Category Archives: nature|weather

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.

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

Las Virgenes Creek Near the Sheep Corral Trail

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Upper Las Virgenes Creek

At the start of my run East Las Virgenes Canyon was deep in shadow, and it was cold, cold, cold. At least by Southern California standards. But it would be warm enough, soon enough, and being a little chilly now would make the sun feel even better when I escaped from the canyon. The good news was the temperature was near freezing, and the muddy sections of dirt road in the canyon were mostly frozen.

I was doing a run I often do before a race, or when I want to back off the distance and elevation gain a bit — a 13 mile route from the Victory trailhead at Ahmanson Ranch, through Cheeseboro Canyon. The route starts the same as the run to Simi Peak, but when you get to Shepherds Flat, you turn left (south) down Cheeseboro Canyon.



Picking up the pace to try and generate some warmth, it took about 30 minutes to get to Las Virgenes Canyon. In another 15 minutes or so, I had forked left off the dirt road onto the Sheep Corral Trail. This singletrack trail meanders through live oaks along upper Las Virgenes Creek before working up and over to Shepherds Flat.

For the first time in several years, this part of Las Virgenes Creek was flowing. The last time it had more than puddles of water was during the record setting El Nino rain season of 2004-2005. That year Downtown Los Angeles recorded more than twice it’s normal amount of rainfall.

At the six mile point I reached the junction at Shepherds Flat and turned onto the Sulfur Springs Trail. With the exception of one very wet section, Cheeseboro Canyon was mostly in good shape. There was still some ice on the mud puddles in the lower part of the canyon.

Keeping my shoes mostly dry and mud free had become kind of a game, but a game I was destined to lose. When mud thaws it becomes incredibly sticky, and that happened on the connector that links Cheeseboro Canyon to Las Virgenes Canyon. It was like running in 5 lb. Hokas.

The worst of the unavoidable mud ended at Las Virgenes Canyon, and after another 30 minutes or so of dodging mud puddles, I was back at the Victory trailhead. It was a fun run and a great way to start the New Year.

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

New Year’s Eve Harbinger of Rain

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Foretelling the approach of a system forecast to bring wet weather to some areas north of Pt. Conception New Year’s Day, and Los Angeles Sunday, this thick cirrus cloud shield is associated with the circulation around a low a few hundred miles off the Pacific Northwest coast.

Wednesday’s cold front, the latest in a series of surprisingly frequent December weather systems, increased the water year rainfall total at Downtown Los Angeles (USC) to 11.70 inches. As of today, L.A.’s rainfall total is about 8 inches above normal, and more than three times the normal amount of rainfall for the water year to date. For the first six months of the 2010-11 water year, the rainfall total for Downtown Los Angeles is the fourth wettest in the 133 years that records have been kept. The water year starts on July 1 and ends June 30.

The photograph is from today’s run on the Chumash Trail and Rocky Peak Road, northwest of Los Angeles. It was cold on the north facing sections of trail that don’t see the sun this time of year. Inch long needle ice crystals had formed along the margins of the trail in several places.

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|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

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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.