189
FXUS63 KGRR 172259
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
659 PM EDT Sat Oct 17 2026
.KEY MESSAGES...
- Areas of frost tonight
- Warming trend with fair weather
&&
.DISCUSSION...
Issued at 153 PM EDT Sat Oct 17 2026
- Areas of frost tonight
Saturday morning temperatures away from Lake Michigan were right
around 32 degrees, plus or minus a few degrees locally, with
areas of frost as expected. A more marginal setup for frost is
expected tonight, mostly in southern Michigan. As the surface high
pressure ridge migrates southeast of Michigan tonight, low-level
southwest flow will increase to 15-25 knots. While the surface
layer should decouple under strong radiational cooling, the
increasing pressure gradient winds may keep some locations stirred
up enough to prevent widespread frost. Model guidance on
overnight lows tonight remains a few degrees higher compared to
last night. The frost advisory for southern Michigan, where winds
will be relatively weaker, will be the final one issued from the
GRR WFO until spring.
- Warming trend with fair weather
The brief shot of cooler air is already exiting, to be replaced by
a warmer mix of Pacific and Southwest continental air. 925-850 mb
temperatures between this morning and Sunday morning will rebound
about 10 degrees C and remain that way for several days. After a
breezy Sunday, calmer winds are favored much of the coming week
under weak upper-level flow and a tendency for subsidence and high
pressure over the region. Normal high temperatures are now around
60 degrees, and the next several days will feature highs trending
from the lower to the upper 60s. Ensembles are in good agreement
regarding the forecast temperatures and drier conditions through
at least midweek.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 659 PM EDT Sat Oct 17 2026
No significant changes to the forecast this evening, clear skies
and no visibility restrictions are expected given high pressure
and a dry airmass across the region. Gusts to 20-25 knots are
likely at MKG through the night, and at GRR and LAN beginning mid
morning Sunday as diurnal mixing kicks in. LLWS approaches 30
knots from approx. 06z-13z tonight as a low-level jet sets up near
2kft, however winds likely remain elevated enough to keep below
inclusion thresholds. Expect predominantly southwest flow through
the TAF period.
&&
.MARINE...
Issued at 153 PM EDT Sat Oct 17 2026
Deteriorating conditons are expected today into tonight, becoming
increasingly hazardous for small craft from north to south, as
southwest winds strengthen and waves build. An upgrade to a gale
warning Sunday morning is possible for the nearshore near Big and
Little Sable Points (north of Whitehall), as 25 to 30 knot winds
could gust up to 35 knots.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Frost Advisory from 3 AM to 8 AM EDT Sunday for MIZ064>067-
071>074.
MARINE...Small Craft Advisory until 11 PM EDT Sunday for LMZ844>846.
Small Craft Advisory until 11 PM EDT Sunday for LMZ847>849.
&&
$$
DISCUSSION...CAS
AVIATION...Thomas
MARINE...CAS
NWS GRR Office Area Forecast Discussion
