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Trail Weather

Weather Forecasts and Current Conditions

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Riding after Rain

Most trails in our local riding area don't respond well to rain. They have a high content of clay that turns into sticky, slippery muck that binds to everything it touches. It builds up on the tires, like a snowball rolling downhill, until it jams on the frame and the wheels won't budge. Some models of clipless pedals refuse to yield when full of this mud, resulting in the bike and the attached rider lying sideways in a puddle.

Most wet trails don't respond well to bikers, hikers or equestrians until they've had time to dry out. Hikers and horses make holes and ridges in the trail that become as hard as concrete when the trail dries. These holes and ridges are good for twisting ankles of trail users who aren't constantly watching their step.

On wet trails, bikes make grooves down the middle. These grooves collect water when it rains again, turning first into little channels to move the water downhill, then into little ruts, then large ruts that destroy the trail. You've heard about the beat of a butterfly wing that causes a hurricane? Then remember the tire track that turns a tail into one large rut!

And the mud is particularly hard to remove. It sticks to the bike and shoes, no matter the efforts to remove it, rubbing off on the bike rack, car carpet and floor pedals. Once home, it takes the careful use of a garden hose to remove the mud but not force water into the sensitive parts of the bike.

For these reasons, riders are well advised to stay off the trails after a rain until they have dried. How long to stay off? That depends on a number of factors including the particular trail, how much rain it received, how much sun it gets after the rain (is it in the shade or face south?), how warm and windy the weather is, and so on. After an isolated light rain you can probably ride the next day. After a heavy rain, you should wait several days. This is something where common sense and experience will help.

But if the trails are soaking, all is not lost if you need to ride! There are a few trails that hold up well when wet because they have more sand and rock that doesn't hold the water. Here are a few you should know about:

  • Space Mountain (Los Robles West) to the picnic table is almost always rideable, even right after a big storm. However, it can be pretty mucky from the picnic table to Potrero Road.
  • Rosewood Trail is pretty good, but not quite as resiliant as Space Mountain.
  • Zuma Ridge Motorway
  • Dirt Mulholland around Topanga State Park.
  • Brown Mountain Fireroad
  • Most San Gabriel Mountains trails made up of decomposed granite
  • Beardry Fireroad
  • Hoestetter Fireroad
  • Mt. Lukens

Wind, Red Flag Warnings and Fire

Southern California is a fire-prone area characterized by an extended dry season and dense chaparral vegetation that dries out from spring through fall. Fire is a natural part of the Chaparral plant community life cycle, burning once every 30 years on average. Southern California experiences intense Santa Ana winds typically in the fall and into winter. Santa Ana’s originate over the desert at altitudes upwards of 3,000 feet and the air mass travels towards the coast at sea level. As the air travels down slope, it heats up and dries out. Combine these strong, hot, dry winds with dry, waxy vegetation, and we have extremely high fire potential.

In LA County, fire danger is assessed by measuring the moisture content of vegetation. When plant samples have a moisture content of less than 60%, fire danger is considered critical. This normally occurs in September, but when we have a winter with little rainfall, this can occur as early as June. Usually it is not until we have heavy winter rains that the danger abates.

Red Flag Days are determined by the level of fire danger being HIGH or EXTREME, combined with Red Flag weather criteria provided by the National Weather Service. The local Red Flag weather criteria are any one of the following:

  • Relative humidity of 15% or less with either sustained winds of 25mph or greater, or frequent gusts of 35mph or greater for six hours or more
  • Relative humidity of 10% or less for 10 hours or more
  • Widespread and/or significant dry lightning.

As mountain bikers, there are a few things that we need to be aware of.

  • On hot and windy days, check the news and weather reports for Red Flag warnings, or call State Parks at (805) 488-8147.
  • Avoid park areas that are closed, both for your personal safety and because if a fire breaks out, agencies may have to allocate their resources to evacuate you, rather than deploying those resources elsewhere.

Following a fire, trails may not be opened for weeks. According to the Mountains Recreation Conservation Authority (MRCA), several things need to occur before park areas are deemed safe to re-open. Agency personnel need to make sure the fire is completely out (tree trunks and roots can smolder for weeks) and that trail hazards are alleviated or removed. In addition, surviving animals need time to relocate without the additional stress of human intrusion. And, when the parks re-open, it is more important than ever to stay on established trails to allow for natural regeneration of the ecosystem to occur and to avoid causing erosion, especially with winter rains approaching.

As users of the backcountry, it is important for mountain bikers to act responsibly, not only when riding, but also by knowing when not to ride. Part of our continuing effort to gain access to more trails is demonstrating to both land managers and other users of the trails that we are responsible members of the trails community, and that we will treat the backcountry with the respect that is required to preserve it.






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