Continue, Deviate, or Divert?

In some cases, it will be possible to continue on your current course and slow to maximum turbulent air penetration speed. In many cases you will need to alter your course to deviate around weather hazards, and in other cases the only alternative will be to divert to another destination. The squall line shown in Figure 34 may appear to have inviting holes in the line, but by the time you arrive at an opening it may fill in with building clouds and rain.

FAA guidance states that a thunderstorm should be circumnavigated by at least 20 NM on the upwind side, and if deviating to the downwind side you should add the speed of cell movement to that number.

If deviating isn’t possible due to an extensive system of hazardous weather, the only alternative is to divert to an alternate destination. Making the decision to deviate or divert should be accomplished well before it becomes absolutely necessary in order to maintain adequate safety margins.Using all available resources to develop a mental picture of the hazardous weather is the first step in this process. The next step is to use effective decision-making skills to choose the optimal course of action to eliminate or mitigate the threat.

Deciding on the optimal course of action involves exploring the available alternatives, and then choosing the alternative action that represents the most conservative outcome. Exploring these options takes time, which is a good reason to ensure that your mental picture of the weather ahead includes ranges that allow adequate time for decision-making, and then for taking the necessary actions to avoid weather threats.

KEY POINT: You need to have an adequate assessment of the weather threats at sufficient range to allow time for effective decision-making.

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