- Snow water
- The water the winter's snow has added since 1 October, as a depth: each day's rise on a snow pillow (a pad that weighs the snow on it), added up; melt does not subtract.
- Estimated snowfall
- Snow water times the snowfall ratio measured at the Central Sierra Snow Lab, shown as a range: a rough depth of new snow, not a measurement.
- Typical season
- Every winter from 1985–86 to 2025–26 (41 winters), each counted once, ignoring this winter's snow so far.
- Our main forecast
- This winter's snow so far, plus what each past winter added from the same date on: one possible outcome per past winter.
- El Niño
- A warming of the central tropical Pacific that shifts winter storm tracks; its index is the sea temperature there compared with normal. On past winters here, knowing it did not improve our forecasts.
- Outside forecast
- A seasonal forecast made by an agency other than us: NMME, SEAS5 or CPC. We show them; we do not make them.
- In snow terms
- An outside precipitation forecast turned into snow water, by giving more weight to past winters whose precipitation came closest to it. From precipitation only: temperature is not used.
- 8-in-10 range
- From the 10th to the 90th percentile of a forecast: 8 chances in 10 that the outcome lands inside it. The middle half works the same way, 1 chance in 2.
- Chance
- The weighted share of a forecast's possible outcomes, one per past winter, that reach the amount: a chance from history, not a guarantee.
- Tested on past winters (leave-one-winter-out)
- Each past winter is forecast as if it were happening now, using only the other winters, then scored against what fell.
- Correlation
- How closely past forecasts rose and fell with what happened: 1 is perfect, 0 is no relation. With about 40 winters, values below about 0.3 cannot be told apart from 0.
- Wettest, middle and driest third
- Past winters split into three equal groups by precipitation, so each has a 1-in-3 chance in an ordinary year.
- NMME
- The North American Multi-Model Ensemble: seasonal forecasts from several US and Canadian centres.
- SEAS5
- The seasonal forecast system of the European Centre for Medium-Range Weather Forecasts (ECMWF), published by the Copernicus Climate Change Service.
- CPC
- NOAA's Climate Prediction Center. Its forecasters publish official outlooks for three-month periods, written here as month ranges such as Nov–Jan, as odds for each third.