Sunday, April 26, 2015

April (Snow?) Showers

Let's take a quick look back at the storm that unfolded across the Sierra and western Nevada on Friday night into early Saturday morning. We were discussing this storm on the midnight shift, and we would rank it as one of the top 5 "winter" storms this season. Too bad it is a few months too late to really assist with the snow pack, which is what we desperately need to help alleviate the drought pains. I guess we should just be appreciative of what rain and snow that we got.

Snow totals were pretty decent for this time of year. We actually had multiple reports of around 10 inches in the Tahoe basin and a few back country snow sensors reported around 12 inches!

Chain controls were across most of the Sierra passes from early Saturday morning until the showers lessened and the sun allowed the roads to begin warming up. We were a bit surprised to hear the road to Bodie National Park and Monitor Pass (Highway 89) actually remained open during the event! The high sun angle really limits the impacts to roads this time of year, so that was a benefit to travelers across those Sierra passes.

What can we expect now that this storm has exited the region? We are looking at a decent warming trend for early this week. Afternoon highs could get within a few degrees of the record highs on Tuesday. So all of you weekend warriors will finally have some prime weather for running, biking, unicycling, etc. So enjoy!

Monday, April 13, 2015

The Drought

The Drought, Year 4 - A Sierra Perspective

Wow, I would never have expected the snowpack in 2014/15 to be a fraction of what we saw during the winter of 2013/14. As a Meteorologist it is interesting to see the full range of winters the Sierra Nevada has to offer, with memories not so distant of the record setting deep snowpack of 2010/11 that immediately preceded the current drought. However, as a human, who lives in the Sierra and moved here to ski its deep snowpack, it’s downright depressing.

Left image is the Sierra snowpack on March 27th 2010. Right image is the Sierra snowpack on March 29th 2015

Where do we stand now....

As of the beginning of April, this has been the least snowy year on record at Donner Summit since the Central Sierra Snow Laboratory was established in 1946. For the first time on record the snowpack melted down to zero in March! The previous lowest snowpack measurement in March was 14 inches, and that was last year. March 27th is the average date of the maximum seasonal snowpack at the snow lab where the snow on the ground averages 10 feet.

Height in cm of the total snowpack on the ground during the 7 least snowy years at the UC Berkeley Central Sierra Snow Lab.
Detailed daily snow observations at the snow lab go back to 1946. 

There are many different ways to look at precipitation and how the current drought compares to the past. A common measure we use is a combination of sites called the Northern Sierra 8 station index. By this measure, none of the last 4 years in the northern Sierra is even close to setting any records. However, looking a little further south, the Southern Sierra 5 station index is very close to record dryness this year and has been generally drier then the northern Sierra over the last 4 years.

In combination though, the four years of below normal precipitation is adding up. Looking at statewide precipitation totaled over 4 years ending in March 2015, the last four years rank as the #1 driest for California and 10th driest for Nevada in the 121 year record starting in 1895. 

On the Nevada side, the water running in the Truckee River will be without its biggest reservoir this summer since the level of Lake Tahoe has dropped below its natural rim. While this is not without precedent, this along with the soon to be snow-free peaks will be a visual reminder of the ongoing drought. This week Governor Sandoval signed an executive order establishing the Nevada Drought Forum to “study and analyze the state water use and potential areas for water saving”. Sandoval didn't go as far as mandating water cuts as Governor Brown has in California. In a recent article Sandoval said, “We're not in the same position as California. It isn't an emergency.” Sandoval also noted, “We are and have always been the driest state in the nation. Drought affects all Nevadans.”

What’s different this time?

This time is different from past droughts though, for multiple reasons. First the population of the southwest U.S. has significantly increased since some of the most memorable droughts in the 70’s and during the dust bowl of the 30’s. California has also been the #1 food and agricultural producing state for the last 50 years. In Nevada, using data from 2010, the direct and indirect economic impact of Nevada’s agriculture is estimated at over 5 billion dollars. 

Probably the most important difference this time has been temperature, and thus, the snow level. Across nearly all of California and Nevada, temperatures this past winter have been the warmest on record, since 1895.

This time much of the precipitation that normally falls as snow came in the form of rain. The left side of this graphic from April 1st, approximately the date of maximum snowpack, shows that the central Sierra received around 50% of average precipitation. The right hand side shows the total snow water equivalent of the snowpack, which ranges from 20% down to an abysmal 2% of average in the Tahoe Basin. Looking further north into the Cascade Range of Oregon and Washington you can see the dramatic difference between the seasonal precipitation and the seasonal snowpack. Most of the Cascades received near normal precipitation with record breaking low snowpack. Across the west from California to Washington, the few big atmospheric river storms we did receive were warm with high snow levels, resulting in this big difference between total preciptiation and snowpack.

USDA/NRCS National Water and Climate Center Portland, Oregon

As I write this the skies are clearing from a late season storm here in the Sierra where around foot of snow fell and nearly doubled our snowpack. Unfortunately it was from an abysmal 2%, to a still record-crushingly low 4%.

Well, that’s our summary of the current drought from the Sierra perspective. Here’s hoping for an average Sierra winter in 2016.