Tag Archives: weather

SoCal Rain Update: Keep it Coming

After 5 long years of drought, a series of powerful storms in January and February 2017 finally brought heavy rain and snow to California. Let’s take another look at where we stand in Los Angeles, and at water supplies around the state. As always, remember that in California we measure precipitation from October through the following September; this period is called the water year.

Currently, downtown LA is at 18.50” of rain for the water year. This is about 3.5” greater than the yearly average, and well past any of the drought years.

laraintable-20170301laraingraph-20170301

February 2017 finally brought a storm that put the Central Coast in the bullseye, and the effect on Lake Cachuma, the largest reservoir for Santa Barbara County, was incredible. So far this winter, Lake Cachuma is up from 7% full to 42% full, and on one day in February gained nearly 30,000 acre-feet of storage. (One acre-foot is enough water to cover an acre of land with one foot of water, about what two average households in CA use in a year).

cachuma-20170301

Precipitation indexes for the Sierra Nevada show it’s been a very wet year throughout the range. The north Sierra, corresponding to the Sacramento River drainage, has had 76.3”, already well above the water year average of 50.0”, and with all-time records within reach.

nsierra-20170301

The central Sierra, corresponding to the San Joaquin River drainage, is also already well above the water year average, with 60.4” to 40.8”. It too is on pace to chase some of the wettest years on record.

sanjoaquin-20170301

The south Sierra, corresponding to the Tulare Basin (Kings, Kaweah, Tule, & Kern Rivers), is now well above the water year average, with 40.9” to 29.3”.

tulare-20170301

Let’s look over to the other side of California, the east Sierra, corresponding to the Owens Valley. Snow water content has not only already doubled the April 1 average (50.4” to about 24”), it’s already tied the wettest year on record. This is where the water in the LA Aqueduct comes from, so it’s good news for city water supplies, as we’ll have to buy less water from the State Water Project and Colorado River Aqueduct.

esierra-20170301

The juxtaposition of such a wet year following the worst drought in the state’s history has highlighted that California, especially southern California, is the land of extremes. Annual precipitation in SoCal is almost comically variable, with the wettest year having over 10 times as much rain as the driest year.

cavariability

Variability is expressed using coefficient of variation (standard deviation divided by mean). LA’s coefficient of variation is 0.48.

To demystify the variability of SoCal rainfall, I thought it might be interesting to do a comparison between Los Angeles and Portland, widely considered to be a pretty rainy place. Here’s the average rainfall for each city by month.

lax-pdxavg

Portland gets about 36” of rain every year to LA’s 15”, though surprisingly enough LA is, on average, wetter than Portland in the month of February. However, when we look at daily rainfall records, a striking pattern emerges.

lax-pdxrecord

The all-time daily record rainfall in Portland is 2.69”; in LA it’s over twice that much at 5.88”. It’s never rained 3” or more in one day in Portland; there are 31 daily rainfall records greater than 3” in LA. The 4” mark has been hit ten times and 5” three times. LA’s daily rainfall record is greater than Portland’s for 165 days out of the year, despite Portland getting nearly 2.5 times the annual rainfall and being wetter in nearly every month, and LA being so reliably dry in summer that 19 days have never seen measurable rainfall and the last 140 Julys having delivered a grand total of 1.55” of rain.

The last 6 years are a reminder that for SoCal the faucet can turn on just as quickly as it turns off – and vice versa. The forecast for the next week or so is dry and in fact once, water year 1996-97, LA had no measurable rain between March 1 and the end of the water year. So now that I’ve sufficiently jinxed things, you’d better hope extra hard for some more drought relief this year!

SoCal Rain Update: One Step Forward

After 5 long years of drought, a series of powerful storms in January 2017 finally brought heavy rain and snow to California. The short-term impacts of the floods and mudslides have been well covered in the news, but many SoCal residents are wondering if the storms have made a major impact on the drought. Let’s take a look at where we stand in Los Angeles, and at water supplies around the state. As always, remember that in California we measure precipitation from October through the following September; this period is called the water year.

Currently, downtown LA is at 14.33” of rain for the water year. This is just 0.60” short of the yearly average, and already well past any of the drought years. In fact January 2017 alone brought more rain to LA than 3 of the 5 drought years, including last year’s completely ineffectual El Niño.

larain-graph-20170201larain-table-20170201

The six-year total for 2011-12 through 2016-17 is currently at 53.12”, which is 0.13” less than the record driest six-year period of 1958-59 through 1963-64. Over the last 10 years, we have a rainfall deficit of about 37”. So while this year has been good so far, to start making up lost precipitation from the drought, we still need the storms to keep rolling through over the next few months. Looking a little more broadly at SoCal, we can see that much of the region has fared better than LA.

Looking at major reservoirs in the state, almost all are doing very well. It already seems likely that the state will go into the summer with water storage facilities nearly full, and there’s still a lot of winter to come. Remember this the next time someone tells you there’s no reason to create more storage!

reservoirs-20170201

Taking a closer look at some southern California reservoirs of interest, Lake Cachuma, the largest reservoir for Santa Barbara County, was down to 7% of capacity last fall. This put cities in the area on severe water restrictions and prompted the city of Santa Barbara to reactivate its desalination plant. While this year has certainly replenished Lake Cachuma more than any of the drought years, it doesn’t seem like enough to ease restrictions yet.

cachuma-20170201

Over in the southern Sierra Nevada, Lake Isabella has finally received some much needed rain as well. This reservoir, on the Kern River above Bakersfield, is the largest in the Tulare Basin other than Pine Flat on the Kings River. Capacity is 568,000 acre-feet, so it’s nowhere near full, though storage is currently kept below maximum due to ongoing seismic improvements to the dam.

isabella-20170201

Looking at departure from normal precipitation to date for the water year across SoCal, we can see there’s been some drought relief in the south Sierra, the Coast Ranges, and the SoCal mountains.

wytotal-20170201

Precipitation indexes for the Sierra Nevada show it’s been a very wet year throughout the range. The north Sierra, corresponding to the Sacramento River drainage, has had 53.2”, already past the water year average of 50.0”, and on record pace (though the breakneck pace of January precipitation would be hard to match).

nsierra-20170201

The central Sierra, corresponding to the San Joaquin River drainage, is also already past the water year average, with 42.9” to 40.8”. It too is on pace to match some of the wettest years on record.

sanjoaquin-20170201

The south Sierra, corresponding to the Tulare Basin (Kings, Kaweah, Tule, & Kern Rivers), is just past the water year average, with 30.2” to 29.3”. It’s been a very wet year for the south Sierra, though it might be hard to keep up with 1968-69.

tulare-20170201

Looking over to the other side of California, the east Sierra, corresponding to the Owens Valley, snow water content has already passed April 1 averages, with 34.7” to about 24”. This is where the water in the LA Aqueduct comes from, so it’s good news for city water supplies, as we’ll have to buy less water from the State Water Project and Colorado River Aqueduct.

esierra-20170201

Peering into the next 7 days, the forecast calls for another round of solid storms for northern and central California.

gfs-20170201

Totals for the far south Sierra and SoCal look relatively modest for the next week… let’s hope that, like in January, this powerful NorCal storm is a prelude to strong rainstorms for us!

Editorial: all of the data used for this post came from public sources (National Weather Service, CA Dept of Water Resources, LA Dept of Water & Power). A lot of useful data is created and made available free to the public by government agencies that are going to have their budgets under attack in the coming years. So, you know… call your reps to protest when that happens!

SoCal Rain: A New Hope?

Last year, El Niño brought lots of rain and snow to northern California, but SoCal residents watched storm after storm pass us by, leaving us with a fifth year of drought. The five-year period 2011-2016 was by far the driest on record, with 38.79” of rain compared to the previous record of 45.63” in the drought of the late 1980s, and an average of 73.70”. (Remember that in California we measure precipitation from October through the following September; this period is called the water year.)

There’s been some positive press lately about the rainstorms we’ve had so far this winter, with December 2016 the wettest month for downtown LA since December 2010. This is true, though this December (4.55”) wasn’t really in the same league as December 2010 (10.23”). December 2010 delivered more rain in one month than any of the drought years other than 2014-2015, which was juiced by tropical storm remnants in September 2015.

Looking at this year in context, we are off to a good start, with 5.95” so far. That already surpasses the worst year of the drought (2012-2013, 5.93”) and is less than an inch away from last year’s final total.

larain-graph-20170101larain-table-20170101

While last month was encouraging, every drought year has had at least one respectable month of rain. We need about 8.5” more this winter, which would give us an average year, just to save us from having the driest six-year period on record. To start making up lost precipitation from the drought, we need the storms to keep rolling through the next few months, so let’s hope they do!

Looking a little more broadly at SoCal, we can see that much of the region has fared better than LA.

socal-departure-20170101

(Note: ignore the below normal precipitation along the immediate coast and just offshore, which is a systematic error in the map.)

San Diego County, Orange County, and the Inland Empire are all a little bit more above normal than we are in LA. The SoCal mountain ranges have done even better; the five light blue areas east of LA are the San Gabriel, San Bernardino, San Jacinto, San Diego County, and Santa Ana Mountains (starting top left and going clockwise). This is really good news for the forests and wildlife in SoCal’s wild areas.

The unfortunate exception is parts of the Ventura County and Santa Barbara County mountains in the Los Padres National Forest. Since these areas depend on local water supplies more than other parts of SoCal, they really need to catch up. Let’s hope the storms keep coming and that everyone gets their share of the action!