Projected emergence: ~May 25
Something unusual is happening on Silver Creek. By April 2, the creek has already accumulated 440 growing degree days toward the brown drake hatch — more than double the ten-year average of 198 GDD at this date. If the trend holds, Ephemera simulans could emerge a full week earlier than its historical average of June 2.
This page is a real-time experiment: we're tracking our GDD-based prediction against reality, updating weekly as actual water temperature data comes in. When the brown drakes finally appear on Silver Creek, we'll know exactly how far out the model started getting it right — and where it wobbled.
GDD Climbing Toward 1,100
What Are Growing Degree Days?
Aquatic insects don't check calendars — they respond to accumulated heat. Growing Degree Days (GDD) measure the total thermal energy a river has delivered since January 1. Every day the water temperature exceeds a species' base temperature, the excess degrees are banked. When the bank hits a threshold, emergence begins.
accumulated_gdd = sum(daily_gdd) from Jan 1 to today
Brown drake: base_temp = 39°F · threshold = 1,100 GDD
For the brown drake, every day Silver Creek's average water temperature exceeds 39°F contributes to the total. In a normal year, it takes until early June to bank 1,100 GDD. In 2026, warmer-than-average winter water temperatures have the creek running roughly 8 days ahead of schedule.
2026 vs. the Decade
10-Year Emergence Record
| Year | GDD by Apr 2 | Emergence | DOY | vs. Avg |
|---|
Weekly Prediction Log
Each week we record the model's current projection. After the hatch, we'll look back and see how prediction accuracy changed with proximity — how early can you trust a GDD forecast?
What Could Change
The model isn't a guarantee — it's a best estimate from today's data. Several factors could push emergence earlier or later from here:
Cold snap or warm spell. A week of below-normal temps would slow GDD accumulation and push the date out. Conversely, continued warmth could move it even earlier — but the photoperiod gate at May 12 sets a hard floor.
Spring runoff timing. High flows from snowmelt carry cold mountain water that suppresses effective GDD. The model applies a flow suppression multiplier, but an unusually late or heavy runoff could overpower it.
Localized conditions. Silver Creek is spring-fed, which buffers temperature swings more than freestone rivers. This makes GDD predictions more reliable here than on snowmelt-dominated systems — one reason we chose this river for the experiment.