Category Archives: weather|southern california

nature, nature|clouds, nature|weather, photography, photography|landscape, weather, weather|southern california

Jet Stream Cirrus

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Jet stream cirrus

The long streaks in the photograph above are cirrus clouds embedded in a 125 kt jet stream that was positioned over Southern California Thursday afternoon.



The jet stream was at an altitude of about 30,000 ft. and associated with an upper level low pressure trough off the coast. This trough is the source of the disturbances that are resulting in our latest bout of wet weather.

The jet stream is a key feature of the earth’s atmospheric circulation, and plays an important role in both weather and climate.

For more about jet stream cirrus see A Composite and Microphysical Study of Jet Stream Cirrus Over the ARM Site.

The photographs are from a trail run on Thursday.

nature, nature|clouds, nature|weather, photography, photography|landscape, running, trails, weather, weather|southern california

Satwiwa Shadows & Sun

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Satwiwa from Danielson Rd.

By the time I reached Rancho Sierra Vista/Satwiwa at the end of last Sunday’s wet run to Serrano Valley and back, the frontal band was mostly done with its showers and was speeding to the east. In its wake were blustery winds, broken clouds, and a dynamic patchwork of sun and shadow on Satwiwa’s spectacularly green landscape.

nature, nature|weather, photography, photography|landscape, running, running|adventures, trails, weather, weather|southern california

Showery Sunday

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Boney Mountain from the Old Boney Trail

Boney Mountain from the Old Boney Trail

It started to sprinkle as I walked from my car to the Wendy Drive trailhead. In a matter of minutes the sprinkles turned to a light, but steady rain, and the Satwiwa trail started to become slick with mud. The rainy weather would continue through most of my run in Pt. Mugu State Park.



It was wet today, but today’s rain was the first in Southern California in nearly a month. Southern California was very wet from October through December, but the storm door from the Pacific into California slammed shut in early January. The weeks of wet weather followed by weeks of warm, dry weather has the plant communities of the Santa Monica Mountains thinking it’s Spring.

Among the flowers blooming along the Old Boney and Serrano Valley trails were paintbrush, encelia, milkmaids, phlox, shooting star, nightshade, wild cucumber, canyon sunflower, deerweed, and bigpod ceanothus. But more than the plants have responded. On January 17, trail runner Howard Cohen took this video of a sizable rattlesnake on the Old Boney Trail!

Some related posts: Serrano Valley from Wendy Drive, Serrano Valley from the Chamberlain Trail

nature, photography, photography|landscape, running, trails, trails|smmc open space, weather, weather|southern california

Chumash Trail Green

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Chumash Trail in Simi Valley

It’s now been 17 days since there’s been measurable rain at Downtown Los Angeles (USC). A trace of rain was recorded on a couple of days, but for the time being a big blocking ridge has shut the door on Pacific precipitation.

So far this January, only 0.58 of rain has been recorded, which is a little less than one-third of normal for the month. However, because of our frequent December storms the water year total at Los Angeles is currently about double the normal amount — and why open space areas of Southern California have turned so lush and green.

nature, nature|weather, photography, photography|trail running, running, running|adventures, trails, trails|smmc open space, weather, weather|southern california

Bandit Training

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Top of the Wildlife Corridor Trail

What a difference 5 days makes! In the cold morning shadows before the start of the Boney Mountain race last Sunday, the dew on the fences was frozen and frost was everywhere. This morning in Corriganville Park the temperature was a balmy 65 or so, and the high was expected to be around eighty.

Today I was running the Bandit 30K course as part of a training run organized by Bandit 15K/30K/50K R.D. Randy Shoemaker. Good thing too. Even though these are my backyard trails, it reminded me just how tough these courses are. The numbers — about 3300 ft. of gain/loss over 19.5 miles for the 30K — don’t tell the whole story.



The title photograph is of runners at the top of the Wildlife Corridor Trail. This gnarly trail links Corriganville Park to Rocky Peak Road, and it is just one of the special treats you’ll encounter on the 15K, 30K and 50K courses. I don’t know if it tougher going up, when your legs are fresh; or going down, when your legs are worked. From personal experience I know it is really easy to push too hard on this climb, and mutter to yourself, “Why did I do that?” for the remainder of the race.

Today, the conditions could not have been better. Well, if we’re going to nitpick, maybe a little less wind. But who can complain on a January day when skies are blue, the hills are green, and the temperature is in the seventies?

nature, nature|clouds, nature|weather, photography, weather, weather|southern california

Mammatus Clouds Over the San Fernando Valley

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Mammatus Clouds Over the San Fernando Valley

These rare clouds — a mid-level form of mammatus — were over the western San Fernando Valley last Thursday afternoon, January 6, 2011. They were produced by the moisture and dynamics associated with a closed upper level low that was about 390 miles WSW of Los Angeles, and moving ENE at about 17 mph.

I first noticed the mammatus clouds around 3:30 p.m. About 30 minutes later, when I started my trail run in the Simi Hills, the cloud band had shifted a couple of miles to the WNW, but the mammatus was still present. The title photograph was taken just a few minutes into the run, at about 4:07. This uncropped version of the image shows the clouds in relation to the terrain.



The mammatus was in the leading band of a series of cloud bands slowly moving from the ESE to the WNW. Over the next 30 minutes the mammatus mostly dissipated, as the cloud band became disrupted by shear. During this period the bands evolved into a wave-like sequence of bulbous clouds that had some of the characteristics of mammatus, but were not multi-lobed. The bases of these clouds were ragged — an indication that snow showers were sublimating in the dry air below. The photograph of the cloud sequence was taken at about 4:37 p.m. Some remnants of mammatus could still be seen in the sheared leading band.

The circumstances in which mammatus is observed and some possible mechanisms for its formation are discussed in the 2006 paper, The Mysteries of Mammatus Clouds: Observations and Formation Mechanisms by David M. Schultz, et al.

Based on a NAM analysis for Van Nuys and NKX (San Diego, CA) sounding, the atmospheric profile was consistent with real-time soundings when mammatus is present. A BUFKIT model sounding based on NAM data for 4:00 p.m., shows a moist layer from about 14,000 ft. to 23,000 ft., with a dry subcloud layer. The freezing level was indicated at about 8500 ft. A plot of vorticity from NAM data indicated a vorticity lobe in the area at the time the clouds were observed. As can be seen in both photographs, there was also strong shear between 20,000 ft. and 25,000 ft. A superadiabatic subcloud layer is not present in the soundings, but cooling from subcloud evaporation or sublimation might create one.

The photograph in the post Simi Hills to the San Gabriel Mountains was also taken on this trail run.