Winn, Michigan Weather Forecast Discussion

506
FXUS63 KGRR 051744
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
144 PM EDT Sun Oct 5 2025
.KEY MESSAGES...
- Warmth gives way to increasing chance of rain by late Monday
- Frost/Freeze conditions for mid-week
&&
.DISCUSSION...
Issued at 141 AM EDT Sun Oct 5 2025
- Warmth gives way to increasing chance of rain by late Monday
Upper ridging and southwest flow persists today into Monday with
850 mb temps around 14-15C and highs in the 80s. Winds will pick
up today as surface pressure gradient tightens. Height falls occur
on Monday as low level moisture return increases 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 Monday 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 Monday evening. The front
clears Lower Michigan by 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.
&&
.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 144 PM EDT Sun Oct 5 2025
As has been the case for most of the last couple of weeks, VFR
conditions will rule for the next 24 hours.
At the beginning of this forecast period, we have some cumulus
clouds based around 6k ft agl developing inland, with a few wisps
of cirrus overhead. This will continue to be the case through
sunset. Some wind gusts to around 25 knots will also be present
this afternoon before diminishing.
Skies will go mostly clear after sunset with winds diminishing as
the atmosphere decouples. We are looking at a 30-35 knot wind core
moving in around 2-3k ft toward midnight. This is not usually
quite enough to mention low level wind shear in the forecast, but
it is good to mention here. KMKG will likely see the winds pick up
as this wind core arrives near the warmer lake.
Winds will pick up at the sfc by 16z or so as diurnal mixing takes
place. Clouds will increase at the NW sites as the cold front will
approach there late in this forecast period, and just after it.
Have mentioned BKN070 at KMKG and KGRR to account for that.
&&
.MARINE...
Issued at 141 AM EDT Sun Oct 5 2025
Winds and waves will be hazardous to small craft through Monday. A
cold front will move through MOnday night into Tuesday morning
with the potential for a few lightning strikes, then north winds
will increase Tuesday afternoon as high pressure builds in, with
some gusts over 20 knots during the afternoon and evening.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Monday afternoon for MIZ037-043-
     050-056-064.
MARINE...Small Craft Advisory until 5 PM EDT Monday for LMZ845>849.
&&
$$
DISCUSSION...Ostuno
AVIATION...NJJ
MARINE...Ostuno

NWS GRR Office Area Forecast Discussion