Tioga Road opening predicted June 4th, 2025

Spring is back, the snow is melting, and I’m thinking of the mountains waking up after a long cold winter. The April 1st snowpack at Tuolumne Meadows was pretty close to average for the second year in a row. The winter rangers measured 19.5 inches of snow-water-equivalent at the Tuolumne snow course at the end of March. So, once again I’ll use the past measurements of April 1st snowpack and the corresponding year’s Tioga Pass Road opening date to try and predict this year’s road opening based on current snowpack. This simple model predicts the road should open on May 23rd this year, with a 50% chance that the actual opening date will fall between May 17th and May 29th.

Looking back at how well this model has performed over the past 7 years is indicative of how a single measurement of snowpack doesn’t capture all the factors that go into the complex operation of clearing a high mountain road for public access. The closest I’ve been was 6 days off in 2018, my first prediction year. The furthest off was during the first wave of covid in 2020 when I missed by 37 days. Last year was second worst, off by 19 days.

Interestingly, in each of the past 7 years the actual opening day has been later than I’ve predicted, never earlier. This could just be chance, or it could indicate that plowing and prepping the road takes longer now than it did in the past, for reasons unrelated to the amount of snow. Excluding 2020, the Tioga Road has opened an average of 13 days later than my prediction.

So let’s just add that correction to the snow-only model prediction of May 23rd and guess that the road will actually open on June 4th, with a 50% interval from May 29th to June 10th.

*Note that the model changes every year to incorporate the newest data, so the current graph does not match up with previous years’ predictions. This is most apparent for 2023. Before that data point was established, the right side of the graph was empty. Now that we have some data there, the model can match it better.

Find raw data here: https://www.nps.gov/yose/planyourvisit/seasonal.htm and here: https://cdec.water.ca.gov/reportapp/javareports?name=COURSES

2024 Tioga Road opening date prediction

Spring has sprung, flowers are blooming, and my thoughts turn to when I’ll be able to drive through Yosemite and see Tuolumne Meadows again!

This year the April 1st measurement of snow water equivalent (SWE) in Tuolumne Meadows is 19.9 inches. My model of the Tioga Road opening date as a function of SWE predicts that the road will open on May 22 this year, with a 50% chance that the actual opening date will fall in the May 16 – 28 range.

This year’s prediction is a full 2 months earlier than when the road opened last year, July 22nd.

As before, I’ve excluded a bunch of years (grey dots and numbers on the graph) because of various management and Park operations issues. So the model and reported averages are all based on the black dots and years only.

Snow data here: https://cdec.water.ca.gov/reportapp/javareports?name=COURSES.202404

Tioga Road opening dates here: https://www.nps.gov/yose/planyourvisit/seasonal.htm

2023 Tioga Road opening prediction

It’s that time of year again to guess when the Tioga Road will open!

The 2023 Tioga Road opening date prediction is July 8th,

with a 50% chance that the real opening date will fall between June 30th and July 17th.

This is based off of the WHOPPING 62.5″ of snow water equivalent measured at the Tuolumne Meadows snow course for the April 1 report.

This huge winter has presented many challenges, this prediction included. For the first time since I started this in 2018 I need to extrapolate, to make a prediction outside of the range of existing data. I’ve ditched the linear model, since it doesn’t make sense that added inches of Apr 1 snow will have the same effect on road openings from May to July. As a snowpack lingers into June, those extra inches will melt away much faster than they did in April and May. So, I switched to a Gompertz function that has a lower and upper asymptote, which seems like a much better model for how snowpack affects getting a road open.

Snow data here: https://cdec.water.ca.gov/reportapp/javareports?name=COURSES

Past Tioga Road opening dates here: https://www.nps.gov/yose/planyourvisit/seasonal.htm

Data excluded from the model are the grey dots and dates on graph: 1995 and earlier, due to significantly different wilderness and safety regulations; 2020-2022 due to covid impacts to Park staffing and operations.

I’ll post the R code to Github if anyone wants it.