Lansing, Michigan Weather Forecast Discussion

611
FXUS63 KGRR 081111
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
711 AM EDT Mon Sep 8 2025
.KEY MESSAGES...
- Mostly dry through the work week
- Next chance of widespread rain sometime next weekend
&&
.DISCUSSION...
Issued at 334 AM EDT Mon Sep 8 2025
- Mostly dry through the work week
Confidence is increasing that just about all of the area will see
dry conditions persist at least through Friday.
High pressure currently over the area will slip east by Tuesday, and
will try to let a frontal system to our west move in on Wednesday.
This front will be becoming diffuse by the time it moves over the
area as the upper wave supporting it dampens out with long wave
ridging building out over the Plains.
This front will also not have any appreciable moisture to start
with. Any moisture it has dries up, and we only see some mid and
high level moisture move in with it. One can not rule a shower
popping up along it, combined with lake breeze convergence and such.
However, 99% of the area will stay dry.
The only real effect that the area sees post-frontal on Thursday is
a flow coming in from the east around a stronger area of high
pressure at the sfc to our north over Ontario. 850 mb temps really
do not change much from ahead of the front to post-frontal. This
will support no real change in max temps for the end of the week.
- Next chance of widespread rain sometime next weekend
The next appreciable rain chances look like they come next weekend,
although the amounts, timing, location, etc...all remain quite a bit
uncertain at this time.
What we do know is the models have been advertising a fairly strong
upper low dropping down from the NW in Canada. The track of this low
has been uncertain for the last couple of days. Now, it looks like
we may have another feature that could potentially interact with it,
and add to the uncertainty.
This feature is a warm front developing on the leading edge of the
heat dome that is going to try and expand toward the area from the
SW. This will be bumping up against the upper low coming in from the
NW. How these features interact and the timing of each of them will
ultimately determine rain chances and amounts for the area. With
considerable ensemble member spread that this scenario has (and one
would expect), a chance of rain is about all one can forecast for
now.
&&
.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 711 AM EDT Mon Sep 8 2025
Mostly clear skies rule across the terminals this morning. Fog has
not really developed at the fcst terminals, although KJXN and KAZO
had some brief BR in between observations.
Skies will remain mostly clear today and tonight, with just a few
cumulus expected to develop. With not much change in wind speed
and direction at most sites, decided to keep it simple with one
liners as the cumulus will dissipate and winds will stay generally
under 8 knots. KMKG will see a little stronger wind during the
day, and KJXN could see some of their normal "fog", so went into a
little more detail at those sites.
&&
.MARINE...
Issued at 334 AM EDT Mon Sep 8 2025
The trend over the last 24 hours has been for winds and waves to be
a notch higher than previous forecasts. Winds will start to increase
today as high pressure begins to slip east of the area. It does look
like winds and waves will be a category short of needing a SCA, and
will support moderate swim risk for the northern half of the
lakeshore.
Tuesday will see winds increase a tad more as the sfc front pushes a
tad closer. If trends continue, we will need a SCA and Beach Hazards
Statement for roughly the northern half of the lakeshore.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Frost Advisory until 9 AM EDT this morning for MIZ039-040.
MARINE...None.
&&
$$
DISCUSSION...NJJ
AVIATION...NJJ
MARINE...NJJ

NWS GRR Office Area Forecast Discussion