735
FXUS63 KGRR 180655
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
255 AM EDT Wed Mar 18 2026
.KEY MESSAGES...
- Light snow accumulations today
- Ice accumulations possible tonight and Thursday morning
- Rain chances Friday, potentially significant warmup Saturday
- Rain to snow Sat night/Sun with cooler temperatures early next
week
&&
.DISCUSSION...
Issued at 255 AM EDT Wed Mar 18 2026
- Light snow accumulations today
Water vapor imagery and roabs indicate a strong upper jet diving
southeast across the Northern Plains. Associated sharp folding of
the tropopause is allowing a narrow reservoir of upper PV to
develop over the Midwest. Upper PV advection associated with this
feature moving eastward is inducing isentropic ascent across the
Upper Midwest, and we currently see snow falling across WI in
response to this upward forcing. This region of isentropic
ascent/warm advection will spread snow across the forecast area
today with only minor accumulations expected. As noted previously,
this system is not particularly strong with respect to overall forcing
and the 18/00Z soundings from APX/DTX show a large depth of dry
tropospheric air that will take a while to moisten. Snowfall
accumulation expectations haven`t really changed...generally half
an inch or less inland with 1-2" (locally more) by the lakeshore
from Muskegon northward where low level frictional convergence
will be in play.
- Ice accumulations possible tonight and Thursday morning
Concern is growing about freezing drizzle, perhaps even light
freezing rain, on the backside of this system and with the
passage of another weak system. Latest HREF guidance paints a
large area of 0.01" to 0.1" ice accumulations over interior
Southwest Lower MI starting late tonight and ending late Thursday
morning. This is one of those sneaky events that could end up
being quite impactful for the Thursday morning commute, so
allowing extra time for travel then will likely be helpful.
- Rain chances Friday, potentially significant warmup Saturday
Another system in the flow could clip the area on Friday. This
system will be further north as upper heights will continue to rise
a bit. Much of the area will likely stay dry, with the northern
portion of the forecast area seeing the best chance of some light
rain.
The Friday system being far enough north will allow the low level
flow from the SW to become established over the area. This will be
advecting warmer air up and over the area. This flow will increase
Friday night into Saturday. We will be looking at some potentially
warm weather, depending on the timing of a front passing through the
area sometime from early Saturday through late Saturday. The later
this front moves through, the better the chance we see warmer
temperatures on Saturday. The timing is uncertain at this time, with
temps on Saturday being as low as the upper 40s and 50s, to
potentially in the 60s to near 70F.
- Rain to snow Sat night/Sun with cooler temperatures early next week
Whatever the timing of the front is on Saturday, it will become
active Saturday night into Sunday with precipitation. It is likely
to be warm enough initially to be rain, but will transition over the
snow as colder air pushes in through Sunday. Still a lot of details
to be worked out with this over the next few days.
We will then see a fairly strong Canadian sfc ridge move over the
area Sunday night and linger through Tuesday. This will bring dry
and cool conditions to the area.
&&
.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 155 AM EDT Wed Mar 18 2026
Made mostly minor timing changes regarding the onset of snow for this
TAF package. The real question is whether (or for how long) we
achieve IFR visibility restrictions. Upstream observations in WI
do indicate some visibilities in the 1-3SM range, and we might
get a bit of a boost from Lake MI. So, there is significant
potential for the just-issued TAF package to require more
pessimistic updates in terms of IFR visibility restrictions.
Ceilings will be a bit tricky as well. Upstream observations
indicate cloud bases above 2000 ft AGL even in snow, but temporary
LIFR ceiling restrictions can`t be completely ruled out this side
of Lake MI.
&&
.MARINE...
Issued at 255 AM EDT Wed Mar 18 2026
Have hoisted a Small Craft Advisory (SCA) starting later this
morning and lasting into early tonight. Made this a monolithic
single segment product even though the timing will be a bit more
nuanced than that. For example, SCA conditions will take a bit
longer to materialize farther south towards South Haven and a bit
longer to end farther north towards the Sable Points. Later shifts
can hammer out the finer details as new guidance becomes
available.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 11 PM EDT this evening for LMZ844>849.
&&
$$
DISCUSSION...TJT/NJJ
AVIATION...TJT
MARINE...TJT
NWS GRR Office Area Forecast Discussion
