Raging wildfires have swept across central and southern Chile, claiming at least 11 lives and destroying more than 400,000 acres of forest over the past week. Reported as the worst disaster in Chilean history, the fires were aggravated by a combination of strong winds, historically high temperatures and almost a decade of drought.
In the presently arid and water-scarce environment of Chile, the relative humidity of the atmosphere (the ratio of the amount of moisture present in the air to the amount needed for saturation at the same temperature) is extremely low. This, together with extreme summer temperatures and gusty winds, ignites the flames, and drives the rapid, widespread burning.
In Australia, parts of New South Wales and Victoria have been placed on a total fire ban as winds gust over 40mph and daytime temperatures exceed 40C. Sydney has had nine days hotter than 35C, with night-time temperatures not budging below a relentless 30C.
Meanwhile, the Midwest of the US has been engulfed in a blanket of cloud, from sunrise to sunset, for more than a week. Many places have had average cloud cover of 100%, or eight oktas, for eight days straight.
This is because of the jet stream plunging southward, allowing warmer, moist air from the southern states to glide over the colder, snow-covered Midwest, creating a temperature inversion within the atmosphere. Thus, air becomes saturated, and condenses to form banks of thick, low-lying cloud and advection fog, which is not likely to disperse until the wind direction changes.
