For this week's final blog post, I chose to write about a weather phenomenon I am fairly familiar with: thunderstorms. Although there are many dangerous weather hazards like icing and wind shear, this one seems to have a combination of most all weather hazards associated with it. Another reason I chose to write about thunderstorms is because I currently live in the southeastern U.S. and if you do too, you are probably familiar with the daily summer afternoon thunderstorms and how annoying and dangerous they can be.
There are three elements necessary for a thunderstorm to form (PHAK, 2016):
Moisture
Unstable air
An uplifting action
Let's talk about how pilots can use basic weather information to predict and determine if thunderstorms will develop. First, let's see how we can determine moisture content. The moisture present in the air can be visible, like rain and fog, but it does not have to be. One way to determine moisture content in the air would be to look at the temperature/dewpoint spread. Observations, like a METAR, report the current weather conditions at an airport and one of those conditions reported is the temperature and dewpoint. The dewpoint is the temperature the air has to be cooled to in order for the air to become 100% saturated (PHAK, 2016). When looking at the two values, the closer the temperature/dewpoint spread is, the more saturated the air will be and as the spread nears zero, you can expect visible moisture to develop.
The stability of the air is defined as its ability to resist vertical movement (PHAK, 2016). To determine whether or not the air is stable, a pilot can look at a winds and temps aloft chart. This chart displays the wind direction, speed, and temperature at different altitudes for different locations. The standard temperature lapse rate is a decrease of 2 degrees Celcius per 1000 feet (PHAK, 2016). When observing the temperature change in the winds and temps aloft, if the lapse rate is greater than and exceeds the standard lapse rate, the air is considered unstable.
There are many ways to create an uplifting action. The first factor a pilot can look for is fronts. A front is a boundary between two air masses and as a front passes through, it can cause winds to shift and air to be forced upward, essentially creating a lifting action (PHAK, 2016). To locate frontal activity, a pilot can use a surface analysis chart or prognostic charts (PHAK, 2016). Pilots can also use these charts to locate low-pressure systems. In an area of low pressure, the air rotates counterclockwise, inwards, and upwards, again creating an uplifting action (PHAK, 2016). Lastly, a pilot can analyze the terrain in which they are flying. As air travels over mountainous areas and through valleys, air can be forced upward creating an orographic lifting effect.
Along with what has already been discussed, there are other resources pilots can use to determine if thunderstorms will be present. One of the common weather advisories that are issued specifically for thunderstorms is Convective SIGMETS. These advisories are issued in the presence of convective activity and advise of conditions that can affect all aircraft, big or small (PHAK, 2016). They are issued pretty much for any weather associated with a thunderstorm to include surface winds greater than 50 knots, hail 3/4 of an inch or greater in diameter, squall lines, embedded thunderstorms, icing, tornadoes, etc. (PHAK, 2016). Pilots can receive these advisories in many ways including contacting an FSS weather briefer or through the use of the Aviation Weather Center online.
As we all know, thunderstorms are dangerous. Just about every bad weather hazard can be associated with a thunderstorm. Thunderstorms can cause (PHAK, 2016):
Severe turbulence
Windshear
Icing
Hail
Tornadoes
Heavy Precipitation
Reduced visibility
Lightning
What if your flying and get caught in or around a thunderstorm?
Advisory Circular AC-00-45C lists out the do's and dont's when flying in and around thunderstorms (FAA, 2013). If flying near a thunderstorm there a many things you can do. To list a few, a pilot should maintain a distance of 20 miles from a storm, should never fly underneath an anvil or underneath of thunderstorm, should never takeoff into an approaching thunderstorm, and should deviate as necessary to circumnavigate it (FAA, 2013). If a pilot penetrates a storm, a few things recommended it to maitain the aircraft attitude, set the power for manuevering speed, turn on pitot and carb heat, dont turn around, and keep eyes on the instruments (FAA, 2013).
To close this blog post, I will post a video dicussing the hazards of thunderstorms. In this video by MzeroA Flight Training, an accident report was analyzed talking about an inflight aircraft seperation incident due to thunderstorm penetration (2020).
Federal Aviation Administration (FAA). (2013). Advisor Circular 00-24C, Thunderstorms. Retrieved from https://www.faa.gov/documentlibrary/media/advisory_circular/ac%2000-24c.pdf
Federal Aviation Administration (FAA).
(2016). Pilot’s Handbook of Aeronautical Knowledge (PHAK). Retrieved https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/
MzeroA Flight Training. (2020, April 7). Understanding the Dangers of Thunderstorms- MzeroA Flight Training [Video]. YouTube. https://www.youtube.com/watch?v=W4lg1y-ooz8
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