Methodology
How this forecast is built
No black boxes - every step between raw weather data and the number on the meter.
A baseline peak date per location
Every tracked place has a historical median peak plus observed peaks from recent seasons. Those are blended, weighted toward recent years, into a baseline date. This is the calendar anchor - set by day length, which weather cannot move.
Live weather, elevation-corrected
We pull daily observed and forecast temperature and precipitation for each location's actual coordinates, then apply a 3.5°F per 1,000 ft lapse correction so a ridge-top reading is not treated like a valley reading.
Shift the date
Cold nights below 45°F pull peak earlier. A warm anomaly against the seasonal normal pushes it later. Rainfall deficit since September 1 accelerates leaf drop. The result is a shift in days, usually between minus five and plus six.
Score the intensity
Vibrancy is separate from timing. Cool-but-not-freezing nights plus sunny days plus adequate soil moisture produce saturated reds. Drought and warmth produce yellows and browns. Vibrancy caps how high the color index can reach in a given year.
Build the daily curve
For each day we compute distance from the predicted peak and run it through a logistic rise, a short plateau, and a faster Gaussian decay - because leaves come on slower than they fall off. That produces the 0-100 color index and its stage.
Attach honest confidence
Confidence starts high where we have observed weather and decays with forecast distance. Peak probability widens as confidence drops, so a date three weeks out shows a wider, humbler window than tomorrow does.
Score the trip
Your trip score blends the best available color each day, peak probability, how many strong alternatives you have, and how many distinct elevation bands you can reach. A short trip on exactly the right date and a long trip spanning several bands can both score well.
What this model cannot do
- It cannot see a single wind event. One night of 50 mph gusts during peak week can strip an exposed ridge in hours.
- It works at the scale of a location, not a single tree. A sheltered north-facing cove can run a week behind the overlook above it.
- Long-range forecasts past about three weeks lean on climatology, so treat them as planning ranges rather than promises.
- It does not know about road closures. Always check park road status the morning you travel.