Category Archives: weather

Lenticular Wave Clouds

Lenticular wave clouds northwest of Los Angeles.

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.

Conejo Valley Sun and Boney Mountain Clouds

Conejo Valley from the north side of Boney Mountain.

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.

A Welcome Break in a Busy Rainy Season

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.

Clearing Skies

Six days of rain had finally come to an end. Soaked hillsides steamed in the morning sun; but still in shadow, tussocks of grass along the dirt road wore a thick coat of frost. Running west on the main drag in Ahmanson Ranch, we were working our way over to Cheeseboro Canyon.



Whether the conditions were imperfect or perfect was a matter of perspective. Yes, it had been a little muddy and wet, but that was part of the experience, and part of the morning.

In some places droplets of water refracted and reflected tiny spectra of color, while in others flat plates of frost glittered in the sun. Running along a rejuvenated creek, the smell of wet earth mixed with the rich organic odors of old willow leaves and other vegetation.

Away from the trailhead there was not a hiker, runner, rider or mountain biker to be seen. Remarkably, even in Cheeseboro Canyon no one was on the trail.

Sometimes I’m asked,”What are you training for?” Being able to enjoy a run like today’s is my reply.

Pattern Change Ahead

Patterned altocumulus clouds near Los Angeles

Computer models and other tools continue to forecast a shift to an “El Nino like” upper flow pattern next week that could result in an extended period of wet weather in Southern California. I’ll be updating Southern California Weather Notes on Wednesday with additional info.

The photograph of patterned altocumulus clouds is from this afternoon’s trail run along the northern boundary of Ahmanson Ranch, near Los Angeles.