It isn't truly warm, but to usher in spring on the equinox:
"Spring Thunder"
Mark Van Doren - 1894-1972
Listen. The wind is still,
And far away in the night—
See! The uplands fill
With a running light.
Open the doors. It is warm;
And where the sky was clear —
Look! The head of a storm
That marches here!
Come under the trembling hedge—
Fast, although you fumble. . . . There! Did you hear the edge
Of winter crumble?