Category Archives: clouds

An Upper-Level Low Sunrise, Shower, and Sunset

Sunset in West Hills, CA, associated with an upper-level low off the coast of Southern California.

It was about 15 minutes before sunrise when I started my run from the trailhead at the “Top of Reseda.” After running up to Mulholland and partway down Fire Road #30, I could see a batch of tropical-looking clouds to the southeast. These were associated with a cutoff upper-level low that had formed off the coast of Southern California on Halloween.

The behavior of cutoff upper-level lows is difficult to forecast. They are usually separated from the general west to east flow and typically wobble around like a spinning top. A cutoff low can remain off the coast for several days or more. Just where they wobble can dramatically impact the weather. So far this morning, the only effect of this weak low had been to embellish the sunrise with a few clouds, but such lows can be capricious, and this one was no exception.

My first stop was going to be Temescal Peak, and I picked up the pace a bit, curious to see how the clouds and sunrise might look from that viewpoint. Temescal Peak is just off the Backbone Trail, near its junction with Fire Road #30/Temescal Ridge Fire Road. On a clear day this tiny peak affords an exceptional 360-degree view that can include Mt. Baldy, San Gorgonio Mountain, San Jacinto Peak, Mt. Pinos, Hines Peak, and other area landmarks.

Sunrise over West L.A. from Temescal Peak in the Santa Monica Mountains.
Sunrise over West L.A. from Temescal Peak in the Santa Monica Mountains.

Turning left at the Hub, it didn’t take long to get to Temescal Peak. Westward from the peak, a veil of smoke could be seen in the vicinity of the Maria Fire. Nearby, some of the canyons in the area of the Getty Fire were filled with a smoky haze. In the distance, a few mercurial clouds were scattered across the eastern sky.

At the time, I couldn’t tell if the clouds were approaching or receding, developing or dissipating. Returning to the Hub, I turned left on Eagle Springs Fire Road and began the descent toward Trippet Ranch. On the way, it became clear the clouds were headed my way. By the time I’d run to Trippet Ranch and up to the top of the Musch Trail, the band of clouds covered much of the eastern sky.  Virga streamed from the bases of some of the clouds, and  I wondered if a few rogue drops might be reaching the ground.

Developing clouds associated with an upper-level low along the coast of Southern California.
Developing clouds from near the top of the Musch Trail.

Over the remainder of the run — past Eagle Rock and through Garapito Canyon — the clouds continued to move overhead. A few drops of rain found me near the end of the run, but the most pleasant surprise occurred on the drive home, when showers dampened the  streets of the western San Fernando Valley.

There had been no rain in the Los Angeles area this October, and the showers reminded me of the erratic nature of Autumn precipitation in Los Angeles. Even though “normal” rainfall in October at Downtown Los Angeles (USC) is 0.66 inch, no one familiar with L.A. weather is surprised when October is dry. Over 143 years, Downtown Los Angeles has recorded no October rainfall 26 times, 0.10 inch or less 54 times, and 0.25 inch or less 74 times.

The upper-level low continued to influence the day’s weather, and while the low remained mostly offshore and didn’t generate any more showers in the West Valley, it did produce a colorful sunset!

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Warming Up for the ANFTR Trail Races

Stratus in the San Gabriel River drainage from Mt. Wilson road.

Was back on Mt. Wilson this morning, enjoying the mountains, and getting in a little more training for the upcoming Angeles National Forest Trail Run races.

There were already two cars parked in the loop road turnout when I got there, and another car pulled in behind me. All were runners.

The turnout is near the start of the ANFTR course and most of the runners were planning to do the ANFTR 25K loop or a variation. One runner — training for the ANFTR 60K and AC100 — was doing the 50K course.

The extensive layer of low clouds in the canyons of the West Fork and East Fork San Gabriel River at the start of the run was indicative of a cool onshore flow. Too cool and comfortable, really. Anticipating warmer temperatures for the ANFTR race, I wore an extra layer for the run, and probably should have worn more.

The last two years the ANFTR races have been run during record-setting heatwaves. We’ve had a lot of cool weather this year and for a while it looked like the pleasant weather might carry over to race day, July 6. But following the finest of ANFTR/Mt. Disappointment traditions, it now looks like temps will probably be warming up for the race. Maybe not quite as hot as the last two years, but still on the toasty side. We’ll see!

The highest temperature recorded at Clear Creek on the day of the ANFTR/Mt. Disappointment races for 2005-2019.
High at Clear Creek for the 2005-2019 ANFTR/Mt. Disappointment races. Click to enlarge.
Average hourly Clear Creek temperatures on the day of the ANFTR/Mt. Disappointment races for 2005-2019.
Average hourly Clear Creek temperatures for 2005-2019 ANFTR/Mt. Disappointment races. Click to enlarge.

Update Thursday, July 11, 2019. As it turned out, temperatures for the 2019 edition of the Angeles National Forest Trail Run were in the “middle of the pack” compared to other years. The high temperature recorded at the Clear Creek RAWS on July 6 was 80°F. This was down 25°F from 2018. Averaged hourly fuel temperatures at Clear Creek ranged from 101°F to 104°F between noon and 5:00 pm. The high at the Mt. Wilson RAWS on July 6 was 75°F, down 20°F from 2018.

Average hourly Clear Creek fuel temperatures on the day of the ANFTR/Mt. Disappointment races for 2005-2019.
Average hourly Clear Creek fuel temperatures for the 2005-2019 ANFTR/Mt. Disappointment races. Click to enlarge.

Note: The temperature in a commercial weather station is measured inside a white, ventilated instrument housing, several feet off the ground. Mid-day temperatures in the sun, in the summer, with a cloudless sky will be much warmer than this. Some stations, such as Clear Creek, also measure the fuel temperature — the temperature of a pine dowel in direct sun about a foot off the ground. According to the NWS (and common sense) exposure to full sunshine can increase heat index values by up to 15°F. In my experience the fuel temp gives a better indication of the actual temperature a runner can experience in the sun, especially on exposed mountain slopes facing the sun.

Update Monday, July 1, 2019. Last week the GFS weather model was forecasting temps on race day to be near 100 at the lower elevations and over 90 on Mt. Wilson. This morning’s GFS max temperature forecasts are down about 10 degrees from that. Basically highs in the low 90s (in the shade) for the lower elevations and around 80 at Mt. Wilson. Temps in the sun, especially on exposed sun-facing slopes, could still top 100. If the forecast holds, the temperatures today should be similar to those on race day. We’ll see! Here are links to the Clear Creek RAWS and Mt. Wilson RAWS.

Some related posts: ANFTR/Mt. Disappointment 2019, Another Scorching Angeles National Forest/Mt. Disappointment Trail Race, Record Heat for the 2017 Mt. Disappointment 50K & 25K

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Lasky Mesa: Dark Clouds and Sun

Dark Clouds and Sun. Photography by Gary Valle'.

From a run this May in Upper Las Virgenes Canyon Open Space Preserve (Ahmanson Ranch).

Normal rainfall for May at Downtown Los Angeles (USC) is 0.26 inch. This year Los Angeles recorded 0.81 inch in May, according to the NWS .

It was definitely wet and cool! Nineteen days were partly cloudy to cloudy. Ten days recorded at least a trace of rain. The average high was 70 degrees.

Oddly, during our recent drought, above normal May rainfall totals were recorded in 2011 (0.45 inch), 2013 (0.71 inch), and 2015 (0.93 inch). The most rainfall recorded in May at Los Angeles was 3.57 inches in 1921.

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Rainbow Colors in Cirrus Clouds Over Los Angeles

Circumhorizontal Arc Segment Over the San Fernando Valley, Near Los Angeles

Colors in the sky other than blue and white quickly catch the eye. This afternoon, just before driving over to Ahmanson for a run, I noticed a peculiar band of vivid spectral colors mixed in with a patchwork of high altitude cirrus clouds.

The bright band of color was in the wrong place to be a sundog, but because of its association with the cirrus clouds was likely some type of halo. Ice halos are formed by the refraction and reflection of light by the facets of an ice crystal, such as those found in cirrus.

When I got back from the run I checked online and found Les Cowley’s Atmospheric Optics web site. This site provides a wealth of info about ice halos and other optical atmospheric phenomena. The web site even makes available software to simulate various halos.

Circumhorizontal arc fragment over the San Fernando Valley, near Los Angeles, on May 29, 2019.
Circumhorizontal arc fragment over the San Fernando Valley, near Los Angeles, on May 29, 2019. Click for larger image.

The height of the sun above the horizon, the height of the band of color, and the prismatic sequence of the colors and their brightness all suggest the band is a segment of a circumhorizontal arc.

While not an everyday phenomenon, the circumhorizontal arc is more common at Los Angeles’ latitude than a higher latitude city such as Seattle or London. If 0 degrees is the horizon and 90 degrees is directly overhead, the circumhorizontal arc can only be seen when the sun is higher than about 58 degrees. When the photo above was taken, the sun was at 69 degrees.

The circumhorizontal arc is typically formed by hexagonal flat plate crystals oriented with their large flat faces horizontal. Rays of sunlight enter through one of the edge faces and then exit through the bottom face of the crystal.

Now that I know when and what to look for, I’ll be keeping an eye out for more ice halos.

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Running to Ray Miller

Mountain bikers enjoying the view of Boney Mountain from Overlook Fire Road in Pt. Mugu State Park.

The Ray Miller Trailhead in Pt. Mugu State Park marks the western end of the Backbone Trail, a 68-mile scenic trail along the spine of the Santa Monica Mountains. The Ray Miller Trail’s long, winding descent into La Jolla Canyon is a favorite of runners and hikers, and a fitting end to those traversing the BBT from east to west.

My run this morning was to the Ray Miller Trailhead (and back) from Satwiwa, starting at the Wendy Drive trailhead in Newbury Park. The Wendy Drive Trailhead is very popular and is the starting point for many good runs, hikes and rides. To get an idea of the route options, see the detailed trail maps on the Pt. Mugu State Park page of VenturaCountryTrails.org.

Today I was looking to do a longer run, so didn’t take the usual route. On the way down Big Sycamore Canyon, I skipped the turns at Wood Canyon (Hell Hill), Wood Canyon Vista Trail (BBT) and Fireline Trail and at Overlook Fire Road, some eight miles into the run, finally headed uphill.

View of the Pacific, Anacapa Island and Santa Cruz Island from the Ray Miller Trail
View of the Pacific, Anacapa Island and Santa Cruz Island from the Ray Miller Trail.

The top of the Ray Miller Trail is a stout 2.5 -mile climb from the bottom of Overlook Fire Road. Along the way there were excellent views of Sycamore Canyon, Serrano Valley and Boney Mountain.

About a half-mile down the Ray Miller Trail there is a popular overlook of the coast. The day was clear and there were stunning views of the Pacific and the Channel Islands. Brushed by whispers of wind, the cerulean blue Pacific filled my view for much of the descent to the parking lot.

It was an odd feeling to run down to the parking lot with runners who were cheerfully finishing their morning run, knowing that I had many more miles to go. After a quick stop at the water spigot, I turned, and sighed, and took the first steps back up the hill and toward Satwiwa.

Here are a few photos taken along the way.

Related post: Ray Miller Training Run

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Simi Valley Snow Shower

Simi Valley Snow Shower

There were many reports of snow, sleet, hail, and graupel around the area yesterday.

It was definitely cold! The afternoon temperature at 1700′ at the Cheeseboro RAWS was around 42°F. And the temperature was probably cooler in the vicinity of convective showers, such as the one above.

The photograph is from Sage Ranch, at an elevation of about 2000′. I was hoping to see some snow on the ground — but no cloud buildups cooperated.

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