Three short lines give us one small scene: a harsh morning, and a tern standing on ice. The title, "Inclement," means stormy or unpleasant weather, so we know from the start that conditions are bad. The first line, "mean morning," pushes this further. Calling a morning "mean" makes the weather sound almost personal, as if the day itself has a bad temper.
Then the poem gives us the tern, and the image feels slightly off. Terns are usually seen in motion, flying and diving over open water, so a tern sitting on ice looks stranded or out of place. The poem doesn't say how the speaker feels, but the choice of detail suggests a quiet sympathy, or at least close attention. The speaker notices the bird and lets it stand for the harshness of the day.
The mood is stark, chilly and still. With so few words and no commentary, the poem leaves a lot of white space, and that emptiness adds to the cold.