981
FXUS63 KGRR 150800
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
400 AM EDT Wed Oct 15 2025

.KEY MESSAGES...

- Rain ends this morning

- Unsettled weather for the weekend

- Temperatures rise into Saturday

&&

.DISCUSSION...
Issued at 400 AM EDT Wed Oct 15 2025

- Rain ends this morning

An area of warm advection rain is spreading across the Great Lakes
this morning. Visibilities have not budged from 10 miles which is
indicative of its light nature due to the fact it is falling from
a mid deck of clouds between 6,000-10,000 feet. RAP soundings
show considerable dry air below about 750mb. The rain is being
produced from a mid level shortwave working through the area and a
zone of 850mb moisture transport aided by a weak low level jet to
our southwest over Wisconsin. We expect the rain to continue
until around 800am at which time it should erode and come to an
end. There is still some weak moisture transport through 11am, so
its conceivable some very light returns may continue through that
time. The midday and afternoon hours will be dry with increasing
sunshine as the clouds erode.

Benign weather is expected due to the influence of expansive
surface high pressure which is expected over the Great Lakes
region from this afternoon into Thursday night. There is the
potential for some frost tonight along the U.S. Highway 127
corridor, but at this point it looks too marginal for a headline.
Coordinated with DTX and we have decided no headline at this point
with lows in the upper 30s for the most part.

- Unsettled weather for the weekend

The weekend weather is the focus of the short term with upper
ridging being replaced by a deep upper trough. Warm air advection
will be in full swing as we head from Thursday night into
Saturday. Low pressure in the plains on Friday will move to
Wisconsin/Illinois on Saturday. A cold front is expected to sweep
through the area Saturday night. PWAT values are forecast to
increase to around 1.5 which is right at the max value for
Saturday per the SPC sounding climo site for DTX. Suffice it to
say the atmosphere will have significant moisture for this time of
year. We expect showers to form as early as Thursday night into
Friday on the initial warm front with much higher chances for
precipitation Saturday into Saturday night along and ahead of the
cold front. Expecting at least 500-1000 j/kg MUCAPE values so
embedded thunderstorms are expected. The MUCAPE will be aided by
surface dew points that will rise into the lower 60s Saturday
evening.

Model disparity develops on Sunday with various solutions occuring
with regard to placement and depth of a secondary low that
develops beneath the upper trough. The GFS has a 984mb surface
low Sunday, while the ECWMF is around 995mb. Sunday looks to be a
blustery day with the jury still out on the amount of rain around.

- Temperatures rise into Saturday

Temperatures will be more seasonal today and Thursday with highs
in the 60s. We rise into Saturday as deep southerly flow takes
hold and increases in strength. Our warmest readings in the 7 day
forecast should occur on Saturday when low to mid 70s are possible
across Southern Lower Michigan. Colder air filters in behind the
low with highs in the 50s to around 60 for Sunday and Monday.



&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 149 AM EDT Wed Oct 15 2025

Light rain is moving through Southwest Lower Michigan at 06z. The
rain is quite light and VFR weather is occurring at all
observation sites. The rain is falling from a mid deck of clouds
in the 6,000-10,000 foot range. We do not envision visibilities
being affected or lowered by the rain. We also feel ceilings will
remain at or above 6,000 feet. The rain will end around 12z across
the area and ceilings will slowly begin to rise. By mid afternoon
we expect clearing to take place. VFR weather is forecast
throughout the entirety of this TAF period...06z to 06z. Winds
will generally be from the north to northeast at 10 knots or less.

&&

.MARINE...
Issued at 400 AM EDT Wed Oct 15 2025

High pressure is settling into the Great Lakes region at this time
from the north. This high will remain in place through Thursday so
winds and waves will remain below advisory levels. We did reach
advisory levels this past evening as the gradient tightened for a
short time. Winds reach the 20-25 knot level in spots and waves
increased to around 4 feet. Those conditions have subsided some
and we expect much calmer conditions into Thursday night.

Thursday night, the high will be sliding off to the east with low
pressure approaching from the plains. The gradient tightens on
Friday and reaches a maximum Friday night. We are expected at
least Small Craft Advisory conditions to develop late Thursday
night and persist into Friday and Friday night. The highest waves
in south flow will be found in our northern zones, or north of
Holland. Waves look to peak in the 4-8 foot range Friday night.
There is some potential for gales Friday night.

The evolution of the weekend pattern is not certain, but an even
higher wind/wave event is possible on Sunday as a secondary low
develops beneath the deep upper trough. Gales and waves around 10
feet may occur.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke