We’ve had some great running weather in Southern California this Spring, with more than our usual share of cool days and postcard skies. Remarkably, the highest temperature recorded at Downtown Los Angeles so far this year was in the final few days of Winter, when the temperature hit 88 on March 16.
The title photograph is from a recent run in the Simi Hills.
I heard a news report the other day that Southern California’s rain season would end in two weeks. While Southern California typically receives the bulk of its precipitation in the months of November through April, the rain season doesn’t turn off like a switch on May 1. There certainly can be significant rain in May, and even June.
The water year for Downtown Los Angeles (USC) is from July 1 to June 30 of the following year. So far, Downtown Los Angeles (USC) has recorded 16.17 inches of rain during the current water year. This is more than an inch above the 1971-2000 annual climate norm for Los Angeles of 15.14 inches.
Our Sunday-Monday storm put Downtown Los Angeles at 1.51 inches of rain for the month of April — well above the climate normal of 0.83 inches. The normal amount of precipitation for May is 0.31 inches, and for June is 0.06 inches. But those are just averages. On occasion we receive much more than this, and sometimes much less. On the up side, according to NWS data, in April 1965 Los Angeles recorded a total of 6.02 inches of rain. In May 1921, 3.57 inches was measured; and in June 1999 0.98 inch was recorded.
Although the current El Niño has weakened, convection is still somewhat enhanced in a broad region of the equatorial Pacific, and the MEI, ONI, and GWO indicate the continued presence of El Niño. This could result in more active Spring weather than usual, and more opportunities for rain in Southern California.
At the moment, the next opportunity for some Southern California rain looks to be next week, around Tuesday or Wednesday. We’ll see!
The title photo is from a run on the Chumash Trail at the end of March.
Because of their unusual “flying saucer” appearance, lens shaped lenticular clouds have long drawn attention. According to a research article in Weather, depictions of wave clouds appear in Gothic art from the 15th century.
Lenticular clouds typically form when wind flows into, and then up and over a mountain range, creating a series of “roller coaster” atmospheric waves downwind of the range. Lenticular clouds can (but don’t always) form in the peaks of the waves, as a layer of air rides up a wave, and cools and condenses. The waves are called standing waves because the peaks and troughs can stay (more or less) in the same place for hours at a time.
The rising air on the windward side of a lee wave can be soared by gliders to high altitudes. According to the FAI, the current world absolute altitude record for gliders is 15,460 meters (50,722 ft.). This record was set by the late Steve Fossett in 2006, soaring a mountain wave in the Andes. Mountain wave soaring was pioneered on the east side of the Sierra, and several single place sailplane world altitude records have been set soaring the Sierra wave.
Lee waves also have a nefarious side. Rotors, breaking waves, and other phenomena associated with mountain waves can create extreme turbulence. A sailplane destroyed in early research on rotors was estimated to have experienced 16 g of acceleration. According to the Australian Transport Safety Bureau, “clear air turbulence associated with a mountain wave ripped apart a BOAC Boeing 707 while it flew near Mt. Fuji in Japan. In 1968, a Fairchild F-27B lost parts of its wings and empennage, and in 1992 a Douglas DC-8 lost an engine and wingtip in mountain wave encounters.”
The wave clouds above were photographed northwest of Los Angeles during a trail run earlier this month. The wind forming the wave clouds appears to be from the north-northeast. The situation was peculiar because the wind at nearly all levels at that time was from the northwest. The tops of the wave clouds are being sheared by winds blowing from the northwest (left to right).
Here’s an animated series of NRL satellite photos showing the waves pictured above, and the complex wind and wave pattern at the time of the photograph.
Pushed up and over Boney Mountain’s two thousand foot western escarpment, Pacific winds condense into thick cloud along its jagged crest. At times breaking free of the mountain’s grasp, patches of cloud drift eastward, creating a patchwork of sun and shadow on the steep slopes, and in the valley below.
In the distance, the Ventura Mountains gleam with a mix of snow and cloud, and below the fields of Satwiwa stand out vibrant and green. At my feet hundreds of purple shooting stars dance in the wind; and nearby yesterday’s rain seeps and trickles from moss to lichen on the scraggy volcanic rock.
It is a remarkable morning, and an exceptional one to be doing the Boney Mountain north side loop. Here’s a short video of some of the views along the way.
The weather has calmed in Southern California. Medium range models are forecasting a break of about a week in what has turned out to be a very busy rain season. Over the last 90 days a precipitation pattern typical of El Niño has emerged in the western U.S. This is reflected in rainfall total for Downtown Los Angeles (USC), which is now at 13.2 inches for the water year — 4.78 inches above normal.
The dry weather could not have come at a better time for those affected, or threatened, by mudslides and debris flows. This small slump along a road at Ahmanson Ranch is indicative of the instability that can develop when soil becomes saturated. Had our recent wet pattern been more persistent, mudslides and debris flows might have been much more widespread and devastating.
One of about a dozen vernal pools in the Rocky Peak area. More than just a puddle, these rainy season pools form as a result of the area’s unique geology.
In my experience, excessive rainfall is not necessary for the pools to form. Normal month-to-month seasonal precipitation is usually sufficient. Their persistence depends on several factors, but in a season with normal to above average precipitation, the pools can last for several months.
From Wednesday’s run on Rocky Peak.
Related post: Vernal Pool at China Flat