Part 107 exam practice question · Weather & METAR
TEMPO marks temporary fluctuations expected to last less than one hour at a time and, in aggregate, less than half of the period stated. Both halves of that definition matter. The one-hour-at-a-time limit distinguishes TEMPO from a lasting change, which would be written with FM or BECMG, and the less-than-half-the-period limit distinguishes it from conditions that dominate the window. So TEMPO 2324 2SM -RA BKN008 OVC015 forecasts that between 2300Z and 2400Z there will be spells of two statute miles visibility in light rain with a broken layer at 800 feet, none lasting a full hour and totalling under 30 minutes. For a remote pilot the planning consequence is specific: two statute miles is below the three-mile requirement and an 800-foot broken layer leaves only 300 feet of usable altitude, so during those spells the flight is not legal. Since the timing within the window is unpredictable, TEMPO conditions that breach a limit must be treated as possible at any moment in the period.
TEMPO describes temporary fluctuations lasting less than one hour at a time and totalling less than half the stated period, so the conditions occur intermittently within 2300Z to 2400Z rather than continuously.
In a TAF, TEMPO indicates temporary fluctuations expected to last less than one hour at a time and, in total, less than half the indicated period. Lasting changes use FM for rapid transitions and BECMG for gradual ones.
Under an Hour, Under Half. Each spell short, and all of them together still a minority of the window.
Distinguish TEMPO from BECMG and FM. Only TEMPO carries both the per-occurrence and the aggregate limitation.
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