In the summer months a good portion of our precipitation here in Jackson Hole, and throughout most of the Mountain West will be produced by thunderstorms. So, to help you avoid being caught out in a thunderstorm, and its associated lightning, I’ll give you a few hints on what to watch for in the sky, along with a few simple weather products to consult each day.
Typical Thunderstorms
Even on those days that begin with clear blue skies, puffy cumulus clouds can appear in the afternoon. These are caused by convection, or the afternoon heating of the ground that causes air to rise. Heating the ground causes the atmosphere to become unstable.
As the air rises higher into the atmosphere, it cools. Whatever moisture that is contained in the atmosphere, in the form of invisible water vapor, is then condensed into water droplets, water droplets coalesce together to form clouds.
If there is enough moisture and instability in the atmosphere, then those harmless, puffy, cotton ball-looking clouds might appear around noontime. By mid to late afternoon, they may grow into full-blown thunderstorms. If there is not enough moisture or instability in the atmosphere, then all we’ll see are harmless puffy clouds.
Clouds that Grow and Gather
Here are a few things to watch for to determine if those puffy clouds are going to develop into thunderstorms:
1) The first puffs of cumulus appear before noontime.
2) Cumulus clouds growing taller and begin gathering together.
3) The bases of the clouds get progressively darker, an indication that the clouds are growing taller.
4) The taller the cloud, the darker the bases, and the larger the area that the cumulus clouds cover, and thus the greater the potential for thunderstorms.
That is the progression of typical afternoon thunderstorms. However, thunderstorms do not only develop during the afternoon hours, there will be plenty of days that don’t fit this more typical pattern.
Untypical Thunderstorms
Storm systems, otherwise known as low-pressure systems, periodically roll across the Rockies during the summer months. Storm systems not only bring additional moisture and instability, but they also provide extra lift to the atmosphere, giving an extra boost to the vertical motion that allows thunderstorms to blossom.
Cold fronts are usually associated with low-pressure systems. Cold fronts are very efficient at providing extra lift in the atmosphere. When a cold front is passing through, more intense thunderstorms are always likely.
The last thing to be on the lookout for, is the summer monsoon. The Desert Southwest Monsoon is a seasonal wind flow pattern that brings very moist and unstable air up from central Mexico to the Four-Corners Region. Periodically, some of that moisture reaches as far north as Northwest Wyoming.
The important point to make here is, a low-pressure system, a cold front passing through, or monsoon moisture are each capable of generating thunderstorms at any time of the day or night.
Check the Forecast and Maps
Check the forecast each day to see if there is any mention of thunderstorms, even a small probability, like a 20-percent chance can be significant. A thunderstorm automatically implies the potential for lightning and may also portend a potential for heavy downpours of rain, or hail, or strong gusty winds. Also check the daily forecast weather map to see if there are any fronts nearby.
There are two other tools you can use for short term forecasting, to see if there is any lightning occurring nearby or upstream of your location. One is a Lightning Strike Map, the other is the GeoColor Satellite image with lightning flashes. Both products are available on the Satellite and Radar page of mountainweather.com
Keeping an eye out for developing thunderstorms is the first step to staying safe in the outdoors this summer. Nest we’ll look at some lightning safety tips and what you can do to reduce your chances of getting zapped if you do get caught out in a thunderstorm.
Lightning Safety
It’s always a crapshoot trying to forecast precisely when and where lightning will strike. Here I’ll share some facts about lightning and how to evade getting zapped in case you do find yourself unable to get to a completely safe location.
First thing is, most of the lightning that occurs with a thunderstorm stays in the cloud. About 75% of all lightning occurs within the cloud, only 25% of lightning produced in a thunderstorm with strike the ground. But those intra-cloud lightning flashes are a good indicator that ground strikes may be eminent.
How Lightning Can Hurt You
A single lightning bolt generates up to around 100 million volts of electricity, for a split second. During that split second, the temperature of a lightning bolt can reach 54,000-degrees Fahrenheit, which is about five times hotter than the temperature of the sun. There are a several ways that the electrical energy and heat from lightning can hurt you.
First, is being hit by a “Direct Strike”. The odds of this are very small, however, if you were unlucky enough to take a direct hit, it would be game-over, right then and there.
Second, would be through “Conduction”. Electrical energy travels through all metal objects, but also through graphite, carbon-fiber, and water. During electrical storms you should avoid direct contact with wire or chain-link fences, your fishing pole, hiking poles, tent poles, your bicycle or boat. Think of sticking your finger in a light socket, multiplied by about one-million times.
The third method by which lighting can hurt you is from what is known as “Side-flash”. The heat & electrical current that emanates outward through the air from a nearby lightning strike is intense enough to can cause cardiac arrest, concussive injuries, severe burns, and/or nerve damage.
Lastly, and the most common way of being hurt by lightning, is through “Ground Currents”. When lightning strikes the ground, the electrical current is carried outward, radially, in all directions through the ground. If that current reaches you it can travel up through your body, doing damage to vital organs. Cardiac arrest, burns, and severe nerve damage are also possible via ground current.
Direct strikes and conduction account for about 20-percent of all lightning casualties. Side-flash accounts for about 30-percent of injuries and fatalities. Ground currents alone account for the other 50-percent of all lightning injuries and fatalities.
Safe Havens from Lightning
The safest place to be during a thunderstorm is in a building or a car. A “building” means a 4-walled structure with a foundation and grounded electrical and plumbing. A picnic shelter or large tent may keep you out of the rain, but your lightning exposure is the same as standing out in the open.
A vehicle is the next best safe have. Contrary to what you might think, it is not the tires on your car that insulate you from te electrical current, it is the metal frame and body of the car that dissipate the electrical energy around you. A motorcycle or bicycle do not offer this same “halo” of protection.
If there is not a building or car to retreat to, get to lower ground. Get off any ridgetops. A study done in Colorado showed that lightning strikes the ridgetops 7 times more often than adjacent valleys.
You should also get off the water if you are on a lake or river. If you can, get to a grove of trees that are of similar height to wait it out. Do not run for the biggest, lone tree to get out of the rain. As soon as you can see lightning or hear thunder, you should be looking to seek shelter immediately.
There is not much we can do to protect ourselves from a direct hit or a side-flash. Conduction is something we can protect ourselves from, by not being in contact with any objects that can conduct electricity, including water. Be aware, that even other people can conduct electricity, like when standing in a crowd.
Don’t Huddle-up
Lightning that strikes nearby will generate intense heat and electricity. Think of a lightning bolt like a hand grenade. The standard U.S. Army grenade has a kill radius of around 25 feet and a casualty (injury) radius of roughly 50-feet. A group of people, standing close together, will result in more casualties.
Sheep & cattle often die in large groups after a single lightning bolt hits nearby because they group together. Sometimes, lining up along a wire fence.
When lightning is present, don’t huddle together. Instead, spread out 25 to 50 feet apart. That way, if someone does go down after the explosion, others in the group can give aid.
If you find yourself outside with no good place to hide when lightning is visibly nearby, then you can reduce your chances of injury from ground current by just standing still with both feet together. The current that travels through the ground will take the path of least resistance and can go up one leg, through your body and exit out the other leg. By keeping your feet together, you might take a bump from the ground current, but your vital organs will be spared, hopefully.
Sitting Indian style on the ground with your legs crossed is also acceptable. Lying down, like in a tent for instance, is not acceptable, as too many different parts of your body are contacting the ground. And by the way, that camp pad does not insulate you from ground currents.
In Summary, if you can’t, “Get indoors when thunder roars”, as the National Weather Service slogan says, then:
1) Get to the best un-exposed location you can.
2) Get away from any metal objects.
3) Spread everyone in your group at least 25 feet apart.
4) Stand with both feet together and wait it out.
Post by meteorologist Jim Woodmencey