This freezing degree day plot provides a crude guideline for potential frazil ice problems on the
lower Kenai River.  Phase 1 freezing degree days (FDD) are accumulated for Soldotna.  Phase 2 FDD
are calculated only when daily minimum temperatures drop below 0 deg. F.  While daily Tmin < 0 F,
Phase 2 FDD accumulate and Phase 1 FDD remain constant.  Once the Tmin > 0 F, the accumulated
Phase 2 FDD are added to Phase 1 FDD.  Phase 2 FDD are then reset to zero.

Soft guidance thresholds are provided to alert for the possibility of frazil ice jams.  Sufficient
cooling of the river (Phase 1) is required before a cold outbreak (Phase 2) can cause significant
frazil ice development.

For more information review the following presentation:

Forecasting Frazil Ice Jams on the Kenai River