Rain expected Thursday-Monday at Lake Tahoe, now is the time to prepare

SOUTH LAKE TAHOE, Calif. - Emergency managers and weather experts are watching the computer models this week to see how the forecast atmospheric river (AR) is going to materialize, and what it could mean for the Sierra and Lake Tahoe, as well as lower elevations.

The National Weather Service (NWS) in Reno says the storm door blows wide open on Thursday, with models showing the current North Pacific ridge breaking down and allowing a strong upper-level jet to transport subtropical moisture to our region.

The first atmospheric river (AR) arrives Thursday afternoon, bringing what is also known as the Pineapple Express - wind, rain, and upper-elevation snow.

This warmer AR in the higher elevations raises red flags because of the potential for flooding, not only for the Lake Tahoe Basin but also for lower valleys and surrounding foothills around the 5,000-foot level and above, which already have several feet of snow on them.

South Lake Tahoe officials are keeping an eye on the storm, and making preparations for when the AR materializes.

The forecast does not show the same large amounts of precipitation as the historic flooding of 1997 and there is a high probability of snow above 7,000 feet. NWS Reno said there will be some pathways for snowmelt, but unlikely to contribute to significant melting and large runoff. While higher elevations and those with the deepest snowpack will continue to accumulate snow and water equivalent, deep mid-elevations snowpacks are expected to retain most of the projected rain. Some of these areas may begin to develop preferential pathways for melt and start releasing rainfall after
prolonged periods of rain, but are unlikely to contribute significant snowmelt to the runoff.

The deepest snowpack areas will have the capacity to retain the anticipated late-week/weekend rain, and areas of concern are those with less snowpack under 5,000 feet.

Rain combined with strong winds and high humidity will add considerable energy to our record to near-record deep regional snowpack at mid to lower elevations.

South Lake Tahoe Fire Chief Jim Drennan said they have ordered sand for the sandbag locations in the city, and it will be announced when they are ready for the public.

In the meantime, South Tahoe Public Utility District is preparing for the upcoming atmospheric river by refueling generators at field stations, preparing facilities in flood-prone areas, assembling emergency pumps if needed, and increasing staffing levels during the forecasted event.

Extra water can have an effect on roofs as well. If there are ice dams, water can't find a way to flow down off the roof and instead, it is collected.

Drennan said there have been some roof issues in South Lake Tahoe, including some cracking at the Al Tahoe Post Office, and a partial collapse when a beam failed at Sidestreet Boutique. He said there have been other minor breaks, and some eaves and carport issues.

Many may remember the flood of January 1997, where rowboats could be seen on Tahoe Keys Blvd., and many services had to shut down with major travel challenges through the community. In late December 1996, several storms produced a large snowpack in upper elevations, which was 180 percent of normal. Just as in 2023, valleys along the eastern Sierra Nevada front were covered with a large snowpack as well. A subtropical storm system originating in the central Pacific Ocean near the Hawaiian Islands then brought heavy rain to the Sierra Nevada from December 30, 1996, through January 3, 1997. During this period, 27.7 inches of precipitation were recorded at what is now known as Palisades Tahoe, and the National Weather Service recorded 11.6 in. at Tahoe City, Calif. Rain falling below 10,000 ft depleted about 20 percent of the high-altitude snowpack between 7,000 and 10,000 feet and melted about 80 percent of the snowpack below 7,000 ft.

The lake rose over one foot during that storm. This caused major flooding in the Lake Tahoe Basin, mainly along the Upper Truckee River in South Lake Tahoe, and all of that water went down into Reno, causing the historic flood.

Confidence is increasing for another AR arriving as early as Monday, which will bring additional rain, snow, and wind into next week.