Compare Departure Times When Weather Data Is Incomplete

Read across one checkpoint first

The comparison matrix holds a checkpoint constant while showing your departure and the +3, +6 and +9 hour samples. Each cell contains a weather category and that checkpoint’s local arrival clock. A color is only a shortcut to the text label; it is not a road-open or safe-driving status.

Then look down the entire route

A lower category at one summit does not establish a better full journey. Read the rest of the checkpoints and the official alerts. A sparse corridor can leave large gaps between samples, so even a complete set of checkpoint responses is not continuous road coverage.

Unknown is not the lowest category

Missing forecast periods and unavailable alert responses remain explicit. The comparison only highlights a quieter weather sample when its required inputs are available across the compared windows. A report older than ten minutes prompts a refresh and suppresses a current suggestion; this interface rule does not imply forecasts become invalid at an exact universal age.

Finish with the official road check

NWS forecasts, active alerts and observed road restrictions are different data layers. A weather comparison does not predict when a closure will end. Open the route’s state-authority links, read the restriction’s direction and scope, and check again before leaving. Exported CSV rows retain unknown states and the unverified route-wide road status.