We are in the dog days of summer, which of course means the regular appearance of afternoon thunderstorms. Remember that three things are needed to form a thunderstorm: moist air, atmospheric instability, and a lifting force. Being that our slender peninsula is approximately 110 miles wide at our latitude, surrounded by the warm waters of the Gulf of Mexico and the Atlantic ocean, we enjoy a constant premium on humid air! Thanks to uneven heating across our landmass, lakes, and coasts, and the warm midday sun providing the lifting action, we have the perfect ingredients for thunderstorms on a daily basis. The Canadian Geographic has a succinct explanation of thunderstorms:
"Thunderstorms begin when a parcel of warm, moist air begins to rise. As the air expands and cools, the water vapour within it condenses and forms a cloud (When air masses collide). If there is sufficient atmospheric instability, the heat released by condensation will keep the air inside the cloud warmer than the air surrounding it, enabling it to grow larger and higher. The power of the rising air, or updraft, keeps millions of water droplets in suspension until they become so heavy they fall as rain."
Of course, the rain falls back through the column of rising air, causing friction, which leads to a charge of static electricity. Eventually the electrical buildup discharges in the form of lightning. Interestingly, a thunderstorm cannot be classified as such until the first lightning strike is observed. Until that point in time, it is just a large, heavy rainstorm with associated wind gusts, hail, and severe updrafts/downdrafts.
These storms are common in Central Florida and most often appear as "air mass" thunderstorms. Classifying them as such may annoy meteorologists who believe that thunderstorms are always formed based on non-random factors. But, as pilots, what matters most to us is being able to determine whether the convective activity is the result of a frontal system, which could push a line of storms through the area as a squall line, or whether they are isolated cells "popping up" as the day wears on. A quick glance at the latest surface surface analysis and 12/24 hour forecast should provide a great deal of insight.
When air mass thunderstorms are present, what can we do? We can always choose to stay on the ground. This is the most conservative course of action. But when the cells are clearly isolated, skies are clear above, visibility and weather are otherwise acceptable, and the forecast calls for continued good weather at your home or destination airport, it is possible to launch safely and remain clear. Here are some flying tips.
- Always maintain a wide berth from thunderstorms. The FAA recommends you remain at least 20nm clear.
- Fly tactically. It's generally considered wiser to fly upwind of a thunderstorm, i.e. opposite its direction of movement. The worst weather will be just ahead of the thunderstorm. Usually, you'll find beautifully calm and clear weather in the wake of a thunderstorm.
- If you are trying to get ahead (downwind) of a thunderstorm, stay well clear of its boundary. Sometimes this is the best course of action if you can position yourself well ahead of the storm; this may allow you to arrive at your destination prior to the storm's arrival. However, be sure to leave yourself plenty of time to land, tie down, and get inside before the first signs of convective activity arrive at the airport. If you're not certain you'll make it in safely, it's always best to land and wait for the storm to pass. Thunderstorms usually "live" for only 30-60 minutes, so your delay will most often be a short one.
- Take advantage of ATC, stormscope, datalink weather, weather radar, or any other tools you may have in the cockpit. But be warned: ATC does not guarantee smooth rides or safe passage with weather avoidance vectors! You are the PIC. If your Mark I eyeballs disagree with the controller, trust your instincts.
- Use Flight Watch (122.0MHz) to stay in tune with the latest weather.
- When low, stay away from visible rain columns.
- Manage your fuel carefully when deviating at low altitudes.
Ryan Ferguson is a CFI/I and MEI for the CAP Flying Club. He can be reached via email at ryan@hawkerpro.com or (407) 920-7660.