…Thunderstorms and Severe Weather in California ...

Thunderstorms affect relatively small areas when compared with hurricanes and winter storms and many are beneficial, bringing needed rainfall to an area. But while only a fraction of these storms are classified as severe, ALL thunderstorms are dangerous! Thunderstorms produce lightning and strong winds and often also bring hail, tornadoes, and flash flooding. An average of 300 deaths and more than 2000 injuries a year are attributed to thunderstorms and the associated affects. These dangers exist in every region of the United States …even in California !

Thunderstorms occur in every part of California and in every month. It is common for thunderstorms to develop along the Sierra Nevada Mountains in the late summer and early autumn months…but it is just as typical for thunderstorms to move through Southern California in the winter. And just as in the Midwestern states, most locations can expect to see thunderstorm activity in the springtime.

What is different about California thunderstorms is that they tend to be more locally focused rather than developing into large storm complexes that sweep through several states in a day. The result is that most people outside of the impacted area are unaware of what has occurred and unless their area is directly hit by a storm the resulting impression is that severe weather does not occur in our state. But Californians need to be prepared for all forms of severe weather.

There are five significant severe weather hazards produced by thunderstorms. These are lightning, strong winds, hail, flash flooding, and tornadoes.

Lightning

Lightning occurs with all thunderstorms and kills more people than hurricanes or tornadoes! On average, someone is struck by lightning every day. Most of them survive but many do not. In the United States , lightning causes an average of 80 deaths and 300 injuries per year and many of these injuries occur every year in California .

The most important thing to remember about lightning is that it takes the shortest and most effective path it can find to the ground. It will likely strike the tallest object and/or one made of metal or near water in order to discharge into the ground. Therefore, if you find yourself on a hill, an open field, or on the water you are most at risk of being struck by lightning. If you are indoors, stay out of the bathtub and away from metal pipes and electrical wiring!

Another important thing to know about lightning is that it can strike the ground as much as ten miles away from the thunderstorm. If you see a thunderstorm anywhere near your location…not just overhead…you need to take precautions against being struck.

Strong Winds

Strong thunderstorm winds can exceed 100 mile per hour and can cause damage equal to that of a tornado. In fact, people are often surprised to learn that damage they think was caused by a tornado was instead caused by the thunderstorm winds. All thunderstorms can cause damage! Typical damage from these winds include large tree branches dropped onto vehicles and homes, sections of property line fences blown down, and gazebos and carport covers lifted and tossed.

Thunderstorm Microburst Wind Damage - Los Angeles County - 2000

Californians can reduce the potential for thunderstorm wind damage by keeping their trees pruned, properly maintaining fencing and external structures, and by putting lawn chairs and other mobile objects in the garage or shed when thunderstorms are in the forecast.

Hail

Hail causes more than one billion dollars in crop and property damage each year. There is not much that can be done to protect most property from these effects other than to move vehicles under cover when thunderstorms are forecast. However, many injuries and some deaths are caused each year in California when hail is encountered by drivers on the road.

Arcadia, Los Angeles County 2005

If you are on the road when a thunderstorm with hail moves through the area, pull off the road at the earliest opportunity and wait for the storm to pass. Most thunderstorms in California are small enough that it will only take a few minutes for the storm to pass by. The road surface may still be very slick and hazardous so extra caution is needed when returning to the road. However, it can be very dangerous to try to handle the slick driving conditions while the hail is also pelting your vehicle so don’t do both! And remember…the other drivers are encountering the same poor conditions and may not be handling it as well.

Flash Flooding

Flash flooding is the number one cause of deaths associated with thunderstorms. More than 140 people die every year because they are either caught by a sudden surge of water across the roadway or because they make the often deadly decision to drive through an already flooded crossing. Don’t do it!!

Flash Flooding in Ventura County 2005

Most deaths occur when people drive across flooded roads in their neighborhoods or other familiar areas. They believe the water is not too deep or that their truck or SUV is heavy enough to get them through the flowing water. What they don’t know is that the road surface is often washed away and the water is deeper and faster than it looks. And once a vehicle…any vehicle…is caught up by the water all control of the situation is lost.

Never drive across flooded roadways! Be very careful when driving or camping in the many mountains and foothills of California that you are not crossing or camping in a dry river bed. A thunderstorm that is miles away might be sending several feet of water through the same canyon you are in. Stay extra alert if thunderstorms are in the forecast!

Tornadoes

Most Californians don’t think tornadoes occur in our state. But in the past ten years alone there have been 113 confirmed tornadoes and almost three hundred funnel clouds from all regions of the state…an average of more than eleven tornadoes each and every year. In 2005, there were 30 confirmed tornadoes in California !

Twister in Rosamond, California

Nationally, there is an annual average of 70 deaths and 1500 injuries from tornadoes. Though there are no recorded deaths in California , tornadoes have caused significant damage to homes and other property. In many cases the winds from confirmed tornadoes have been estimated well in excess of 100 miles an hour. The result has been damaged rooftops and siding, broken windows, downed trees, and dangerous flying projectiles. We have been fortunate not to have had anyone in the wrong place at the wrong time!

If a tornado warning is issued for your area…take immediate action! Take cover in your bathroom or a small interior room such as a closet. Stay away from windows. Don’t try to drive out of the area as it is very dangerous to be in your vehicle when a tornado hits. Any time there are thunderstorms in the forecast, be thinking about what you would do if a thunderstorm were to produce a tornado in your area. Thinking ahead about which building or room is the safest will save precious seconds.

Before Severe Weather Strikes

- Have a plan. Discuss with your family and friends what to do when thunderstorms are in the forecast and there is a potential for severe weather. Planning should include identifying a safe place to take shelter in your home, office, and other locations.

- Have a NOAA Weather Radio with a warning alarm tone and battery back-up. This will help keep you informed about developing severe weather conditions and can be used regularly when planning outdoor activities.

- Know the counties in which you live and work and those nearby. Severe weather warnings typically refer to counties that are at risk and it is important to know which of these warnings are referring to your area.

- Regularly practice your plan. This is especially important if you have people in your house who are elderly, very young, or physically or mentally challenged.

- Know the weather forecast. The weather can change rapidly and conditions can deteriorate quickly. In most cases, preventative actions can be taken well in advance of a storm if you are aware that thunderstorms are in the forecast. For the latest weather forecasts, visit the National Weather Service at http://www.weather.gov or listen to NOAA Weather Radio for updated weather information or conditions.