565
FXUS63 KGRR 201755
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
155 PM EDT Sun Sep 20 2026

.KEY MESSAGES...

- Rain tapers off this afternoon/evening

- Mainly dry weather is expected from Monday through Friday

- Seasonable temperatures this week...feeling more like fall

&&

.DISCUSSION...
Issued at 154 PM EDT Sun Sep 20 2026

- Rain tapers off this afternoon/evening

Precipitation is in the process of winding down this afternoon over
Southern Lower Michigan. A zone of convergence in the 850-700mb
layer is aiding the precipitation. Models show the axis of
convergence moving southward steadily this afternoon and evening.
Expecting the precipitation to come to an end by midnight. Low
clouds will also trend southward and scour out along I-94 as we move
into the late evening hours.

Rainfall of 2-3 inches has been common in the heavy rain area to the
south and southwest of Grand Rapids. Some reports in excess of 3
inches are also noted on local observation sites.

- Mainly dry weather is expected from Monday through Friday

High pressure is situated over the Great Lakes region for
essentially the entire work week. Ensemble members of both the GFS
and the ECWMF indicate mainly dry weather leading to a high
confidence forecast.

The only exception to this rule will be associated with an upper low
seen spinning eastward across the state of Wyoming today. The upper
low will work through our area Tuesday and Wednesday. At this point
we have dry weather in areas that it traverses. The thinking is that
too much dry air will be in place associated with the sprawling
surface high. We will be monitoring forecast trends, but at this
point at worst it would be a few isolated showers.

- Seasonable temperatures this week...feeling more like fall

850mb temperatures are expected to be in the single digits C this
week, which will equate to conditions feeling much more like fall.
The difference from this weekend to the upcoming work week is that
it will be much less humid. Northeast winds via outflow from
Canadian high pressure to the north will allow much drier air to
filter in. Dew points at present are around 60F in Grand Rapids. We
expect dew points to drop into the 30s and 40s F much of this week.
That is a drop in humidity that will be noticeable. Highs this
week will be in the 60s most days with lows in the 40s. For
reference, normal high/low in Grand Rapids today 72 and 51. Bottom
line...slightly cooler than normal temperatures combined with
lower humidity will make for light jacket/sweatshirt weather.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 135 PM EDT Sun Sep 20 2026

Quick break from heavier precip coming to an end in the first
couple hours of the taf period. ifr and lifr will be common in
rain at all terminals for about 4-6 hours except kmkg as precip
will stay south of there. Rain slowly moves off after 00z with
I-94 sites seeing the rain ending last. VFR conditions should
return gradually overnight. Breezy northeasterly winds move in
early Monday...though winds should generally remain below 20kts.

&&

.MARINE...
Issued at 154 PM EDT Sun Sep 20 2026

A period of stronger winds will develop this afternoon and evening
over Northern Lake Michigan especially, due to a tightening pressure
gradient. A strong high to the north advancing southward from Canada
will join forces with weak low pressure in the Ohio Valley to
increase winds to 15-25 knots from the northeast. Waves spread out
in all directions from the wind, so 3-6 footers will build into our
forecast zones up near Big and Little Sable Point`s (or areas north
of Whitehall). We currently have a Small Craft Advisory in place for
areas north of Whitehall to cover the threat of winds to 30 knots
and waves of 3 to 6 feet. The SCA runs through 200am tonight and
that end time still looks good.

A persistent area of high pressure will remain parked over Ontario,
Quebec and the Great Lakes this week which will result in a easterly
off shore wind. Waves should remain 2 feet or less this week once we
get by this evening`s higher winds.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 2 AM EDT Monday for LMZ848-849.

&&

$$

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