Late every summer in Zion National Park, monsoon season hits. It brings torrential downpours that soak the park in a matter of minutes. A rainstorm can bring some relief from the desert heat. However, it can also turn a fun hike deadly in a matter of minutes.
Flash floods are a serious, frequent threat throughout the region. Occurring with little or no notice, and sometimes starting miles and miles away from the nearest downpour, they catch even seasoned hikers by surprise.
What Causes Flash Floods?
Flash floods are a far cry from normal flooding. Rather than growing gradually over a matter of hours, days, or even weeks, flash floods can start with little to no warning. No prior flooding or high water levels need to have occurred for a flash flood to start.
Typically, flash floods are caused by slow moving thunderstorms. These storms linger over an area, a little like a hurricane that lingers on land after coming ashore. Because they don’t move on quickly like normal storms, rain that would usually be spread over a great distance falls on a smaller, concentrated area. The ground is unable to soak up this increased rain fast enough, and it pools and runs downstream or downhill.
Another way that flash floods can occur is when snow and ice melts. When sudden warm days melt large amounts of snow and ice quickly, the ground becomes saturated and can’t soak up any more moisture. The water has to go somewhere, and that somewhere is downhill into low-lying areas.
Where Do Flash Floods Occur?
Flash floods can occur on any flat ground. But they usually happen in low-lying areas, because that is where the water goes first during a downpour. Dry riverbeds, small streams, and canyons are particularly susceptible.
Among the most dangerous spots to get caught during a flash flood is a slot canyon. The high walls of these narrow canyons make it difficult to get away as water rushes through them.
Not all flash floods occur in areas that are usually dry. Rivers and creeks may also experience flash floods, as large amounts of water cause current river or creek levels to rise rapidly.
The Earliest Warning Signs
While flash floods are by definition largely unexpected, they aren’t entirely without warning signs. During a rainstorm, large puddles forming can indicate that the ground is too saturated to hold any more water, which can mean that flooding is likely. If you are near a river or creek, watch for an increase in debris traveling downstream. The water may also become muddy and churning, or visibly pick up in pace.
If you notice any of these signs of flooding, it’s always best to seek higher ground. If you are in a slot canyon and it begins to rain, even if it isn’t heavy, get out as soon as you can to avoid getting caught in a place that you can’t get out of during a flash flood.
Tips to Stay Safe from Flash Floods
Simply watching for the early warning signs of a flash flood isn’t enough to keep yourself safe. Instead, it’s important to be proactive.
Check the weather ahead of your trip, and then during your vacation. Before you start hiking for the day, you’ll want to not only check the local weather report, but also stop by or call in to the visitors center to find out what Zion’s current flash flood rating is. This rating system is designed to give hikers a better idea of the day’s threat of rain, and with it, flash floods. The four flood ratings include:
Expected: This is the highest possible flood risk. When this warning is present, stay away from slot canyons, dry creek beds, and other areas that are prone to flooding. Flooding may also be a risk in areas that aren’t usually prone to flash floods when this rating is present.
Probable: This flood rating means that flash floods are likely in certain areas of the park. This includes dry creek and river beds, canyons, etc.
Possible: Flooding may not be expected when this rating is present. But rain in the area or distant area mean that flash floods could still occur. Be aware of changing weather conditions and check back often to see if the risk increases later in the day.
No Expected: While flash flooding can still occur when this rating is posted, this indicates the least risk of flash floods. Again, conditions can change throughout the day, so it is always important to check back before starting a hike in a flood-prone area.
Staying Safe in Zion National Park
Flash floods are a serious threat during monsoon season. But this doesn’t mean that you can’t enjoy a visit to Zion late in the summer. Being aware of the weather and the park’s flood rating, as well as knowing the signs to watch for, can help you stay safe on the trails all year long! And on days when rain keeps you off of the trails, check out these 7 other things you can do in Zion besides hiking.