Category Archives: weather|southern california

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

Long Shadows, Cool Canyons

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Valley oak

It’s that time of year. Willows and wild walnut trees are showing some Fall color, and the valley oaks are losing their leaves. Even on a warm day, the long shadows, clear skies and low humidity of late Autumn cool the hillsides, generating chilled katabatic flows down gullies and canyons.

As temperatures warmed up this week I took a probe thermometer on my afternoon trail runs at Ahmanson Ranch (Upper Las Virgenes Canyon Open Space Preserve) and measured the temperature of some of these invisible streams.

My general weather data reference for the area is the Cheeseboro Remote Automated Weather Station (RAWS). The high temperature at the Cheeseboro RAWS ranged from 73°F on Tuesday to 75°F Thursday. The temperature in the shade at the Victory trailhead parking lot at the beginning of my runs (around 4:00-4:15) was about 70°F.

Tuesday, the temperature on the road about 1.1 miles from the parking lot, and above East Las Virgenes Canyon was about 69°F. A quarter-mile away, down in the dry streambed, the temperature was a chilly 47°F — a drop of 22°F.

Wednesday, I ran to upper Las Virgenes Canyon. The temperature at a saddle above the canyon was 66°F. Down in the canyon near one of the stream crossings, the temperature was 45°F — a difference of 21°F.

Thursday I ran back to the same point in Las Virgenes Canyon. Even though the high temperature for the day was about the same as Wednesday, the humidity was higher, and there were some high clouds. The katabatic flow was not as well-defined, and the temperature drop was only about 13°F.

Conditions during the week were not especially favorable for hillside radiational cooling, and I expect temperature differences of 30°F might be possible in ideal circumstances. In any case it feels like that in running shorts and a short-sleeve shirt.

nature, nature|environment, photography, photography|wildflowers, weather, weather|southern california

Early Bloomers

published
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Wishbone bush (Mirabilis californica)

This autumn, the first measurable rainfall at Downtown Los Angeles was on October 4, 2010. Since then we’ve seen some rain in Southern California every 7 to 10 days or so. The storms haven’t been huge, but many locations have recorded near to above average rainfall for the water year to date. Some, like Santa Barbara and San Diego, are well above normal for the date.



Because of our erratic weather, many Southern California plants are opportunistic and will shift their growing and flowering season to take advantage of wet weather.

Discounting plants that normally bloom in autumn, one of the earliest of the early bloomers this autumn was this bigpod ceanothus in Pt. Mugu State Park, photographed on November 14. Another early bloomer was Wishbone Bush which was beginning to bloom in the Simi Hills on November 21. This Shooting Star was photographed at Sage Ranch on November 30. In the past couple of weeks I’ve also seen Prickly Phlox, Bush Monkeyflower and Wild Cucumber in bloom.

The title photograph is Wishbone Bush on the northeast ridge of Ladyface last week.

Some related posts: Wishbone Bush, Shooting Stars, California Prickly Phlox, Bush Monkeyflower

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

Oaks, Grass & Sun

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Oaks, Grass and Sun

It’s unusual to see this much green in Southern California in mid November. The growth is the result of a wet October, with some areas recording several times the normal amount of rainfall.

Although water year rainfall totals for many areas of Southern California are still near or above normal for the date, November is the customary start of the rain season, and so far this month, we’ve been drier than normal.

That might change this weekend. Models have been having a tough time with the evolution of a low and trough that is already producing rain and snow in the Pacific Northwest. In true La Nina fashion, the high amplitude flow might result in the southern part of the trough being more offshore (wetter), or more onshore (drier), as it sets up over the West. We’ll see!

The photograph is from this afternoon’s run in the Simi Hills.

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

Boney Mountain Morning

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Crags on Boney Mountain's western ridge.

The face was not steep, but I was glad the pockmarked volcanic rock had big holds. Rainwater filled some of the pockets, and patches of lichen and moss on the face were saturated and slippery. It wasn’t a runout climb at the Needles or Tuolumne Meadows, but gravity still worked the same way. I reminded myself not to do something “stoopid.”



At the top of the face I looked around and sighed, and then looked around and sighed again. It was another stunning morning on the western ridge of Boney Mountain. To the west a nearly full moon struggled to remain above the hills, its brightness veiled in a mix of clouds. Another storm was expected in the evening, and the sky told of its approach. Broad strokes of cirrus brushed the blue above, and here and there fingers of tattered stratus reached into the coastal canyons and clung to the wet hillsides.

Today’s forecast for the Santa Monica National Recreation Area had called for mostly cloudy skies, and a high in the 60s. At the moment it was mostly sunny, but already there were hints of clouds developing on the ridges and mountaintops. At some point in the day the clouds would envelop the mountains, and transform the morning’s expansive vistas into a dimensionless gray. I hoped to get up the ridge, over Tri-Peaks, and to Sandstone Peak before that happened.



By chance the clouds behaved, and the splendid views and weather continued all the way to Sandstone Peak, and beyond. The run back to the Wendy Drive trailhead on the Backbone, Sycamore Canyon, and Upper Sycamore trails could not have been better.

As I climbed the final little hill to the parking area I noticed I had no shadow. Over the course of the afternoon the cloud deck would continue to lower and thicken, and by evening light rain would begin across the area.

Some related posts: Clouds and Crags, Conejo Valley Sun and Boney Mountain Clouds, Sandstone Peak from Wendy Drive

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

La Nina and the 2010-2011 Southern California Precipitation Outlook

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Clouds on Rocky Peak road

The second of two vigorous upper level lows to batter Southern California this Autumn has pushed the water year rainfall totals for many stations around the area to above normal.  Does that mean we’re likely to see the wet weather continue through the 2010-2011 rain season?



Probably not. Since last Winter, ENSO conditions in the equatorial Pacific have flip-flopped. The Multivariate ENSO Index (MEI) has plunged from the fifth strongest El Nino for Feb/Mar to the strongest La Nina for Aug/Sep. The Aug/Sep value of the MEI is the lowest since Jul/Aug of 1955. Generally, El Nino conditions result in wetter weather in Southern California, and La Nina drier.

A precipitation composite for eight years in which ENSO was transitioning from El Nino or Neutral conditions to La Nina indicates that “on average” the coastal Southern California climate division recorded about 4 to 5 inches less precipitation than normal for the period November through March. The percent of normal water year rainfall recorded at Downtown Los Angeles (USC) ranged from a low of 53% (1988, 8.08″), to a high of 99% (1973, 14.92″). The average rainfall for these years was 77%, or 11.7″.

Maps generated using the ESRL/PSD page Risk of Seasonal Climate Extremes in the U.S. Related to ENSO do not indicate a higher than normal risk for an extremely dry rain season in Southern California when La Nina conditions are present.


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La Nina composites from CPC’s ENSO Temperature & Precipitation Composites page suggest the period Jan-Feb-Mar may be particularly dry, but this is not reflected in CPC’s official seasonal precipitation forecasts.

CPC’s Three-Month Precipitation Outlooks and NOAA Winter Outlook were updated yesterday. The precipitation outlook for Nov-Dec-Feb in the Coastal Southern California climate division shows equal chances of above average, near average, or below average precipitation. As the rain season progresses, these probabilities become only slightly skewed toward below normal precipitation. The skew becomes more pronounced in Feb-Mar-Apr when the probability of below normal precipitation increases to 45%.

The title photograph is from Sunday’s out and back run from Chatsworth Reservoir to Rocky Peak.

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

Subtropical Flow from an Upper Low

published
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Hot on the heels of our record setting Autumn heatwave, an upper level low off the coast has been spinning subtropical moisture into Southern California. The unstable weather has produced some impressive clouds, isolated showers, strong thunderstorms, as well as a few rainbows. This thunderstorm development is north of Los Angeles.

From today’s run in the Simi Hills.