With an elevation 9943 feet (3031 m), Tioga Pass is California's highest mountain pass which is open to vehicles. Situated at the eastern entrance to Yosemite National Park, the road provides the only crossing of the Sierra Nevada range for about 200 miles (320 km).
However, being at the top of the Sierras, Tioga Pass receives lots of snow every year, and the road is closed each winter. The date that the road will open each spring is dependent upon how long it takes to clear the snow from the road to make it safe for travel. The more snow there is, the later in the season it will be before the road opens.
This page compares the relationship between the April snowpack survey and the date the road opens using historical data which stretched back as far as 1980.
With record snowpack, 2023 marked the pass's latest re-opening date for all of the forty-plus years in the dataset: Tioga Pass reopened on July 22! This record is represented by the yellow dot on the scatterplot chart below. Interestingly, even though the reopening date was so late, the plot demonstrates that the reopening was not out of line because the snowpack measurement was also greatest in the data: 244% of normal*. The regression line on the scatterplot shows that July 22 actually was very close to the date that could have been expected for such a snowpack, given historical data. If anything, the regression line suggests that the road may have opened a few days early.
* The values may be historic, but the data that I have goes back only to 1980, so the 2023 snowpack and road opening are the greatest and the latest for 45 observations.
The first chart is a scatter chart which compares the April 1 snowpack percentage (100%="normal") to the date that Tioga Pass opened in that year. In general, the greater the snowpack, then the later that the pass opened. April 1 is generally regarded by hydrologists as the survey with the maximum snowpack for the season. After that date, the seasonal melting begins. That is not to say that it does not snow after that date, only that, on balance, the seasonal snowpack begins to decline after that date.
There is a second option for the chart -- it can be toggled to compare the closing date of the pass versus the prior winter's snowfall. As you can see, there is not any predictive value in that comparison.
The second chart is a Gantt chart showing the open dates and close dates each year since 1980.
Last Updated 2025-05-26
Charts, maps, and text on this page ©2020-25 by Daniel Stober. All rights reserved.
Cartography from Open Street Map and Stamen Design.
Code for Best Fit regression modified from code found here