climate, weather

Sierra Nevada snowpack increases dramatically; drought conditions wane (H. Michael Mogil, CCM, CBM, NWA-DS*)

When the computer models started to forecast incredible precipitation amounts for the Sierra Nevada Mountains of California and Nevada earlier this month, I thought the numbers were somewhat exuberant. After all, California has been in the throes of an extensive and hard-hitting drought for several years. However, this storm event (and the one on the western horizon) are welcome news for a state that lives in drought.

According to the National Weather Service (NWS) Forecast Office in Reno, the early January stormy period (Jan. 2 – 13, 2017) transformed the Sierra snowpack from a sub-average value to one that is pushing 200 percent of seasonal average (Fig. 1). This snowpack provides California’s dry season river runoff, water for agricultural and human uses and other aspects of California’s existence. The snowfall is also helping to boost ski resort business (at least, once folks can get to the ski areas).

It’s easy to see the impact of this precipitation on the California drought (Fig. 2). Note that the data cutoff for Drought Monitor maps is each Tuesday at 7:00 a.m. E.S.T., even though the maps are published each Thursday at 8:30 a.m. E.S.T. Hence, next week’s maps will likely show a further reduction in drought coverage across California.

Observations indicate that the high Sierra received between 9 and 15 feet of snow since the start of 2017. In the Tahoe Basin, within the “rain shadow”** of the Sierras, 2 to 5 feet of snow fell, except for the west shore of Lake Tahoe which received

between 6 and 8 feet of snow. For the Virginia Range (located just east of Lake Tahoe), reports indicated over 2 feet of snow had fallen, while along Highway 395 between Bridgeport and Lee Vining (on the east side of Yosemite National Park) between 1 and 4 feet of snow was reported.

Forecasters see a brief break in the stormy weather pattern through early next week. Then, more valley rains and mountain snows are on the menu (Fig. 3).

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** The “rain shadow” lies downwind from a mountain range. It typically receives lesser precipitation amounts because upslope winds on one side of the mountain receives the heaviest precipitation, while downslope winds on the rain shadow side receive less precipitation. For the Sierra’s, west winds provide the upslope across much of California; as the winds cross over the mountains, lighter precipitation occurs across western Nevada and the Lake Tahoe Basin.

© 2017 H. Michael Mogil

Originally posted 1/14/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.