Yet another in a long line of winter storms will move through the region on Saturday, adding several inches of snow to the mountains, but only likely to produce scattered rain or snow in the western Nevada valleys due to shadowing. The main precipitation band will move through fairly quickly Saturday leaving a mostly dry Sunday before the next weak storm tries to move through on Monday. The long-term outlook seems to keep us in a fairly active pattern of weak to moderate storms coming through on an every-other day or so frequency.
Yesterday, Jim wondered if a typical El Niño would increase our chances of flooding. While flooding might seem logical, let me dispel a couple of misconceptions about El Niño. While flooding can be an issue with El Niño patterns in southern California, El Niños are not any more likely to cause flooding here in northern Nevada than non El Niño years. The biggest floods we’ve had here in the Reno area weren’t associated with El Niño, but rather atmospheric rivers, which are not any more prevalent in El Niños (and in fact may occur more often in La Niñas.)
Some have written me asking if it will really do us any good from a water standpoint, because of a concern that El Niños have so much higher snow levels, and wouldn’t that just reduce the amount of snow, especially in the lower elevations? The storms we are seeing this week do fit the “El Niño signature,” although even that is a pretty loosely defined criterion. And an El Niño doesn’t necessarily demand a high snow level, although on average they do tend to be a bit higher. But there is a lot of buffer to snow levels, and even if the slow levels are a bit higher, the additional moisture more than makes up for it. Of course lately our snow levels have been pretty low with most of the valley precipitation in the form of snow.
Right now, we are already well ahead of a “normal” snowpack for this time of year, with our 4 basins ranging between 110% (Truckee River Basin) and 140% (Tahoe Basin) of average for this time of year, and that doesn’t take into account what they got yesterday. There really hasn’t been such a thing as bad precipitation lately.