The final week of February, 2014, has begun, and the gentle hills and open fields around Thousand Oaks, Westlake Village, and Agoura are still a summertime brown. Typically there has been enough winter rain by this time of the year to turn our local hills a grassy green, but drought and sunshine have dominated Southern California thus far. Instead of being a chilly and muddy mess, my afternoon bike rides since November have been (almost without exception) on bone-dry trails in t-shirt-and-shorts weather! Sadly, or maybe not, our run of parched conditions appears to be ending later this week. Since I like to experience and record extreme weather and climate events, the prospects of a record dry rainy season were making me a little giddy of late. Remarkably, only 0.93″ has fallen into my rain gage since July 1, 2013, here in Westlake Village. The average seasonal rainfall around here is around 16 to 18 inches, with approximately 80 percent of that occurring from November through March. It is extremely unusual to go an entire “cool season” without a good-sized winter storm, though, and it looks like that is exactly what we are going to get on February 28 and March 1. A couple of inches of rain is forecast.
So, before Mother Nature gives us the business, I need to write about our dry spell. Most, if not all, of the (few) weather systems that have moved into Southern California this winter have been from the northwest. The area where I live (along the Los Angeles/Ventura county line) is rain-shadowed somewhat in these patterns. Weather fronts have a difficult time “holding together” as they move southeastward past Point Conception. We get much better rain amounts with storm systems from the west and southwest. The Conejo Valley and vicinity has been even drier than areas south of Los Angeles this season. Here are the monthly amounts at my home station in Westlake Village, beginning in July, 2013, when the current rain season began:
Feb 0.30″ (through the 25th)
These are astonishingly meager amounts: only 0.62″ for the season through December; only 0.63″ through January; only 0.93″ though February 25th. And, this is following an exceptionally dry first half of 2013. Only 3.20″ was observed from January to June of 2013. In all of 2013, my gage caught only 3.73″.
Of course, other area and regional weather stations have been very dry, too. Here are some season-to-date precipitation amounts (July 1 to Feb 25), from the National Weather Service:
Van Nuys 1.13″
Los Angeles/USC 1.20″
Los Angeles AP 1.27″
Long Beach 1.61″
Santa Barbara 1.79″
Santa Maria 0.94″
Paso Robles 1.41″
Santa Ana 1.25″
San Diego 2.60″
Palm Springs 1.26″
And here are some season-to-date precipitation amounts (July 1 to Feb 25), from (mostly) automatic Ventura County and Los Angeles County precipitation stations:
Conejo Valley area
Westlake Village (Reid) 0.93″
Cheesebro/Agoura RAWS 0.93″
Agoura (LA317) 0.79″
Thousand Oaks Civic Center 0.67″
Newbury Park 0.75″
Point Mugu (NTD) 0.33″
Ventura (County Government Center) 1.18″
Santa Paula Wilson Ranch 1.07″
Moorpark County Yard 1.17″
Simi Valley Sanitation 0.96″
Santa Monica Mountains area
Malibu Fire Station 0.35″
Calabasas Fire Station (LA474) 0.90″
Monte Nido Fire Station (LA 319) 0.94″
Topanga (LA318) 1.07″
San Fernando Valley area
West Hills (Bell Canyon Debris Basin) 0.75″
Woodland Hills Pierce College 1.17″
Simi Hills (Bell Canyon Rocketdyne) 0.98″
Northridge (LA463) 0.57″
Northridge (CSUN) 1.45″
Sepulveda Dam 1.41″
Pacoima Wash 1.46″
Keep in mind that these figures are not necessarily official and they might not be verified or checked for accuracy. The data are from automatic recording and transmitting equipment, which can and do malfunction. Occasionally some rain events are missed by stations that are not operating properly! For instance, the amount of 0.57″ at the L.A. County station in Northridge appears suspect when compared to the 1.45″ amount at nearby CSU Northridge. Nevertheless, the data show that most stations from Ventura to Van Nuys have had only one inch of rain or so since July 1, with the driest stations around 0.75″. There are a couple of stations with less than a half inch, but, call me Mr. Skeptical.
The question which should be running over and over in your head RIGHT NOW is:
“Bill, just how unusual is it to have such miniscule seasonal rain amounts this late into the rain season? Thank you in advance for your comprehensive, thoughtful and timely response.”
Excellent question, and you are quite welcome! In order to answer this, we need to go into the dark recesses of the William Reid climate data archives. There are no long-term weather stations in the Conejo Valley area, but there are some nearby. Monthly precipitation tables are available for Pierce College in Woodland Hills, in the western San Fernando Valley, with data beginning in July of 1949. As recently as the season of 2006-07, only 4.04″ of rain was observed (for July-June). During that season, there was only 0.90″ through December, 1.56″ through January, and 3.44″ through February. Our nifty table above shows that only 1.17″ has landed in the rain gage at Pierce College during the current 2013-14 rainfall season.
There have been numerous seasons at Pierce with less than one inch through December. Both 1958-59 and 1962-63 had rainfall amounts of only 0.18″ for the first six months of the season. The season of 1956-57 had only 0.36″ by December 31, and 1975-76 and 2000-01 both had 0.38″. The season of 1990-91 had 0.57″ through December. Maintaining a very low seasonal total through January and February is rare, however.
Low seasonal amounts at Pierce through January include 0.71″ for 1962-63 and 0.38″ for 1975-76! For 2013-14, only 0.89″ had fallen through January. These are the only seasons at Pierce College since 1949 with under one inch of precipitation through January.
As for lowest seasonal amounts through February at Pierce, the 1962-63 and 1975-76 seasons were both doomed by four-inch Februarys. In February 1963, a big storm on the 9th jacked up the seasonal amount to more than four inches. In February 1976, four inches fell in the first ten days of February — goodbye record dry season. The 2006-07 season had only 3.44″ through February: were any others drier? No! The season of 1999-2000 had only 1.96″ through January, but then February was very wet beginning on the 10th (more than 6 inches for the month). In 1998-99, the amount through February was only 3.58″, slightly more than that for 2006-2007. As you can see, it is rare to make it this far into the rainfall season with only 3 or 4 inches of precipitation. Pierce College’s current “seasonal rainfall to date” amount of only 1.17″ (through February 25!) is practically “off the charts” on the low side, and we are talking a 65-year period of record! The amount is about one-third of the “through February” value for record-holding 2006-07. Is it asking too much to delay that big weekend storm a day or two?! If Pierce College receives less than 2.27″ additional rainfall before the end of February 28, 2014, then 2013-2014 will have the driest July-February period on record there.
Before I wrap this up, let’s look at similar data for downtown Los Angeles, where records began in 1877. Los Angeles has received only 1.20″ from July 1, 2013 to February 25, 2014. In 2006-07, Los Angeles collected only 2.42″ from July to February. Even lower is the 1.82″ through February for 1923-24. Other very dry July to February seasons at Los Angeles were 1898-99 (2.98″), 1903-04 (3.25″), 1947-48 (3.21″), 1924-25 (3.50″) and 1962-63 (3.52″). So, as at Pierce College in Woodland Hills, the miniscule “season-to-date” amount of only 1.20″ through February 25 at Los Angeles is firmly in record territory. But, more than an inch of rain appears likely at Los Angeles before March 1, and that would shove the seasonal amount well above the current July-February “low end” record holder: 1923-24, with 1.82″.
By the way, Los Angeles had 3.42″ in March 1924, including 1.24″ during the first five days of that month, totally ruining that record dry season.
For another day or two I can enjoy the current paltry precip amounts for 2013-14. After that it looks like another record dry season will go down the drain. I doubt that I’ll be around if it takes another 90 years for our next chance.
Here is a great supplement, provided by my weather and climate colleague Chris Crabtree of Santa Barbara:
• So far this season, downtown Santa Barbara has received 1.6” of rain - the driest season to date on record (starting in 1867) – 146 years. The average for this point in the season is ~13.7”. • I have recorded only 6 days of measurable rain so far this winter at my house. First day 11/21 and most recent 2/6. To go backwards in time and accumulate 2” of rain, have to go back to 3/31/13. In other words, WE HAVE RECEIVED ONLY 2” OF RAIN IN THE LAST 11 MONTHS. • The next driest season on record to date was 1897-98, when 2.1” of rain fell thru Jan (1.4” fell in Feb that year). That season recorded only 5” of rain. • Our driest year on record occurred in 1876-77, when only 4.5” of rain fell.