630
FXUS63 KGRR 061710
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
110 PM EDT Mon Oct 6 2025

.KEY MESSAGES...

- Cold front brings rain by this evening

- Frost/Freeze conditions for mid-week

&&

.DISCUSSION...
Issued at 210 AM EDT Mon Oct 6 2025

- Cold front brings rain this evening

Height falls occur on today as the upper ridge shifts east with
low level moisture increasing ahead of an advancing western CONUS
trough, with deep moisture streaming up from the Gulf. A cold
front is expected to focus showers and a few thunderstorms this
evening into Tuesday morning.

Instability is limited but forecast wind profiles show 30 knots of
unidirectional deep layer shear and suggest linear convection is
possible along/ahead of the front this evening. This is supported
by the hi-res models with the FV3 and ARW showing convection
forming into line segments, which could contain brief heavy
downpours and gusty winds, even if they are low topped and lack
thunder. The front clears Lower Michigan on Tuesday night with
dry northerly flow as high pressure builds in.

- Frost/Freeze conditions for mid-week

As the climatological end of the growing season approaches this
week, we will see frost by Wednesday morning with a better chance
for frost and freezing conditions Thursday morning as the surface
ridge axis moves across Lower Michigan allowing winds to decouple
and optimal radiational cooling conditions.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 109 PM EDT Mon Oct 6 2025

VFR expected through the rest of the afternoon with gusts to 20
knots at Muskegon. A cold front arrives this evening with showers
and low stratus expected. Have added a PROB30 for TSRA for the
most favored window for thunder potential this evening based on
short range model guidance, with gusty winds in excess of 30 knots
and heavy rain possible in any heavier showers or thunderstorms.
IFR and possibly LIFR conditions develop overnight as ceilings
fall, with these conditions persisting into the start of Tuesday
Slow improvements then begin over the course of the morning and
early afternoon.

&&

.MARINE...
Issued at 210 AM EDT Mon Oct 6 2025

Winds and waves are running lower than the current forecast, so
some adjustments have been made to match the current obs. The SCA
was dropped south of Grand Haven. Winds should continue to
decrease overnight as the front approaches and the surface
pressure gradient relaxes.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for
     LMZ847>849.

&&

$$

DISCUSSION...Ostuno
AVIATION...Thomas
MARINE...Ostuno