640
FXUS63 KGRR 152349
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
749 PM EDT Mon Sep 15 2025
.KEY MESSAGES...
- Areas of Fog and Low Clouds Across Central Lower Michigan Tonight
- Dry And Warm Through Friday
- Showers Possible This Weekend
&&
.DISCUSSION...
Issued at 307 PM EDT Mon Sep 15 2025
- Areas of Fog and Low Clouds Across Central Lower Michigan Tonight
Forecast soundings and persistence of the synoptic pattern suggest
that tonight will be similar to this morning in terms of fog and low
stratus development. Easterly flow will advect low-level moisture
off of Lake Huron which will be trapped under the nocturnal
inversion. Cannot rule out some locally dense fog similar to this
morning, but that is not expected to be widespread. Any fog and
stratus that develop will burn off in the hour or two after sunrise
as the sun angle is still decently strong.
- Dry And Warm Through Friday
A Rex block pattern transitioning into pure large scale ridging is
expected through Friday. This will keep conditions generally dry
with one possible exception. A cold front is forecast to sink
through the area Thursday into Thursday night. Some guidance such as
the ECMWF/EPS wants a few showers to develop off of that front near
US10. However, moisture quality looks to generally be poor with
frontal passage so will keep rain chances in the 10-20 percent range
across the US10 corridor. Highs will be in the mid to upper eighties
areawide through Thursday before cooling some for Friday behind the
cold front.
- Showers Possible This Weekend
Still a lower confidence scenario in forecast evolution Saturday
into early next week. The going forecast favors a bit of a cooldown
during this period as large scale troughing, possibly as a cutoff
low, moves into the region. However with the weak flow aloft
persisting, this brings into question how this low evolves and
tracks. This troughing may lead to one or more periods of shower
development this weekend into early next week. However between the
relatively modest nature of the mid-level height falls, and poor
moisture quality given the lack of a connection to the Gulf, any
rainfall would be light.
&&
.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 749 PM EDT Mon Sep 15 2025
We are expecting some shallow ground fog to develop in spots
tonight, similar to last night. Last night both AZO and JXN had
visibilities dip below VFR between 09z and 12z. Given no airmass
change we expect a persistence forecast to likely work again. Like
last night as well, we will see some stratus and fog develop
across Central Lower Michigan towards daybreak. Otherwise VFR
weather will be the rule with high pressure firmly situated across
the area. A light northeast to east wind will continue.
&&
.MARINE...
Issued at 307 PM EDT Mon Sep 15 2025
No change to the overall pattern in the Great Lakes for this week
when looking at the latest model guidance. Surface ridging and/or a
slack pressure gradient will insure that we see waves of 2 feet or
less through the end of the week.
The next time frame that the wind picks up will occur on Friday when
easterly winds freshen as stronger high pressure settles into the
Great Lakes from the north. Even in that regime though with an off
shore wind of 15 to 25 knots waves will remain low given limited
fetch. Bottom line...some great end of season boating weather.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Thomas
AVIATION...Duke
MARINE...Duke
NWS GRR Office Area Forecast Discussion
