2019-2020 Annual Report Bridgeport Winter Recreation Area
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2019-2020 Annual Report Bridgeport Winter Recreation Area Report to Jan Cutts, District Ranger Bridgeport Ranger District, Humboldt-Toiyabe National Forest INTRODUCTION The purpose of the 2020 Annual Report is to establish a baseline document to guide future end of winter season reports. New for winter 2020 is implementation of the National Avalanche Center’s recommendation that resources are best directed towards OSV ranger training and education which will develop stability in the winter snowmobile ranger program. The snowmobile patrol program is now focused on maintaining consistent presence in the Bridgeport Winter Recreation Area. Staff training, review of current practices and policy pertaining to field operations and avalanche awareness will assist in the overall appearance and content of the website and public service information. BACKGROUND The Bridgeport Winter Recreation Area (BWRA) was designated by Congress by the Omnibus Public Land Management Act of 2009. It is the first winter recreation area to be congressionally recognized and designated. The BWRA is a small area of approximately 7,254 acres, encompassing two alpine and subalpine watersheds that provide excellent skiing and sledding terrain and shown in Figure 1. 1 The boundaries of the BWRA follows the watersheds of McKay and Leavitt Creek. MacKay and Sardine Creek watersheds encompass approximately 3,800 acres and define the north and northwest boundaries of the BWRA. The western boundary of the Leavitt Creek watershed is the Sierra Crest. Total acreage of the BWRA is 7,254 acres, similar in size to the Mammoth Lakes Basin. People’s Gate Sonora Pass Bridge SnoTel Leavitt Meadows SnoTel Leavitt Lake SnoTel Figure 2. McKay Creek and Leavitt Creek watersheds and Sno-Tel stations in the BWRA. Three NRCS (Natural Resources Conservation Service) Sno-Tel stations are located in the BWRA (Figure 2), located along an elevation gradient beginning at 9,600 ft near Leavitt Lake to 7,200 ft at Leavitt Meadows. Leavitt Lake Sno-Tel station is located a few hundred yards north and east of Leavitt Lake (Figure 2). The Sonora Pass Bridge station is located at 8,700 ft in the McKay Creek drainage. Leavitt Meadows is located at 7,200 ft. Climate records extend from the 1980’s to the present, offering an unusual opportunity to analyze long term trends in air temperature, and variability in snowpack accumulation patterns and precipitation. The Pacific Crest Trail (PCT) traverses across 2 miles of the BWRA near Sonora Pass. The PCT was designated by the National Trails System Act of 1968 as a non-motorized/non-mechanized trail to provide recreation opportunities for winter and summer recreation. The Omnibus Public Land Management Act directed the Forest Service to establish an appropriate crossing of the PCT for winter motorized users from the BWRA to the adjacent Stanislaus National Forest. Snowmobiles traveling west up the McKay Creek drainage can proceed north to the Sonora Pass Road via the PCT Crossing Area. Most of the terrain within the McKay Creek drainage and the PCT Crossing Area is avalanche terrain. The PCT Crossing traverses below Unnamed Peak (10,900 feet) and above the prominent rock formation in the left center of Figures 3 and 4. The PCT Crossing traverses across shaded, north facing slopes where weak faceted snow and depth hoar are common. Prevailing southwest to west winds transport snow from the west side of the ridge, creating wind deposits on the east facing slopes seen in the photograph. North and east facing slopes above treeline receive little solar radiation during the winter and snowpacks are generally much colder than on southeast to west facing slopes. Weak snow often persists during the entire winter. These slopes also receive significant wind loading from winter storms and avalanches often release naturally during and immediately after winter storms. It is common to find weak faceted snow in shallow snowpacks and can surprise winter recreationists who are used to a forgiving snowpack that allows careless route finding and descents with no consequences. Figure 4 shows the PCT Crossing in low snow conditions on January 31, 2020. The BWRA is open to snowmobiling from December or January until April 15 each year. Permits are required to ride in the BWRA and are easily obtained at the People’s Gate trailhead. In 2017, 1,200 permits were issued, though hand written permits are not obtained by all users, leading to under reporting errors. Online permits will be available for winter 2021: online permitting will make it easier for users to obtain permits and should provide more realistic use figures. Winter use numbers are generally controlled by snow conditions. Heavy snowfall winters such as 2017 and 2019, attract higher numbers of users than drier winters when visitation seems to be better correlation by new snowfall than weekend use. 3 Figure 3. PCT Crossing, January 31, 2020. Photo credit Brent Dull. Snow depth at Leavitt Lk was 41 inches. The avalanche terrain in the PCT Crossing area is easily seen in an average year. Apr 1, 2013. Figure 4. PCT Crossing Area, Apr 1, 2013. Snow depth at Leavitt Lk was 104 inches. Photo credit, Sue Burak 4 SNOW, WEATHER AND AVALANCHES, WINTER 2019-2020 The winter of 2019-2020 had a promising start in late November when an impressive low- pressure system brought low snowlines and significant snow to the Eastern Sierra. With an unusually cold airmass for late November, the 5-day period of wet and cold conditions dropped 44 inches of snow and 8 inches of water equivalent at the Leavitt Lake sensor at 9,600 ft. The Sonora Pass Bridge station picked up 31inches of new snow and 4 inches of water equivalent. Leavitt Meadows picked up 14 inches of new snow and 1.3 inches of water equivalent. This storm was the biggest storm of the season and one of the top ten storms since 2000. Figure 5. Initial phase of deepeing meteorological “bomb” storm. November 26, 2019. The higher elevations of the BWRA picked up 23” of snow in December, about half of the long- term December snowfall average. In January, the prevailing atmospheric pattern shifted toward one that favored occasional weak-to-moderate storms, but no large precipitation events. Leavitt Lake picked up 24” of snow while Leavitt Meadows only received 9” of measurable snowfall. After January 18, only 8 inches of snow fell at Leavitt Lake until March 3. In February, many places throughout the State saw zero precipitation for the first time in over 100 years- a remarkable record for what is typically the wettest months of the year. The dry warm weather was accompanied by continuous east and northwest winds that stripped snow from ridgetops and created icy crusts and thick wind slabs developed throughout the BWRA. Weak faceted snow that formed in December and January remained in the snowpack through April. 5 Figure 6. Persistent northwest winds over the Sierra Crest, February 2020. The average daily temperature in February 2020 was 29.6 F at Leavitt Lk and 33F at Leavitt Meadows. Snow depths taken from snow pits ranged from 30 to 36 inches- shallow compared to the 20-year average February snow depth of 99.4” at Leavitt Lake. Shallow snowpacks develop weak faceted grains in response to higher gradients of temperature from the base of the snow to the surface and can be triggered by skiers, riders and heavy storm snow loading throughout the winter. The season-to-date precipitation deficits gradually increased during February with significant snowmelt occurring on Highway 108 from People’s Gate to the 8,000 ft elevation. Patchy snow and long stretches of asphalt made snowmobile access difficult in February and early March. A side by side was used to drive up to the 8000 ft elevation where sleds were stored. The USFS side-by-side used to transport rangers and gear to snowline is shown in Figure 7. 6 Figure 7. Loading the side by side for a trip into the BWRA. Photo credit, Sue Burak Figure 8 displays snowfall accumulation at Leavitt Lake, Sonora Pass Bridge and Leavitt Meadows from November through mid-April. 2020 Season snowfall, SnoTel stations in the BWRA Leavitt Lake, Sonora Pass Bridge, Leavitt Meadows 120 100 80 60 40 Snowfall, inches Snowfall, 20 0 11/26/2019 12/26/2019 01/26/2020 02/26/2020 03/26/2020 Leavitt Lk Snow Depth, in Sonora Pass Bridge Leavitt Meadows snow depth Figure 8. Snowfall accumulation, winter 2019-2020. Winter snows returned to the BWRA in mid-March with peak accumulation occurring during the second week of April. The plot shows that elevation is a strong predictor of snowfall accumulation (R2= 0.83) in the BWRA. During the prolonged dry spell from mid-January through early March, Leavitt Meadows melted out by March 1 and access to the BWRA required driving on Highway 108 for several miles until snowline was reached at about 8,200 ft. WINTER RETURNS Winter returned to the Eastern Sierra in mid-March, coincident with the COVID-19 pandemic. 30 inches of new snow fell from March 14-15, bringing many riders to the BWRA. Patrollers reported three rider-triggered avalanches and a naturally occurring avalanche in Leavitt Bowl. One avalanche (not shown) was remotely triggered by a rider on flat ground in the Sardine Creek drainage. Remote triggering is unusual in the Eastern Sierra because snowpacks are much deeper than the snowpack of 2020; however, the shallow snowpack promoted persistent weak layers responsible for remote triggering. Figures 9 and 10. Human-triggered avalanches, March 17, 2020. Photo credits, Brent Dull. Figure 10. Human-triggered avalanche, Leavitt Lake area, March 17, 2020.