Forecasting
Ferry FYI forecasts estimate vehicle space, schedule delay, and tidal cancellation risk for upcoming sailings. They are meant to help you compare options, not to replace official Washington State Ferries status, route alerts, or terminal signs.
For source freshness and citation guidance, see Ferry FYI's data sources and API guide.
What goes into a capacity forecast?
- Current WSF capacity reports: when WSF reports live space counts, those numbers anchor the estimate.
- Similar past sailings: the model compares each sailing with the last 2 years of sailings on the same route, near the same time of day, and on similar days of the week.
- Recent direction-specific demand: when enough completed sailings show that one direction has become consistently busier or quieter than its established pattern, the model can adjust upcoming sailings in that direction. The adjustment fades for sailings farther in the future and is limited so a short-term pattern cannot overwhelm the historical forecast.
- Calendar patterns: holidays, seasonality, recency, and daylight all influence which historical sailings are most comparable.
- Service conditions: cancellations and major disruptions are handled separately so the forecast does not pretend a disrupted sailing is normal.
- Weather: upcoming temperature, cloud cover, wind, and precipitation can nudge the estimate up or down when historical data shows that similar weather affected traffic on that route.
A future sailing may briefly show every vehicle space available before WSF starts actively reporting capacity. Ferry FYI treats that initial all-open value as unavailable evidence instead of assuming the terminal is empty. Once live reporting begins, fresh WSF counts remain the strongest input.
When fewer than 10 percent of vehicle spaces are forecast to remain, Ferry FYI shows the forecast as full instead of displaying a specific number of spaces. The calibrated chance that the sailing will fill completely remains visible separately. Forecasts with a likely or high calibrated full risk are also shown as full.
How delay forecasts work
Delay forecasts follow the vessel, not just one terminal. If a boat is late leaving or arriving on one side of the route, that same delay carries into the next crossing for that boat.
- GPS progress: when a live vessel position matches the scheduled crossing, Ferry FYI compares the boat's progress across the route with where it should be on the schedule.
- Prior crossings: the projected delay for a future sailing starts with the previous crossing by that same vessel.
- Recovery factors: sailing length, vessel speed capability, and how full the prior crossing was can affect how quickly a boat may recover delay. Boats are never projected to depart before the scheduled time.
How tidal cancellation risk works
Tidal cancellation risk combines NOAA tide forecasts with routes where WSF has historically cancelled sailings at very low tide levels. For confirmed cancellations, Ferry FYI shows WSF's cancellation state. For future sailings that are not yet cancelled, Ferry FYI flags likely tidal cancellation risk when the predicted tide falls below the route's risk threshold.
Why confidence changes
Confidence is higher when there is recent, relevant historical data and a live WSF report, GPS match, or current tide forecast. It is lower when a route has sparse history, unusual timing, disruptions, or missing supporting data.
Leave-now timing and boarding limits
The leave-now sailing tool uses Google travel timing and Ferry FYI's estimate of when reported drive-up space reaches zero. Its adjustable buffer changes the recommended departure time, not the vehicle inventory expected when you arrive.
Booth lines, terminal parking, and reservation-aware boarding are not modeled. Leave-now results and capacity forecasts do not guarantee boarding.