textproduct: Grand Rapids

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 /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 658 AM EDT Wed Mar 18 2026

Main change was to bring onset of snow to MKG earlier. Surface observations show winds backed to the southeast along the lakeshore, presumably due to land breeze effects. This has resulted in isentropic ascent thanks to southwest flow just off the deck. Light radar reflectivities are overspreading much of southwest Lower MI, but ceilings inland are still very high, indicating a deep, dry lower troposphere to overcome.

Besides introducing snow to MKG earlier, delayed onset of snow at other terminals based on current trends.

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.