GREATER LAKE TAHOE AREA, Calif. / Nev. – Hydrologists aren’t holding their breath for a normal snowpack this winter. The Natural Resources Conservation Service (NRCS) says the Lake Tahoe Basin and surrounding regions are experiencing a snow drought in more than one way.

“Too many blue-sky days in January followed by too much rain in early February raises concern about where this winter’s snowpack will end up on April 1,” their Nevada Water Supply Outlook Report says.

April 1 marks the date when the snowpack typically reaches its peak and Feb. 1 represented a discouraging half way point.

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Projections currently show an estimated 30% chance of reaching a normal peak snowpack in the Tahoe basin by early April.

“The bottom line is our mountains have been experiencing two kinds of ‘snow drought’ so far this winter,” the report says.

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One of those is a “dry snow drought” after conditions have trended the wrong direction since New Year’s with below normal winter precipitation in January.

The snowpack at the start of January for the Tahoe basin was above normal levels at around 122%, but the following dry spell resulted in a 62% snowpack on Jan. 31.

Storms since February 1 finally broke the dry pattern and conditions are improving. Early February storms increased the Truckee-Tahoe Basin snowpack to 80% of what the agency considers normal as of Monday, Feb. 10.

However, these storms demonstrate the second type of snow drought, a “warm snow drought,” evidenced by the lack of snow accumulation despite near-normal precipitation. This is a result of warm temperatures and precipitation falling as rain rather than snow.

“Most of the storms we’ve had this winter including the ones in early February haven’t been cold enough,” NCRS says.

Reports reveals water year precipitation percentages are closer to normal than those for the snowpack, especially in Sierra basins.

NCRS monitoring locations (SNOTEL sites) at lower elevations in many basins, including the Tahoe basin, reveal a significantly small snowpack or no snow at all. This is a concern at this halfway point, since SNOTEL sites are installed in locations that typically have reliable snow mid-winter.

A similar pattern was seen as recently at Feb. 1, 2018 when the Tahoe basin snowpack was only 42% of normal despite water year-to-date precipitation at 82%.

If the double snow drought pattern holds, it could result in reduced springtime streamflow. The Sierra snowpack supplies on average about 30% of California’s water needs. Its natural ability to store water is why the Sierra snowpack is typically referred to as California’s “frozen reservoir.”

According to NRCS, if early February storms had been colder, bringing snow rather than rain above 6,000 feet, the snowpack would be approximately 94% of normal, instead of the 80%.

Only a fraction of the precipitation that came by rain was absorbed by the relatively shallow snowpack and incorporated into that frozen reservoir. Snow can absorb some rain, but eventually water starts flowing through it, spiking streamflow across the region.

This mid-winter streamflow can only be captured in basins with sufficient reservoir storage and if reservoir levels are below winter flood control limits. For basins lacking storage, the water will run off down the rivers now and won’t be available to meet demand during spring and summer months.

The NRCS says Lake Tahoe was not full and stored all the rain and runoff, rising six inches last week.  Dave Wathen, Chief Deputy Water Master, equates the six inch rise to filling Boca Reservoir 1.5 times.  

The current state of the snowpack brings with it wildfire risk concerns as thing are likely to melt out earlier and create a longer snow free season where fuels can dry out. The modest snowpack may also spell concern for summer agriculture irrigation demands.

“Hopefully the next two months bring colder storms to fill in the lower elevation snow and increase high elevation snow,” the NRCS report says.

That is exactly what happened by April 1, 2018 after a what was coined a “miracle March,” which bought a late season come-back to all elevations.

A pair of forecasted storms coming Tuesday night are expected to bring weather to the Greater Lake Tahoe region through Friday.