Madison River Near West Yellowstone
Madison River · Rockies · USGS gage 06037500
Trout (marginal) (summer mean 20.2°C — trout, warm in summer).
Water
72°F
Flow
370 cfs
Air
73°F
Sky
5%
Predicted hatches · 2026-06-16
PredictedHexagenia (Hex)Hexagenia limbata0.87
Predicted by conditions; no reports yet. water 22.1°C (72°F) sits in the prime band (19-23°C); peak season; 2 days sustained ≥18°C (wants 3); watch after dark — the famous night hatch.
flies: Hex Dun #4-8, Hex Nymph, Hex Spinner
PredictedSlate Drake / IsonychiaIsonychia spp.0.32
water 22.1°C (72°F) is cooling past the prime band (16-21°C); shoulder of the season; 5 days sustained ≥14°C; watch afternoon/evening; nymphs crawl to shore to emerge.
flies: Isonychia #10-12, Slate Drake, Leadwing Coachman
PredictedLight CahillStenacron / Stenonema0.30
water 22.1°C (72°F) is cooling past the prime band (16-20°C); peak season; 4 days sustained ≥15°C; watch dusk.
flies: Light Cahill #14-16, Cream Cahill, Cahill Spinner
PREDICTED from the first-principles model only. Report-confirmed signal (fly-shop & forum reports) is the next milestone.