Glacier Point and Tioga Pass Roads Opening Dates 2018
Post date: Apr 14, 2018 10:33:43 PM
After last winter's monster snowfall (163% of average statewide), this year was bound to be a disappointment. Overall, it didn't end as bad as it could have been (see below). As of April 1, across California the snow totals come to 46% in the north, 61% in the central, and 52% in the south for a state-wide total of 54% for 2018 (source). For Lassen Volcanic National Park, the amounts are a little greater at 69%. Yosemite is also similar at 61% and 67% for the Merced and Tuolumne drainages, respectively. Similar April 1 amounts for Yosemite occurred in 2013, 2003, 2001, 1992, and 1981 (see table below; source).
Based on these past years, the Glacier Point Road could open anytime between early-and late-May while the Tioga Pass Road could open in mid- to late-May. When I use the data from the nearest weather stations I get a narrower range of values. To the right is a graph of what 2018's snow accumulation looks like at Tenaya Lake (TNY). Again, I like looking at median (1999-present) values to compare what "average" looks like because the actual average or "mean" gets skewed by extreme values at the end of the season. The median represents a more realistic curve. According to the mean, this year's April 1 snowpack is at 68%. According to the median, it is 75%. These numbers could have been MUCH worse. As of February 14, the snowpack was at 20% of median (and mean), which sets a new record low for that date at this station. That means over the next month and a half there was a pretty incredible rally.The snow accumulation at Dana Meadows (DAN) is more similar to the overall Yosemite results with the snowpack at 64% of mean and 69% of median (1981-present). Tuolumne Meadows (TUM) snow accumulation is a little less at 58% of mean and 65% of median (1980-present). Ostrander Lake (STR), the best predictor of opening dates, is at 65% of mean and 73% of median (1989-present). For the Glacier Point Road, Virginia Lakes (VLks; 56% of variability) predicts an opening date of May 8, TUM (61% of variability) predicts an opening date of May 4, and STR (74% of variability) predicts an opening date of April 28. Based on previous years, TUM appears to be a better predictor. For the Tioga Pass Road, TNY (77% of variability) predicts an opening date of May 16, VLks (71% of variability) predicts an opening date of May 17, and STR (74% of variability) predicts May 14. All three show strong correlation and each's prediction correlates well with previous years with similar snowpack. Therefore, I'll use a mix of all of the stations and previous years to make my predictions.
I estimate that the Glacier Point Road will open sometime between April 28 and May 6 and the Tioga Pass Road will open sometime between May 12 and 20. Should these predictions prove accurate, the roads will open a little earlier than an "average" year. Glacier Point Road may be open for the beginning of May and the Tioga Pass Road should be open prior to Memorial Day weekend. Yosemite Valley waterfall volume should be peaking around early- to mid-May. However, this will also depend on what the weather does from now until then. Check back in a few days when I update this post with April 15 numbers.
UPDATE (4/22):
The snowpack appears to be melting. Plows have worked up to the May Lake junction on the Tioga Pass Road. No updates have been provided for the Glacier Point Road. With April 15 SWE values, STR (71% of variability) is the strongest predictor of the Glacier Point Road opening date and predicts an opening date of May 1. The other sites predict an opening between May 7-12 but are significantly weaker in predicting previous opening dates than STR. For the Tioga Pass Road, TNY (88% of the variability) is the strongest predictor of the opening date and predicts an opening date of May 14. STR (76% of variability) and VLks (74% of variability) follow TNY in strength of predictions and predict an opening date of May 17 and May 15, respectively. Based on these and the April 1 values, I am going to stick with my original predictions. I estimate that the Glacier Point Road will open sometime between April 28 and May 6 and the Tioga Pass Road will open sometime between May 12 and 20.