Category Archives: nature|weather

Long Shadows, Cool Canyons

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.

La Nina and the 2010-2011 Southern California Precipitation Outlook

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.

Subtropical Flow from an Upper Low

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.

The Heat Was Hot

Record heat in Southern California

Today at 12:15 p.m. PDT the temperature at Downtown Los Angeles (USC) reached 113°F (45°C), which is the highest temperature recorded downtown since weather recordkeeping began in 1877.

It wasn’t quite as hot in the San Fernando Valley. The high temperature at Pierce College reached 110°F.

When I started my run at Ahmanson Ranch it was 106°F. I took two bottles with ice water. One was used to keep my arms, legs and head/neck wet. With the relative humidity low, this was very effective for cooling. I picked a 45-50 minute course that was not too strenuous, and kept the pace moderate.

It was a surprisingly moderate run, but I sure wouldn’t want to run out of water or have some other problem when the temperature is that high!

Running Hot & Cold

Mt. Baldy from the summit of Mt. Baden-Powell

Mt. Baldy fron the summit of Mt. Baden-Powell

Yesterday, Woodland Hills topped the 90° mark for the first time this year. But somebody forgot to tell the local mountains about the warmup. This morning, I was about a mile into an out and back trail run from Islip Saddle to Mt. Baden-Powell, and with the wind chill, it felt like the temp was in the 40’s.

It was chilly in running shorts, and I debated pulling some warmer clothes from the pack. In addition to a short-sleeve shirt, I did have on a pair of pull-on long sleeves. For the moment that seemed to be enough. Rounding a corner, the trail leveled, and up ahead I could see a hiker headed my way. Based on the time, I figured he was descending from Little Jimmy Campground. We exchanged greetings, and as we passed, he commented, “you know there’s a lot of snow on the trail.”


Snow on the crest near Mt. Baden-Powell
This Spring the weather in California has been dominated by a series of cool troughs, slowing the snow melt and in some cases adding to it. It its May 27th Summary of Snow Water Content, California Cooperative Snow Surveys reported the statewide snowpack at nearly twice the normal amount for the date. Squaw Valley reopened for Memorial Day weekend; and with over 100 inches of snow since April 1, Mammoth Mountain plans to operate through July 4.

On the shaded, north facing slopes of Mt. Islip there was more snow than I’d seen since the Spring of 2005.  It couldn’t be avoided. However, the route was well-traveled, and where there was snow, dirt-covered steps eased the way. I had picked up a short length of downed fir, and it worked OK as a crude ice axe, or if you prefer, a stubby trekking pole. It enabled me to move a little faster, and had the added benefit of keeping my upslope hand out of the snow.


Seedling Jeffrey Pine in ghost forest
It didn’t take long to reach Windy Gap (7588′), and soon I was working up the trail to the gap above Windy Gap. Here the trail winds through a ghost forest of old growth trees, burned in the 2002 Curve Fire. Recovery has been slow, and it was heartening to see a young Jeffrey pine in the midst of all the deadwood. It also gave me a sobering perspective of the time that was going to be required for the recovery of the forests decimated by the Station Fire.

The trail climbs up to the crest of the San Gabriels near peak 8426, about a mile east of Windy Gap. From here it more or less follows the prominent divide all the way to Mt. Baden-Powell (9,399′). It’s the “more or less” part that’s key in a snowy year. The shaded north side of the divide may be completely snowbound, while the crest and south side are snow free. The way the ridgeline is oriented, storm winds create deep bands of snow along and just north of the crest. In places the trail can be buried in several feet of snow.


Snow on the crest east of Mt. Burnham
On the east side of Mt. Hawkins I checked out a tree that had been struck by lightning, and then continued along the ridge. The wind was little more than a breeze now, and the temperature comfortable. I pulled off my running sleeves, and then followed the trail across the warm, south facing slopes of Throop Peak. Sometimes on the trail, and sometimes on the crest, I descended to a saddle and then climbed up and over Mt. Burnham (8997′).

On the summit of Mt. Baden-Powell there was almost no wind. The sun was warm and the air clear. Across Vincent Gulch Mt. Baldy gleamed alpine white, its summit ridges still heavy with corniced snow. Many miles to the east, snow could also be seen on San Gorgonio Mountain, and Mt. San Jacinto. A Clark’s nutcracker complained raucously from the top of a Lodgepole Pine, and I assured the bird that I would be leaving the summit soon.

Some related posts: San Gabriels High Five, Islip Saddle – Mt. Baden-Powell Out & Back

May… or March?

Eagle Rock From Eagle Springs Fire Road

Eagle Rock From Eagle Springs Fire Road

Is it May or March? With all the blustery weather systems that have been moving through Southern California, it’s been hard to tell.



Today I had planned to head back to the high country of the San Gabriels, but instead decided to take advantage of the spectacular weather and do a rambling 24 mile run in the Santa Monica Mountains.

It was a good choice. Early in the run growing mountains of silver-lined cumulus towered above the Hub, and a brisk wind tempted me to pull the sleeves from the pack. Wildflowers lined the trails, and the chaparral teemed with color, sound and scent. It was a long run kind of day.

Note: Later in the day I talked to a runner who had been at Lake Arrowhead early in the morning. He said it had been snowing down to 3000 ft! According to the NWS, record low temperatures for today were set at Lancaster (41°), San Luis Obispo (38°), and Sandberg (28°).