through the late afternoon and
evening (20z to 03z). There are embedded weak shortwaves is
southwest upper flow, but the stronger shortwave arrives overnight
well after peak heating. It looks like today`s convection will be
more thermodynamically driven as well as a subtle/weak warm
frontal feature nosing in from the southwest this afternoon. SPC
has us in a marginal risk for severe weather and cannot argue
given how yesterday evening went down. Again, some marginally
severe hail and wind would be the main threats. MUCAPE values
increase to 1,000 to 2,000 j/kg largely due to the increase in low
level moisture.
There will be some carryover of activity into the overnight as
well as a stronger shortwave moves our direction from the west
tonight.
- Precipitation trends for the upcoming work week
The week looks to remain unsettled weather wise as an upper trof
digs into the Great Lakes from the northwest. By Thursday, the
ECWMF has an upper low situated overhead. Showery weather that
will be diurnal in nature (highest activity in the afternoon and
evenings) can be expected. There will be enough residual moisture
around Monday and Tuesday where both showers and thunderstorms are
possible. There is model disparity between the operational GFS and
ECWMF late in the work week with the placement of a surface low.
The ECWMF has the low much further north into our area, while the
GFS is further south into the Ohio Valley. Leaning towards the
ECWMF as this point.
- Near normal temperatures the next week
Normal temperatures over the next 7 days trend from highs in the
lower 70s today to the upper 60s by next weekend. High
temperatures the next 7 days will generally by in the 70s, so we
are close to normals. Highs in the 80s can still occur this fall,
but they are not likely this week.
&&
.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 217 AM EDT Sun Sep 21 2025
Showers and a few embedded thunderstorms continue as of 06z across
Southwest Lower Michigan. We expect these showers and storms to
gradually fade through the remainder of the night as instability
continues to erode. For the most part we expect VFR weather
through daybreak, but we cannot rule out a pocket of MVFR
conditions associated with the precipitation.
During the daylight hours of Sunday, instability will build once
again with showers developing between 15z and 19z. After 19z, we
expect showers and storms to become numerous in the heat of the
day. Outside of the showers and storms, VFR weather will prevail.
East winds of 5-15 knots early this morning will veer to the
southeast and south-southwest through the course of the day.
&&
.MARINE...
Issued at 403 AM EDT Sun Sep 21 2025
No headlines are in effect early this Sunday morning and none are
anticipated over the next few days. This is the time of year when
Lake Michigan can become quite active, but that is not the case
over the next few days. The gradient does increase into Wednesday
when we will have surface high pressure off to the north and a low
to our south. This will set the stage for an increasing northeast
wind, but given the off shore nature of that flow not expecting
big impacts. Bottom line, the next few days will be relatively
calm on the big lake.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke

NWS GRR Office Area Forecast Discussion