By BRYAN ALLEGRETTO and ZOE NAJIM  |  Moonshine Ink
Snow is the glue that holds Tahoe together through the winter, and here, local weather experts Bryan Allegretto and Zoe Najim channel their inner Charles Dickens in breaking down storms of Tahoe’s past, present, and future. ~ Ally Gravina

That Dam Discharge

PAST: Discharge out of the lake didn’t make it over a drip from January of 2015 all the way to July of 2016, when the basin finally received precipitation from convective activity creating some short-lived flow. The highest peak rate of discharge at the Tahoe City dam was in 1997 when it briefly reached more than 2,500 cubic feet per second. Through most of the winters since 1997, peak discharge rates were less than 500 cubic feet per second.

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PRESENT: During the winter of 2017 the discharge rate at the Tahoe City Dam, at its peak, briefly reached a little more than 2,100 cubic feet per second!

FUTURE: The water discharge rate today is very low, due to a pretty dry autumn. With near to below average precipitation forecast for this winter, we may see an average flow but are not expecting any records again.


Snowfall

PAST: The previous highest snowfall amount for January was in 1973, when 159 inches fell at the top of Donner Summit — in fact, 238 inches is the highest monthly total of any month since 1970. Last January’s snowfall totaled more than the year totals for the winters of 2014/15 [which had a year total of 130 inches], 2013/14 [with a year total of 194 inches], or 2012/13 [with a total of 215 inches]. Data taken at Donner Summit.

PRESENT: 2017 had the highest snowfall amount for the month of January of any year since 1970, when records for monthly snowfall amounts began, at 238 inches at the top of Donner Summit.

FUTURE: Over the past 10 years, on average, January has had less snowfall than December, February, or March. In recent La Niña seasons we have seen both above and below average snowfall in January, so it could tilt either way.


The Big Years

PAST: The biggest season on record was 1951/52 with a total of 800 inches! The next highest snowfall amount was in 1982/83 with 671 inches at Donner Summit. After that was 2010/11 with 643 inches followed by last winter. Average snowfall is considered to be 409 inches at Donner Summit, however, very few years are average. In fact, only 11 winters were at or near average since 1950, so average isnot really normal in this area!

PRESENT: The total for the season of 2016/17 was 573 inches at Donner Summit. It was later termed #snowmaggedon.

FUTURE: Almost every big year of snowfall on record was followed by a drop to less than average snowfall amounts. Exceptions were 1981/82 which was followed by an even bigger year. 1997/98 which was followed by a good year even though it was not as big as the prior year, and 2009/2010 which was also followed by an even more impressive year. As for the Southern Oscillation (El Niño/La Niña) we are in a neutral phase with La Niña favored to develop for this winter. According to NOAA’s long range forecast (3 months) we will have warmer conditions than normal and average precipitation during October, November and December. Our forecast for this season is 85 to 95 percent of average snowfall based on previous winters with similar atmospheric conditions as forecast for this season. That wouldbring 348 to 389 inches to Donner Summit.


Hydroelectricity

PAST: The generation of hydroelectricity was at 20,937 megawatt hours year-to-date in August 2016 in California.

PRESENT: 33,929 thousand megawatt hours were produced year-to-date by August of 2017, a jump of 62.1 percent.

FUTURE: With the start we have had this November and wet storms we should be off to a good start with megawatt hours again this season. But with a dry forecast the first half of December and a slightly below average precipitation year forecast, we may fall back closer to 2016 levels.

 

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