The weather has calmed in Southern California. Medium range models are forecasting a break of about a week in what has turned out to be a very busy rain season. Over the last 90 days a precipitation pattern typical of El Niño has emerged in the western U.S. This is reflected in rainfall total for Downtown Los Angeles (USC), which is now at 13.2 inches for the water year -- 4.78 inches above normal.

The dry weather could not have come at a better time for those affected, or threatened, by mudslides and debris flows. This small slump along a road at Ahmanson Ranch is indicative of the instability that can develop when soil becomes saturated. Had our recent wet pattern been more persistent, mudslides and debris flows might have been much more widespread and devastating.

One of about a dozen vernal pools in the Rocky Peak area. More than just a puddle, these rainy season pools form as a result of the area's unique geology.

In my experience, excessive rainfall is not necessary for the pools to form. Normal month-to-month seasonal precipitation is usually sufficient. Their persistence depends on several factors, but in a season with normal to above average precipitation, the pools can last for several months.

From Wednesday's run on Rocky Peak.

Related post: Vernal Pool at China Flat

Computer models and other tools continue to forecast a shift to an "El Nino like" upper flow pattern next week that could result in an extended period of wet weather in Southern California. I'll be updating Southern California Weather Notes on Wednesday with additional info.

The photograph of patterned altocumulus clouds is from this afternoon's trail run along the northern boundary of Ahmanson Ranch, near Los Angeles.

Following the little bit of wet weather we had at the end of the year, Southern California has been enjoying idyllic weather with highs in the 70's and 80's. Southland cities recorded the highest temperature in the continental U.S. several days this week. Tuesday San Diego recorded a high of 84 degrees, tying Kalaeloa, Hawaii for the warmest temperature in the nation.

The weather's been great for trail running -- and for the chaparral plants. Alternating periods of wet weather and warm weather have encouraged growth and flowering, and I've been seeing a number of rainy season wildflowers. In addition to the milkmaids in the photograph above, some of the early bloomers include nightshade, peony, shooting star, woolly blue curls, prickly phlox, chaparral mallow, rattlesnake weed, and several others.

Rainfall totals in Southern California this rain season to date have generally ranged from an inch or so above normal to an inch or so below (WRCC). As of yesterday, Downtown Los Angeles (USC) precipitation was 0.56 inch above the norm for the water year to date. Although January has been dry so far, it looks like we may see a shift to more seasonable -- and wetter -- weather around midweek next week.

The precipitation pattern we've seen on the West Coast so far this rain season has a bit of an El Nino flavor to it, and that pattern may become better defined in the coming weeks. Today's 6-10 day and 8-14 day precipitation outlooks from the Climate Prediction Center indicate above average rainfall for Southern California. We'll see!

Got caught in some showers this afternoon on Rocky Peak, returning from a rambling trail run from the San Fernando Valley over into Simi Valley.

This was one of those "not sure where I'm going" runs that unfolded as it progressed. It started near Chatsworth Reservoir at Chatsworth Oaks Park, worked over to Santa Susana State Historic Park, then up the Old Stagecoach Road. At the top of the old Stagecoach Road, I picked up the Upper Stagecoach Trail and followed that to Santa Susana Pass and the 118 Frwy. From there it was a short distance down the west side of Santa Susana Pass Rd. to the Lower Stagecoach Trail, which took me to Corriganville.

Once down in Simi Valley there are four trails that ascend to Rocky Peak road, and my return route. From the shortest to the longest, they are the Wildlife Corridor trail, Hummingbird Trail, Chumash Trail and the Marrland/Las Llajas trail. Not sure how long it would take to get back to the SFV, I finally decided on the Chumash Trail.

Running up the Chumash Trail, the wind picked up, the clouds began to lower and thicken, and the temperature dropped. Minutes after turning right onto Rocky Peak road the showers began, and it wasn't long before the sleeves came out of the pack.

The return trip, with a net elevation loss, went a little quicker than expected. Next time I'll have to give the Las Llajas option a try. That would extend the run from about 17 miles, to something over 20. The approximate elevation gain/loss on the 17 mile version was a little under 3000 ft.

Related post: Old Santa Susana Stage Road

Some outstanding evening runs this week. Did a FiveFingers run out at Ahmanson on Tuesday, and as sometimes happens this time of year, didn't make it back before dark. Was up on Lasky Mesa in the fading light, with endorphins at full flow. In a distant grove oaks I could hear a Great Horned Owl, and with each hoot-whoo it seemed the zeal of the day was turning to the tranquility of the night. The running was effortless and ethereal.

This evening's run was also superb. Over the course of the run, the skies had become increasingly gray and troubled, as a weak cold front approached the area. Climbing a long hill, the light was dank, and I had given up on the sun. But as I neared the crest of the hill, orange-red sunlight began to illuminate the clouds from below, highlighting a sunset shower. Large, cold rain drops began to patter around me, and I watched mesmerized, as the light, clouds, and rain played on the sky.

The first day of sun following rain on Tuesday and Wednesday. Ahmanson Ranch was not nearly as wet and muddy as I expected, and although water was pooled in Las Virgenes Creek, the stream was not running. Would have been a very different scenario had this storm occurred later in the rain season. Some rain totals for the Los Angeles area and comments about the developing El Nino are in my October Weathernotes.

The soft trail conditions were nearly ideal for barefoot running, and I took my running shoes off part way through the run. The muddy sections were great fun, and running barefoot was a enjoyable way to put a wrap on the rain event. I can't wait for it to rain again!

The grass backlit by the sun is smilo (Piptatherum miliaceum). Introduced into California over a century ago, smilo is a drought resistant grass that has been used for pasture, and for erosion control following fires.

Clouds swirled around me as I worked up the steep trail toward an overlook near Rocky Peak. I stopped and listened to the patter of the rain against the rocks, its intensity rising and falling with the gusts of wind.

The wind-driven rain trickled down my face, tasting cool and clean. It didn't matter that my running clothes were soaked and that with each gust I could feel a chill. It was raining!

In the same manner that a color will sometimes appear especially pure and vibrant, there was an unusual liveliness to this rain.

Who would think a western Pacific typhoon could so directly affect California's weather? But that's what is happening. The moisture from typhoon Melor, which was over Japan just a few days ago, was captured by an extending and strengthening jet stream. This has resulted in an atmospheric river of moisture, stretching across the Pacific and into California.

This morning, Intellicast composite radar shows Northern and Central California already being hammered by the system. Southern California has seen a few showers, and several stations have already recorded significant rainfall. As of 9:00 a.m. the CNRFC Precipitation Map shows isolated 24 hr. rainfall amounts in the foothills and mountains of Santa Barbara, Ventura, and Los Angeles County ranging from about 0.16 inch at Sandberg to 0.61 inch at West Big Pine.

The last day there was measurable rainfall at Downtown Los Angeles (USC) was on June 5, 2009, when 0.13 inch was recorded. Computer weather models forecast the best dynamics and highest rainfall totals will be in the northern two-thirds of the state, but in recent days have been trending wetter in the Los Angeles area, particularly in the mountains.

With so much moisture in the atmosphere, it takes very little lift to produce rain. Onshore winds, full of moisture, are lifted by foothills and mountains across the flow, and the result is rain -- sometimes lots of it. In this case it appears the south to west facing mountains and foothills of Santa Barbara, Ventura and Los Angeles counties may record much higher rainfall totals than the lowland areas.

In a decade characterized by unusual El Ninos, the ongoing El Niño of 2009-2010 is another strange one. El Niño signals continue mixed. The Aug-Sep Multivariate ENSO Index (MEI), decreased from 0.978 to 0.754, however other El Niño signals appear to be rebounding. In the last two weeks low level equatorial westerly anomalies have increased significantly. The reduction in the strength of the trade winds, and a downwelling Kelvin wave resulting from a very strong westerly wind burst already appear to be increasing upper ocean heat content in the central equatorial Pacific. The 30 day moving Southern Oscillation Index (SOI) has been dropping, and should return to negative territory in a day or so.

Recurring equatorial westerly wind bursts and enhanced west-central Pacific convection has been slowly migrating eastward. The most recent round of enhanced convection was centered at about 160E. This is consistent with a developing El Niño, and may have contributed to the creation of the atmospheric river now affecting California, by helping to extend the Pacific jet stream following an East Asian mountain torque event.

However, total and relative AAM remain negative, and are lower than is generally the case during a developing El Niño. Of the weak to moderate El Ninos that have occurred Since 1959, only the 1977-78 and 1994-95 El Niños have had negative average July-September relative AAM values comparable to the current El Niño. Since 1959, only 4 of 15 El Niños have had negative average relative AAM values during the Southern California rain season of November to March. (Revised 12/14/09)

Moderate El Niños come in many flavors and have varying impacts. Under the guise of such El Niños Los Angeles experienced its second wettest water year on record in 2004-2005, when 37.25 inches of rain was recorded; then in 2006-2007 had its driest water year on record, when only 3.21" was recorded. What flavor will the 2009-2010 El Niño be?

The photo of the tree and clouds is from yesterday's run at Ahmanson Ranch.

Related post: How Does the El Nino of 2009-10 Compare to Other Warm ENSO Episodes Since 1950?

The windward side of this foxtail pine snag has been blasted by the icy winds of a multitude of Winter storms. The wind has sculpted the mineral-like wood, exposing and accentuating its inner layers.

The photo is from last Saturday's Cottonwood Pass - New Army Pass trail run. Nearly all of this route is above 10,000 ft. and 12 miles of it are above 11,000 ft. This relatively dry, high altitude habitat is home to the southern foxtail pine (Pinus balfouriana subsp. austrina).

One of the less common Sierra conifers, the tree is a long-lived species that is closely related to the bristlecone pine. The FEIS database references a southern foxtail pine 3400 years old, and the Gymnosperm Database a specimen with a crossdated age of 2110 years.

Because the tree grows so slowly, the wood is dense, and dead trees are slow to decay. In the vicinity of Cirque Peak, and a few other areas, dead foxtail pines and remnants are found above the current tree line. By crossdating tree ring sequences, a study published in 1997 found that over the past 3500 years the tree line in this part of the Sierra has generally been higher than it is now.

The study deduced that one period of reduced tree abundance and lowered tree line elevation was associated with warmer temperatures, and at least two severe multi-decade droughts. In contrast, the most recent decline has occurred during a cold, wet period that started about 450 BP.

It is remarkable that some of the dead foxtail pines studied here were alive during the Bronze Age, 4000 years BP.

Or should that be ramping UP for Mt. Disappointment? Anyway, started tapering for the Mt. Disappointment run next Saturday. Did the 13 mile Cheeseboro Canyon keyhole loop from the Victory Trailhead of Ahmanson Ranch yesterday, and then stretched the legs at Sage Ranch today. Both mornings were cool, with low clouds and fog -- very pleasant!

Here's hoping for "not too hot" weather for the race. At the moment, the GFS and ECMWF weather models show a weak upper level trough moving through California in the Friday-Saturday timeframe. Such a scenario should increase the chances of "seasonable" temps for the race -- which would still be quite warm, but maybe not crazy hot.

Update Friday Morning 8/07/09. Broad upper level trough over California this morning is keeping things cool. Yesterday the high recorded at Mt. Wilson was 70, and the low overnight was 48! Southern part of the trough is forecast to hang back over Southern California through Saturday, which could result in temps a little BELOW normal for the Mt. Disappointment race. We'll see!

Related post: Mt. Disappointment 50K 2008 Notes

Poison Oak Along the Blue Canyon Trail.

Since nearly all my weekday runs are in the afternoon, on Summer weekends I usually like to escape the heat and do a run in the mountains -- the higher, the better. But today even the mountains were going to be hot. Hot enough that the National Weather Service had issued an Excessive Heat Warning for a combination of heat and humidity that would "create a dangerous situation in which heat illnesses are likely."

It would be cooler at the higher elevations of the Sierra, but there was good chance of thunderstorms developing along the crest of the Sierra, as well as most of the higher mountains of Southern California. Considering the options, I finally decided to do an early morning run in Pt. Mugu State Park. If I was going to run in the heat, it might as well be a scenic run close to home. Maybe the weather in the mountains would be better next weekend.