Firehole River At Old Faithful, Ynp
Firehole River · Rockies · USGS gage 06036805
Coldwater (summer mean 15.1°C — prime coldwater).
Water
54°F
Flow
71 cfs
Air
65°F
Sky
0%
Predicted hatches · 2026-06-15
PredictedGreen DrakeDrunella spp.1.00
Predicted by conditions; no reports yet. water 12.2°C (54°F) sits in the prime band (11-15°C); peak season; 4 days sustained ≥10°C; watch midday, often cloudy.
flies: Green Drake Parachute #10-12, Cripple, Hares Ear #10
PredictedMidgeChironomidae0.32
water 12.2°C (54°F) is cooling past the prime band (1-10°C); shoulder of the season; 8 days sustained ≥0°C; watch midday, especially cold months.
flies: Zebra Midge #18-22, Griffith's Gnat, Disco Midge
PREDICTED from the first-principles model only. Report-confirmed signal (fly-shop & forum reports) is the next milestone.