Weather Watch

It’s been a record year for rainfall and snowpack — but we’re not done just yet

Water races down Nacimiento Lake's main spillway

The Monterey County Water Resources Agency was releasing water from Lake Nacimiento’s main spillway as part of its effort to maintain flood control space in the reservoir. The lake was at 87 percent capacity on Monday, February 27, 2017.
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The Monterey County Water Resources Agency was releasing water from Lake Nacimiento’s main spillway as part of its effort to maintain flood control space in the reservoir. The lake was at 87 percent capacity on Monday, February 27, 2017.

The California Department of Water Resource’s index of eight separate rain/snow gauges across the northern Sierra Nevada recorded a composite average of 90 inches of precipitation this water year — also called hydrological year, which runs from Oct. 1 through Sept. 30.

That broke the previous record of 89 inches set in 1982-83. Data from this set of gauges began being recorded in 1920. One of the gauges in this index — the Blue Canyon weather station on the American River east of Grass Valley — has recorded 126 inches of precipitation. Typically, that station records about 63 inches for the entire year. With more wet and snowy weather predicted in this beautiful part of the state Sunday into Tuesday, these record numbers will continue to grow.

Across the entire Sierra Nevada, various electronic sensors indicate that the water content in California’s vast, icy reservoir is at 178 percent of historical averages as of Friday. If the weather models verify, the central Sierra Nevada’s water content, which is currently at 181 percent, could break the record of 188 percent set in 1982-83.

That’s quite a change from 2014-15, when water content dropped to 2 percent in April.

With above-average snowfall that fell during the first half of April, the snowpack continues to replenish itself in spite of some snowmelt. Continuous rewhitening of the snowpack has increased albedo (reflectivity) and will help delay the spring snowmelt, pushing the primary melt period later into the season, which will result in higher and colder creek and river flows than we usually see.

As a side note, if you happen to venture near these waterways, please take precautions. Sudden immersion in cold water can stimulate the “gasp reflex,” causing an involuntary inhalation of air or water. It can even trigger cardiac arrest, temporary paralysis, hypothermia and drowning. When faced with swift water, even the strongest swimmers can be easily overwhelmed. Cold water entering the ear canal can cause vertigo and disorientation. This may confuse swimmers, causing them to venture deeper into the water.

So what happened this season?

This year — like the weak La Niñas of the 1964, 1994 and 2004 rain seasons — saw a blocking high in the Gulf of Alaska/Aleutian Islands split the jet stream into the polar to the north and the Pacific jet stream to the south like a sand bar in the middle of a river. This condition — along with a persistent trough of low pressure off the West Coast — combined with an area of high pressure over the Southwest to cause the Pacific jet stream to track over California and steered a significant number of low-pressure systems and surges of atmospheric rivers from the Pacific Ocean toward the state.

This condition produced huge amounts of precipitation because of orthographic enhancement in the Golden State’s majestic mountain ranges.

Although we have seen a few strong storms along the Central Coast, this year has been characterized by a nearly endless stream of numerous modest weather systems. That resulted in above-normal rainfall in most locations, especially in the coastal mountain ranges.

For example, Debby Mix of the Circle 3 Ranch, which is located in the San Simeon Watershed between Vulture Rock and Rocky Butte, recorded more than 100 inches of rain. Cal Poly (home of climatology for San Luis Obispo) has recorded more than 32 inches, or 143 percent of normal, for the entire rain season, which runs from July 1 to June 30. Paso Robles Airport has seen 14 inches of rain. Generally, for the whole rain season, they receive 12.5 inches.

The Santa Maria Airport has recorded more than 17 inches. Typically, 13 inches of rain falls at that location.

A couple of more modest cold fronts are expected to pass through the Central Coast on Sunday night into Tuesday morning, with rainfall totals reaching between a quarter and a half an inch. That may be just enough rain to keep in the mountains of the Central Coast emerald green for a few more weeks before turning to hues of golden brown.

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Celebrate Earth Day on Saturday by joining PG&E employees for a work project at Montaña de Oro State Park. The event is one of many service projects sponsored by PG&E and the California State Parks Foundation.

Be sure to dress for outdoor work with long pants, a long-sleeved shirt, sturdy shoes, hat, gloves and sunscreen.

Snacks and lunch will be provided. Bring a refillable water bottle. Rangers will provide tools and supervision. Please register at the California State Parks website at calparks.org/help/earth-day/.

John Lindsey’s column is special to The Tribune. He is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter: @PGE_John.

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