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More Floods and Evacuations in California--Plus Wind Gusts Topping 190 MPH

By: Bob Henson and Jeff Masters 6:50 PM GMT on February 21, 2017

The atmospheric river that slammed the central third of California on Monday left its mark in multiple ways, including what could end up as the highest reliably recorded wind gusts for the state (see below). Fortunately, the storm underperformed somewhat when it came to rainfall, much like its older sibling that hit southern California last Friday. Rainfall amounts in Bay Area cities on Monday came in well short of the potential suggested by multiple model runs, although both San Francisco (2.16”) and San Jose (1.87”) managed to set rainfall records for the date.

Even if the rains of the last week haven’t lived up to model-based expectations, they have caused plenty of havoc (see Figures 1 through 3). Power was knocked out to more than 100,000 people in the Los Angeles area on Friday, with several fatalities reported. More than two dozen debris flows had been recorded in nine counties as a result of the Sunday/Monday storm, according to a comprehensive roundup of the last week’s storms from weather.com. One levee breach on Monday night in San Joaquin County was quickly repaired after some 500 people had been ordered to evacuate. Residents of the town of Wilton in southern Sacramento County were under a voluntary evacuation on Monday night, but the Cosumnes River ended up peaking at 12.06 feet, less than an inch above the 12-foot flood stage and more than 3 feet below predictions from earlier Monday.

The storms of the past week have added to multi-month precipitation totals that are getting steadily more impressive. Many points across central and northern California have already recorded more precipitation than they get on average in an entire October-to-September water year. As of 4:00 pm PST Monday, San Francisco International Airport had racked up 15.70” of rain since January 1. Phil Klotzbach (Colorado State University) noted that this is the fourth highest January-February total on record for the airport, where data collection began in 1945. By midnight Monday night, this year’s Jan-Feb total had climbed to 16.38”. Meanwhile, downtown San Francisco is already at its seventh wettest Jan-Feb in records going back to 1855, with 17.63” as of Wednesday morning. The station is likely to vault to at least fourth place by the time the month is done, but going any further will be a challenge, based on stats tweeted by Klotzbach. During the catastrophic Jan-Feb of 1862, downtown San Francisco recorded 31.89”.

Figure 1. For the first time since the floods of 1997, the Don Pedro Reservoir spillway gates were opened on Feb. 20, 2017, in Tuolumne County, California. The Stanislaus Consolidated Fire Protection District told KCRA.com that up to 20,000 cubic feet per second of water was being discharged as of 3 pm PST Monday. Water flowing from the reservoir will enter the Tuolumne River, where authorities are advising some residents to evacuate and seek higher ground. The spillway will be open for at least four days. Image credit: Twitter/@TuolumneSheriff

Figure 2. For the first time in over a decade, water flows into the iconic 72-foot diameter Glory Hole spillway at Monticello Dam on Monday, Feb. 20, 2017, in Lake Berryessa, California. The unique spillway operates similarly to a bathtub drain. Lake Berryessa is the largest lake in Napa County, California, and is formed by the Monticello Dam, which provides water and hydroelectricity to the North Bay region of the San Francisco Bay Area. Image credit: AP Photo/Eric Risberg. See also the video embedded at bottom.

Figure 3. Officials look over the scene where a San Bernardino County Fire Department fire engine fell on February 17, 2017, from southbound Interstate 15, where part of the freeway collapsed due to heavy rain at Cajon Pass, California, late last week. Image credit: David Pardo/The Daily Press via AP.

A truly wild night in the high Sierra
Two high-elevation weather stations at California’s Squaw Valley resort experienced incredible winds on Monday night as the core of the jet stream associated with the atmospheric river came through, together with localized wind acceleration from a low-level jet encountering the Sierra crest. (Thanks to WU member BayFog for pointing out the multiscale interactions.] Between 10:45 pm and 11:00 pm PST, the Siberia (Sierra Crest)-Squaw station, or SIBSV--located at an elevation of 8700 feet near the top of Squaw Peak--recorded a peak wind gust of 193 mph, with sustained winds reported at 123 mph. During the same interval, only about two miles to the southeast, the Summit (Ward Mt)-Alpine station, or SUMAM--perched atop Mt. Ward at 8643 feet--recorded a gust to 199 mph, with sustained winds of 148 mph.

Extreme gusts over 150 mph are no stranger to the high Sierra. In a 2011 blog post, WU weather historian Christopher Burt referred to an undated state record gust of 176 mph from the Mt. Ward station. Just last month, on January 8, the same station notched a 174-mph gust. (If it’s any comfort, the atmosphere at this height is about 25% thinner than at sea level, so the wind exerts less force.)

Figure 4. Preliminary data from the summit of Ward Mountain in California’s Squaw Valley ski resort show a gust to 199 mph (highest green dot). The gust occurred between 10:45 and 11:00 pm PST on Monday, February 20, 2017. Image credit: MesoWest/University of Utah via National Weather Service.

The closeness of Monday night’s amazing gusts in both time and space, as part of a multi-hour ramp-up in wind speeds, is a strong clue that the data are likely valid. Also lending credence is the location of these two stations: near ridgetops in a highly wind-prone area. “Everything would suggest that it’s pretty legit,” said John Horel (University of Utah), an expert in Western weather and climate and coordinator of the MesoWest observation network. I also got in touch with Sam Kieckhefer, the public relations coordinator for Squaw Valley/Alpine Meadows. “As far as what people have seen in recent history, it’s definitely the highest [wind gust] that has been noted,” Kieckhefer said of the 199-mph gust. The two Squaw Valley stations were installed in the 1980s, with the Siberia station at close to standard height (10 meters, or about 33 feet); information on the height of the other station wasn't immediately available. Gusts at these stations are reported every second (i.e., instantaneously), according to Western Weather Group, which works with Squaw Valley on data collection. The 1-second tempo is typical of Remote Automatic Weather Stations (RAWS). It would tend to yield slightly higher values than the 5-second gusts used by stations in the Automated Surface Observing System (ASOS). Still, it appears that the 199-mph gust could be a valid contender for the highest wind gust in California weather annals and one of the strongest gusts recorded near ground level in U.S. history.

Bob Henson and Jeff Masters

Video 1. Drone footage of the iconic 72-foot diameter Glory Hole spillway at Monticello Dam on Monday, Feb. 20, 2017, in Lake Berryessa, California.

Flood High Wind

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