Formally, a number of airline's ops manuals allow crews to disregard PROB30 forecasts for a fuel decision. For example PROB30 TEMPO 1217 +TSRA could theoretically be ignored in terms of taking extra holding fuel.
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In Private Flying terms, 1 time in 3 you'll find one of these looming over your turning point or destination.
No that's
not what it means. It means that there is a 1 in 3 chance that at
some time during the 5 hour period, there will be one of these looming over a particular place of your choosing. Since the duration of convective activity, particularly with a strong wind, is relatively short, the probability that it will be there when you want to be there is much smaller than 1 in 3.
so either don't fly or be prepared to vary your route or hold-off. ... Flexibility is the key to air power, someone once told me.....
I'd still agree with that 100%.