Microseason 70 of 72 · December 16–20
Ice begins to form at the edges
A five-day window of the year, read through nine North American climate regions.
Same week, nine climates
A microseason names a five-day window of the solar year. What that window actually looks like on the ground depends on where you are. Below, the same calendar window read through each of nine North American climate regions.
- NENortheast Continental
Ice begins to form at the edges
Shallow ponds and puddles ice over on cold, windless nights.
- SESoutheast Subtropical
Ice Edges Deepen Inward
Shallow ponds and swamp margins freeze solid. Shad and striped bass retreat to deeper channels in rivers draining the Appalachians. Water temperatures in the 30s limit all movement.
- PNWPacific Northwest
Ice forms at the margins
Silver thaw cycles increase. Freezing rain followed by mild days melts ice, refreezes at night. Alpine lakes freeze solid. Creek slush thickens.
- CACalifornia Mediterranean
Winter salmon runs peak in northern rivers
Chinook and coho salmon surge upstream in peak December flows; redwood and Douglas fir groves rim spawning gravels.
- MWMountain West
Ice thickens across frozen water
Lakes and ponds are sealed beneath thickening ice. Rivers form shelves and caps, with only the fastest water remaining open to the winter air.
- MPPlains Continental
Rivers turn to stone
The Missouri and Mississippi lock solid. Walleye and catfish enter torpor in deep holes. Ice thickness reaches one foot across prairie lakes.
- SWSouthwest Desert
Solstice stillness settles
The winter sun stops its retreat; daylight begins—infinitesimally—to return. The desert holds perfect stillness, waiting.
- TRTropical / Sub-Tropical
The sun turns again
Solstice passes. Sun begins slow northern ascent. Water temperature stabilizes at annual minimum. Holiday season peaks across the region.
- AKAlaska Subarctic
Ice thickens through solstice week
Days begin lengthening imperceptibly. Ice reaches maximum thickness. Freeze-up is complete everywhere. Land locked in place.
About the 72-microseason calendar
A microseason is a five-day window of the solar year — long enough to notice something change, short enough that the change is specific. The year holds seventy-two of them, six per month, ordered by what the natural world is doing rather than what the clock says. Almanac calendars like this are an old American habit, kept by farmers, gardeners, and birders for centuries; Weather Story collects them into a single reference.
Each microseason is read through nine North American climate regions. The phenological events that mark a five-day window vary with ecology — the strawberries that open in the Northeast might coincide with the first magnolias dropping in the Southeast and the salmonberry blossoms unfurling in the Pacific Northwest. Same week, nine ecologies, nine readings.