The first route we'll look at is Calcutta to Singapore — Page 439, Lesson 409

I want to walk you through a new chapter — Chapter 23, Route Climatology. This is where we take all the meteorology we've studied and apply it to real, specific flight routes around the world. The first route we'll look at is Calcutta to Singapore. Let's start with the geographical considerations. This route sits between latitudes 23° North and 01° North. That's a significant span — from roughly the Tropic of Cancer down almost to the equator. The flight path overflies the eastern Bay of Bengal, and it runs just off the west coast of Bangladesh, Burma, Thailand, and West Malaysia. So you're flying over water for a good stretch, with land to your east. Now, the terrain features that matter here: to the north of low-lying Bangladesh lie the Himalayas. That's a massive mountain barrier that will influence weather patterns. Down the length of West Malaysia runs the Cameron Highlands — that's a mountain spine that runs north-south along the peninsula. And to the southwest, the island of Sumatra also has a mountain backbone. So you've got high terrain on both sides of the route in the southern portion. For winter, which is January in this part of the world, we have Figure 23.1 — that's "Weather and Winds in January" . This figure shows the surface pressure patterns, wind directions, and cloud conditions you'd expect along this route during the winter monsoon. The key point is that the winter monsoon brings northeasterly winds down from the Asian continent, and that interacts with the geography I just described — the Himalayas, the Bay of Bengal, and the mountain ranges of Malaysia and Sumatra — to produce the specific weather you'd encounter on this sector. That's the foundation for this route. We'll go into the details of what those winds and clouds look like as we move through the chapter.