El Nino, the California drought and Sierra Nevada Snow

Yesterday Anthony Watts wrote one of his rare articles about the drought in his home state of California (archived here). His headline read: "Drought buster? Up to 10 feet of snow this week for California’s Sierra Nevada". Under the headline he wrote (my emphasis):

Here is some good news for drought-stricken California; the latest forecast model output from WeatherBell suggests that the Sierra Nevada snow-pack will get a fresh dump of up to 10 feet of snow. 

He posted the chart below, with a scale up to 48 inches from the look of it, not 120 inches (though the scale doesn't indicate units). Up the top it states "Maximum 147.6 in". (Click to enlarge it).

Source: WUWT

His prediction of ten feet of snow this week struck me as rather a lot in just a few days. Not knowing how quickly snow can build up in the region I did some research. "This should hit the headlines", I thought to myself. However the only news I could find on the Sierra Nevada snowpack were about how up to "2 feet of fresh snow are expected to fall this week in the Sierra Nevada's highest points" (Associated Press in the Sacramento Bee - 3 January 2015). That's eight feet short of Anthony's ten feet prediction.

Accuweather is perhaps a bit more optimistic, forecasting snow "measured in feet" in the Sierra Nevada, and one to three feet of snow in southern California mountains:

Snowfall will be measured in feet across the Sierra Nevada. Snow this week could cause travel problems near Donner Pass. ...

...According to AccuWeather Meteorologist Dave Samuhel, "The storms during the second half of the week have the potential to unload 1-3 feet of snow on the mountains and ski resorts of Southern California."

Wunderground forecasts one to two feet of snow through to Friday this week:

Through Friday, 1 to 2 feet of snow seems a good bet in much of the Sierra, with over 2 feet in the highest elevations. Heavy snow in excess of 6 inches is possible across some of the higher elevations of northern Arizona Mogollon Rim, the canyonlands of southern Utah, higher elevations of southern Nevada, southwest Colorado and western New Mexico.

Below is the forecast map, showing more than 24 inches in parts:

Source: Weather Underground

We'll have to wait and see just how much snow will fall, and where. Anthony might be correct, or he might not. I could not find another report forecasting ten feet of snow in the Sierra Nevada. The best I could find were reports of rain over the next few days, enough to cause some minor flooding and landslides, but no deluges, and probably quite a bit of snow in the mountains. Maybe a few feet in places over coming days, but outside of WUWT (and its copy and pasters), I could find no mention of a dump of ten feet of snow.

Update - see conclusion below.

Snow reports for Sierra Nevada Resorts

Anyway, I'll keep an eye on the reports of the ski resorts in the Sierra Nevada. I took the first snapshot about 15 hours after Anthony's article first appeared. Note the time of the last update alongside each resort's report. I'll add further reports over the week as they appear.

• 5 Jan 2016 01:59:16 UTC - no snow in the past 24 hours, except for Mountain High which reported an inch of snow
• 5 Jan 2016 18:17:28 UTC - a few inches of snow has now fallen at the various resorts listed - the most being 6" in the last 24 hours
• 6 Jan 2016 01:57:38 UTC - there is snow reported at quite a few resorts in the last 24 hours (seven had a zero report). The highest in 24 hours was at Badger Park, with 12". The highest 72 hours was Mammoth Mountain with 15".
• 7 Jan 2016 00:49:43 UTC - more snow has fallen at most resorts over the last 24 hours. For example, at "upper" Mammoth Mountain, the base is now 10 inches deeper than it was in the first entry above.
• 7 Jan 2016 12:38:33 UTC - now it's showing no snow in the past 24 hours. It might just need updating, don't know. The most in the past 72 hours was 30" at Badger Pass.
• 8 Jan 2016 02:47:00 UTC - It's been snowing again. The biggest fall in the last 24 hours was 23" at Ski China Peak (39" in 72 hours), where the upper base has increased by 18" from 52" to 70". The highest in 72 hours was Badger Pass at 48" (four feet), which is also the base depth on it's upper slopes. Mammoth Mountain is now recording a base depth in the upper slopes of 115", and increase of 30" from the first day.
• 8 Jan 2016 18:32:33 UTC - nothing to speak of in the past 24 hours, except for Badger Pass (24") and it also has the most again in the past 72 hours, now five feet of snow (60").
• 12 Jan 2016 06:49:33 UTC - hardly anything reported for the past 72 hours.

Conclusion: Anthony got it very wrong. Ten feet of snow is 120". Going by the snow reports there was nowhere near a total fall of 120" of snow at any of the resorts in the past week.  Some got a lot - maybe two to four feet. Accuweather and WeatherUnderground were much closer in its forecast. Most of the resorts now have good to excellent cover now - so enjoy the skiiing :)

Sou 12 January 2016

Biggest snowfall in the USA: Incidentally, the most snow in a single storm in the USA is reported as falling in 1959 in the the old Mount Shasta Ski Bowl in northern California, where a total of 15.75 feet (189 inches) of snow was measured from February 13-19.

Will it be enough to break the drought?

In regard to Anthony's hope for breaking the drought, well it's too soon to tell but the signs are hopeful that it will make a dent in it for parts of California at least. Anthony wrote, before copying and pasting a random segment of a press release from the California Department of Water Resources:

The Sierra snow-pack has already been reported as above normal (at 136 percent of normal) in the most recent snow survey conducted by the California Department of Water Resources.

Anthony left out important information. His 136 per cent of normal was only for one site. The press release he linked to was a tad more reserved stating that overall there was 105 per cent of water equivalent in the statewide snowpack as at 30 December:

More telling than a survey at a single location, however, are DWR’s electronic readings today from 99 stations scattered throughout the Sierra Nevada. Measurements indicate the water content of the northern Sierra snowpack is 11 inches, 108 percent of the multi-decade average for the date. The central and southern Sierra readings were 12.1 inches (116 percent of average) and 7 inches (86 percent) respectively. Statewide, the snowpack held 10.2 inches of water equivalent, or 105 percent of the December 30 average.

A lot of water will be required for the state to get over the drought, and it's hoped that El Niño will bring it. There are no guarantees. The report Anthony linked to, from the California Department of Water Resources states that the water storages are very low, with Lake Oroville, for example, holding considerably less water than it did last year:

Despite snowpack readings that are higher than last year, the major water reservoirs are storing far less water this year than their late-December historical averages. Lake Oroville in Butte County, the State Water Project’s (SWP) principal reservoir, now holds 1 million acre feet (MAF), 29 percent of its 3.5 million acre-foot capacity and 47 percent of its historical average on December 30. One year ago today, Oroville’s numbers were 1.3 MAF, which was 62 percent of its December 30 average.

The snow needs to melt before it fills up the water storages, and some of the melt will soak into the parched ground before filling up the reservoirs. From the San Francisco Sacramento Bee on 30 December, after the above report was released

The state decides whether a drought has officially ended based on factors that would ensure California can weather the hot spring, summer and fall months, when little rain falls in much of the state.

Thomas said at least one of three things would need to happen for the drought to be over: statewide reservoir storage would need to be at 90 percent of average levels; runoff forecasts for the state’s water year, which runs from October to September, would need to be 110 percent of average; or reservoirs on the four major rivers in the Sacramento River basin would have to reach flood control stage.

“Any of those things gives us a pretty good signal that we can say, optimistically, that we’re nearing the end of the drought and perhaps have,” Thomas said.

This is the drought report for California to the 29 December, when there was no part of the state not in drought - click to enlarge:

California's rains come from atmospheric rivers, the risk they are blocked is increasing

Last July a paper by Andrey K. Savtchenko, George Huffman and Bruce Vollmer (all of NASA) was published in the Journal of Geophysical Research. They reported some interesting findings about precipitation patterns in California, based on data from satellite and reanalysis (Tropical Rainfall Measuring Mission, TRMM, 1998–2014 and Modern-Era Retrospective Analysis for Research and Applications, MERRA, 1979–2015):

• The 1986–1994 decline of precipitation was similar to the current one that started in 2011. In terms of accumulated deficits of precipitation, that episode was no less severe than the current one. However this recent episode was more severe in another respect, having doubled occurrence of very weak precipitation compared to the 1986-1994 period.
• While El Niño is frequently cited as the natural forcing expected to bring a relief from drought, our assessment is that ENSO has been driving at best only 6% of precipitation variability in California in the past three decades.

The authors described the period leading up to the 1997/98 El Nino, and compared it to the current drought situation:

Starting in 1986, the climate in California shifted to a pattern of persistent deficits that gradually deepened to levels not seen in the past 35 years (Figure 3). In the winter of 1994–1995 the precipitation started to rebound, with a particularly strong recovery in the winter of the strong 1997–1998 El Niño. The current decline of precipitation, an episode that Figure 3 implies started in 2011, shows up as very similar to the 1986–1994 episode.

Below is Figure 3 from the paper, I've annotated it with the start of the decline and arrows to show the rate of decline (which was faster in the recent period than in the earlier period):

The authors find that the accumulated deficit was about a year's worth of rain. In other words, to make up the deficit, California would need twice the average year's rainfall. They wrote:

Technically, to eliminate the previous 2 year (2012–2014) deficit by the end of the 2014–2015 rain season (that is, August 2015), TRMM estimates that California should receive the expected for the season and the accumulated deficit to a total of 847 mm. The available MERRA data for 2014–2015 rain season, however, showed that the onset of this season was similar to the 2012–2013, Figure 4. The precipitation initially picked up well in November, to only level in subsequent months. Our late estimates (not shown), using less accurate real-time TRMM and GEOS-5 forecast, reveal that California received only about 330 mm, from August 2014 to the end of June 2015, adding another 150–180 mm to the deficit. This means that the state is currently missing at least 1 year amounts of precipitation.

The finding that "only 5–6% of precipitation variability in California is driven by ENSO" means that "while El Niño is more likely to enhance precipitation in California, the adverse effect is also probable, like during the weak warm ENSO that persisted in 1990–1995". In other words, if this El Niño doesn't deliver an over-abundance of rain as hoped for, then California will not recover from the drought in the immediate future. In their summary they restate the amount of rainfall deficit around the time of publication (after the 2015 winter/wet season). It needs an additional one full year of precipitation, or double the average annual precipitation, to get back to average:

We assess the deficit for the 2014–2015 season at 170 mm/m2 and thus the deficits from all three seasons, August 2012–2015, add up to 1 year of expected precipitation. Even though 2012 is frequently cited as the beginning of the episode, TRMM and MERRA data show the decline of precipitation actually started in 2011. Thus, we are confident California is currently missing at least one full season of precipitation.

They added that population and land use pressures are growing which, combined with an increase in atmospheric blocking patterns, doesn't bode well for California:

A number of research groups conclude that the frequency of the blocking atmospheric patterns driving these episodes has increased since the preindustrial age [Herring et al., 2014]. Anthropogenic attributions left aside, every next dry episode is still very likely to be felt more strongly. Assuming perfect climate, precipitation amounts in California are finite and constrained at about 500 mm/m2/yr, whereas the population and land use are growing and thus are likely to exert more significant stresses on water resources demands than climate warming [Hanak and Lund, 2008].

As I understand it, the authors are saying that because Californian rains mostly arrive from atmospheric rivers (bringing huge downpours and snowfalls), the risk is that they will be blocked (atmospheric blocking patterns) and not reach California. This is quite different from regions that get more steady rainfall, perhaps spread out over a wet season. California is dependent on episodes of intensive rainfall. They wrote:

TRMM data, being at finer spatial resolution, assess the risks of losing the most intensive 5% of storms to have been at almost 90% for the 2011 episode. ...MERRA data imply that the loss of the most intensive 5% of storms has been more likely in the current episode. The dramatic difference in the current episode is the doubled occurrence of very weak precipitation (the weakest 5%) as compared to the typical periods. In these terms, the current episode is more severe than the 1986–1994 decline of precipitation.

The Megadroughts

Anthony added a chart to the bottom of his article, writing "It is instructive to keep in mind that decades-to-century scale droughts have been part of California’s landscape".  It's true that California has had big droughts in the past. I've written about that before - which you can read here. There are numerous ironies in his recalling that chart (from a newspaper, not from a paper; about a tree-ring study; about the fact that it only goes to 2003 and doesn't include the recent drought; the fact that it's not just about California; and more.)

References and further reading

Savtchenko, A. K., G. Huffman, and B. Vollmer (2015), Assessment of precipitation anomalies in California using TRMM and MERRA data, J. Geophys. Res. Atmos., 120, 8206–8215, doi:10.1002/2015JD023573.

California 'rain debt' equal to average full year of precipitation - press release at Science Daily about the above paper.

Measuring Snow And Amusing Your Neighbors - an article by Bruce Mason on how snow depth is measured, in Teton Valley News.

From the HotWhopper archives

• Anthony Watts claims a scientist ignored his own work on US droughts - August 2015
• Stop the presses! Anthony Watts has mentioned the Californian drought - then does a Tisdale - July 2015
• The Californian drought is the worst in 1,200 years - December 2014 
• Finally - another WUWT article on the drought in California - November 2014
• Human influence on the Californian drought - October 2014
• Finally, if a "bit too late" - Anthony Watts talks about the drought in California - January 2014