Category Archives: weather

nature, nature|clouds, nature|weather, photography, photography|landscape, weather

Oak, Hill & Wave Clouds

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Mountain wave clouds

These mountain wave clouds were produced by north-northeast winds blowing across the generally east-west oriented mountain ranges north and northwest of Los Angeles. The clouds form near the crests of the undulating airflow downwind of the mountains.

The cirrus veils trailing downwind from the clouds are comprised of ice crystals. There was little shear, so the wisps and sheets of cirrus are aligned with the wind and perpendicular to the long axis of the cloud. Compare to the cirrus veil of these lenticular clouds, also formed by north-northeast winds, but which were being sheared by northwesterly winds.

From a trail run at Ahmanson Ranch on Thursday.

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.

nature, nature|weather, photography, photography|landscape, running, weather, weather|la nina, weather|southern california

Departing Storm

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Departing Storm

As skies cleared Monday afternoon, we thought we had put a wrap on the wet weather — at least for a while. But the Sunday-Monday system left a cutoff upper low spinning off the coast of Southern California, and as that low moves east over the next couple of days it could produce some showers.

That’s the way it’s been this rain season. Looking back through NWS rainfall data, since October 1 we’ve gone no more than 10 days at a stretch without measurable rain at Downtown Los Angeles (USC).

Even if our weather becomes more typical of what occurs during a La Nina episode, 81% of our normal annual rainfall is already in the bucket. To have an average year all we need is 2.86 inches between now and June 31. Downtown Los Angeles normally records about two-thirds of its annual rainfall in the months of January, February and March — around 10 inches — so (theoretically) 2.86 inches shouldn’t be hard to do. But we’ll see!

The title photograph is from a run in the Simi Hills on Monday.