Was that thunder? I warily eyed the dark clouds over the mountains and pondered the situation.

I was about halfway to the top of the Chumash Trail and was planning to run along the crest to Rocky Peak. The run had started in short sleeves and sunshine, but it was pretty obvious that wasn’t going to last.

A cold upper-level low had brought badly needed rain to the area for the past two days. The low was moving off to the east, but there was still a chance of afternoon showers and maybe even a thunderstorm.

It was the “thunderstorm” part that I needed to pay attention to. I had enough gear to deal with a downpour and cooling temps, but electrical storms are no fun at all.

I decided to continue to the top of the Chumash Trail and reassess. As I worked up the trail, I pictured the counterclockwise circulation around the low, and how convective cells develop over the mountains and then dissipate as they drift south. The concern was that the cells don’t always dissipate.

It looked like things weren’t getting any better at the top of the Chumash Trail, but it wasn’t worse either. I hadn’t heard any thunder for a while, and most of the activity seemed to be a few miles to the west and east. Having been starved of stormy weather for much of the rain season, I turned right on Rocky Peak Road and headed south toward Rocky Peak.

The run from the Chumash Trailhead to Rocky Peak is a challenging mix of technical single-track trail and hilly fire road. There are wide-ranging views of Simi Valley & Simi Hills, the San Fernando Valley, Santa Monica Mountains, Ventura County mountains, and San Gabriel Mountains. On a clear day, the view can extend to the Channel Islands, Saddleback, and San Jacinto Peak.

The actual turnaround point for a run to “Rocky Peak” varies. Some like to turnaround at the high point of Rocky Peak Road that is near Rocky Peak. Most of the time, I turnaround at a viewpoint that is at the end of a spur trail that branches off from the high point of Rocky Peak Road. From time to time, it’s fun to hike over to Rocky Peak and scramble to the top. That’s a bit more involved and requires some route-finding.

I felt the first raindrops as I reached the high point on Rocky Peak Road and turned onto the spur trail that leads to the overlook. There was some increased development to the east, but it looked like there would be enough time to get over to Rocky Peak, take a couple of pics, and then head back.

I felt a little exposed on top of Rocky Peak. I hadn’t heard any thunder for the past hour, but a cell to the east was spouting heavy rain over the San Fernando Valley, which meant there was probably enough development to produce lightning. I took the title photo and a couple of others and hurriedly descended from the peak.

Back on Rock Peak Road, the sprinkles increased, and the showers became more steady as I ran north toward the Chumash Trail. Under the dark clouds, a raven perched on a large pinnacle cawed incessantly, either enjoying the rain or complaining about it. In the distance, a siren wailed down in the valley. It was cold, and I was very glad to have an extra shirt, sleeves, gloves and a light rain shell.

As I began the descent of the Chumash Trail, the sun briefly broke through the clouds, reflecting brightly on the wet sandstone rocks. I breathed deeply, relishing the smell of the cleansed air and wet chaparral, and continued down the trail.

Here’s an interactive 3D terrain view of my GPS track. Over the run, the temperature sensor on my pack recorded a drop of about 30 degrees — from around 70°F at the start of the run to about 40°F when the showers began! Here’s what a NOAA Radar Mosaic looked like at the start of the run and when I was on Rocky Peak.

Related: Chumash Trail, Rocky Peak, Thunderstorm