Ada, Michigan Weather Forecast Discussion

659
FXUS63 KGRR 200809
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
Issued by National Weather Service Detroit/Pontiac MI
409 AM EDT Sat Sep 20 2025
.KEY MESSAGES...
-Pattern Change is Underway
-Chances for Thunderstorms Tonight through Sunday Night
&&
.DISCUSSION...
Issued at 406 AM EDT Sat Sep 20 2025
-Pattern Change is Underway
Southwest Lower Michigan has had mainly clear skies, very little
precipitation the last 7 to 10 days and temperatures either 80 or
into the 80s. These conditions will not continue as we expect plenty
of clouds, showery weather and cooler readings over the course of
the next 5 days at least.
Upper ridging is in the beginning stages of breaking down and moving
east early this Saturday morning with an upper shortwave trough
moving in from the west. We will see southwest flow take over for
the weekend aloft as upper troughing moves our direction from the
Plains states. By Monday, an upper trough will be situated overhead
which should trend towards an upper low by mid week. We will see
showery weather develop as early as this evening which should
continue into Wednesday. 5 day qpf totals look to be in the 0.50 to
1.00 range with higher amounts possible toward I-94.
Temperatures which have been well above normal will quickly cool
with the clouds and precipitation of the next 5 days or so. Highs
will be close to normal in the lower 70s much of the 7 day forecast.
-Chances for Thunderstorms Tonight through Sunday Night
Surface dew points will continue to creep up today through Sunday,
peaking on Sunday as we move into southwest flow. MUCAPE values both
this afternoon and evening and again Sunday afternoon and evening
push to around or slightly above 1,000 j/kg. PWAT values increase to
around 1.5 inches which is above the 90th percentile for
today/tomorrow. Bottom line there will be a moisture surge into the
forecast area. That low level moisture when combined with an upper
shortwave this evening and again on Sunday should yield embedded
thunderstorms within a larger precipitation shield. We are in the
Day 2 (Sunday) Marginal SPC outlook for severe weather. Agree with
that assessment as there is a surge in the 850mb low level jet in
all of the high res models. The NAM looks to be the most bullish,
but we will likely see winds at that level increase to 20-30 knots.
The HREF shows some embedded thunder this evening after 00Z across
Western Lower Michigan and then once again over much of the area
Sunday afternoon and evening. Deep layer shear is forecast to
increase to 30+ knots Sunday so cannot rule out some isolated
marginal wind/hail in the stronger storms near max heating.
&&
.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 124 AM EDT Sat Sep 20 2025
Lingering upper level ridge over Lower Michigan with persistent
deep column dry air will result in prevailing VFR conditions
throughout tonight and early Saturday. Geopotential height falls
from upstream troughing and synoptic scale warm advection will
broaden into the state after 21z Saturday, yielding precipitation
chances between 30-70%. Introduced a TEMPO group for all taf sites
between 2z-6z.
&&
.MARINE...
Issued at 406 AM EDT Sat Sep 20 2025
Winds remain elevated at both the shoreline observation stations as
well as the buoys. Wind gusts continue to exceed 20 knots as of
300am. Given the short fetch however in an easterly flow wave
heights remain in the 1-3 foot range given the short off shore
fetch. The Small Craft Advisory in the northern 4 zones (Holland
northward) through 800am still looks good and remains unchanged.
Winds are expected to diminish towards daybreak as the gradient
slackens. We are not expecting advisory level winds or waves beyond
early this morning as weaker pressure gradient should remain in
place the next few days. Winds and waves may become briefly elevated
in and near thunderstorms however from this evening through Sunday
evening.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 8 AM EDT this morning for LMZ846>849.
&&
$$
DISCUSSION...DUKE
AVIATION...CB
MARINE...DUKE

NWS GRR Office Area Forecast Discussion