Glacier Point and Tioga Pass Roads Opening Dates 2019
Post date: Apr 17, 2019 5:2:41 AM
A monster snowfall two years ago (163% of average statewide) was followed by a dud (54% of average statewide). But another monster snowfall came this year. As of April 1, across California the snow totals come to 163% in the north, 165% in the central, and 155% in the south for a state-wide total of 161% for 2019 (source), which falls just shy of what was seen in 2017. For Lassen Volcanic National Park, the amounts vary from 133% on Lower Lassen Peak to 208% at Manzanita Lake (source). Yosemite is also similar at 153% and 176% for the Merced and Tuolumne drainages, respectively. Similar April 1 amounts for Yosemite occurred in 2017, 2011, 2005, 1998, 1995, and 1993 (see table below; source).
Based on these past years, the Glacier Point Road could open anytime between mid-and late-May while the Tioga Pass Road probably won't open until mid- to late-June. 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 2019's snow accumulation looks like at Ostrander Lake (STR), the best predictor of opening dates. As you can see, it was nearly a record year for this site. Again, I like looking at median (1980-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 200%. According to the median, it is 221%. Either way, these numbers are pretty impressive.The snow accumulation at Tenaya Lake (TNY) is also similar to the overall values at 172% of mean and 190% of median (1980-present). Dana Meadows (DAN) saw somewhat less snow versus the rest of the Sierras with the snowpack at 133% of mean and 143% of median (1981-present). Tuolumne Meadows (TUM) snow accumulation is more similar to the rest of range at 161% of mean and 181% of median (1980-present). Unfortunately, no data exists from Virginia Lakes (VLks) for 2019. I typically use maximum SWE values to predict opening dates, but because it is possible for maximum SWE to occur after today's date I am forced to rely on April 1 values which are less reliable. For the Glacier Point Road, DAN (44% of variability) predicts an opening date of May 22, and STR (68% of variability) predicts an opening date of June 21. Based on recent years, DAN appears to be a better predictor. For the Tioga Pass Road, TNY (77% of variability) predicts an opening date of June 16 and STR (70% of variability) predicts an opening date of June 24. Both 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 May 20 and 28 and the Tioga Pass Road will open sometime between June 16 and 24. Should these predictions prove accurate, the roads will open later than an "average" year. Glacier Point Road may be open for Memorial Day weekend but the Tioga Pass Road won't be open until well into June. Yosemite Valley waterfall volume should be peaking slightly later this year as well (~early June). 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 (4/16):
It is unclear if the snowpack is melting. It is likely that it is, but we'd have to wait another week or two to be sure. Plowing has not started yet on the Tioga Pass Road or the Glacier Point Road. Updates for both will be coming soon. 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 June 17. The other sites predict an opening between May 22-31 but are significantly weaker in predicting previous opening dates than STR. However, the predictions for these other sites correspond with more recent years. For the Tioga Pass Road, TNY (82% of the variability) is the strongest predictor of the opening date and predicts an opening date of June 17. STR (76% of variability) is the next strongest and predicts an opening date of June 21. Based on these and the April 1 values, I am going to slightly adjust my estimates for the Glacier Point Road and stick with my original predictions for the Tioga Pass Road. I estimate that the Glacier Point Road will open sometime between May 22 and 30 and the Tioga Pass Road will open sometime between June 16 and 24.