Clouds, fronts and convection — transcript

00:00:00.400 --> 00:00:05.598 Clouds, fronts and convection: reading the sky before you fly.

00:00:05.948 --> 00:00:10.306 Cloud forms when moist air rises and cools to its dew point.

00:00:10.306 --> 00:00:15.091 The water vapour condenses onto tiny particles, like dust or salt.

00:00:16.448 --> 00:00:22.756 Four things lift air: convection from a heated surface, terrain forcing it uphill,

00:00:22.756 --> 00:00:26.479 a front, and convergence, where airstreams meet.

00:00:27.448 --> 00:00:33.038 Cumulus is heaped: rising, unstable air. Stratus is layered: stable air,

00:00:33.038 --> 00:00:38.168 often with a low grey ceiling. Reports give cloud amount in oktas,

00:00:38.168 --> 00:00:39.700 eighths of the sky.

00:00:40.448 --> 00:00:46.704 Height gives the prefix. Cirro clouds are high and made of ice crystals.

00:00:46.704 --> 00:00:53.475 Alto clouds sit at middle level. Low cloud includes stratus and stratocumulus.

00:00:53.475 --> 00:00:55.103 Nimbus means rain.

00:00:55.453 --> 00:01:00.690 Some clouds grow tall: cumulus, towering cumulus, then cumulonimbus,

00:01:00.690 --> 00:01:04.410 the thunderstorm cloud. Treat it as a stop sign.

00:01:04.410 --> 00:01:07.522 The weather hazards video covers storms.

00:01:07.872 --> 00:01:12.606 Cumulus growing taller while you fly? The air is unstable.

00:01:12.606 --> 00:01:16.779 Expect turbulence underneath, and be ready to land.

00:01:17.129 --> 00:01:20.186 Quick check. Which part of a cloud's name means rain?

00:01:22.329 --> 00:01:24.132 Nimbo, or nimbus.

00:01:25.629 --> 00:01:30.164 An air mass has even temperature and humidity. Maritime air is moist,

00:01:30.164 --> 00:01:33.597 continental is dry. Tropical is warm, polar is cold.

00:01:35.129 --> 00:01:38.838 A front is where two air masses meet. At a cold front,

00:01:38.838 --> 00:01:42.681 cold air pushes under the warm air and lifts it sharply:

00:01:42.681 --> 00:01:47.198 a narrow band of heavy showers and gusts, sometimes thunderstorms.

00:01:48.629 --> 00:01:52.654 At a warm front, warm air slides gently up over the cold.

00:01:52.654 --> 00:01:57.720 Expect a wide area of layered cloud, steady rain and reduced visibility.

00:01:58.629 --> 00:02:03.296 Cold fronts regularly sweep across southern Australia in winter.

00:02:03.296 --> 00:02:08.321 One on today's forecast? Expect gusts and heavy showers as it passes.

00:02:08.671 --> 00:02:13.190 Dark surfaces, like bitumen and ploughed fields, heat fastest.

00:02:13.190 --> 00:02:17.709 Warm air rises from them in thermals, often topped by cumulus.

00:02:18.271 --> 00:02:24.815 In a thermal, the drone is pushed up. In the sinking air between thermals, it drops.

00:02:24.815 --> 00:02:27.048 Lighter drones feel it most.

00:02:27.671 --> 00:02:31.882 Thermals peak on hot, sunny afternoons. Early morning is smoother,

00:02:31.882 --> 00:02:34.019 and overcast skies suppress them.

00:02:35.171 --> 00:02:40.432 Recap. Rising air makes cloud. Heaped is unstable, layered is stable,

00:02:40.432 --> 00:02:46.519 nimbus means rain. Cold fronts are narrow and intense, warm fronts wide and wet.

00:02:46.519 --> 00:02:48.624 Cumulus marks the thermals.

00:02:48.974 --> 00:02:52.344 Final check. When is the air usually smoothest?

00:02:53.774 --> 00:02:55.942 Early morning, before the ground heats up.