In one of our latest posts, we introduced you to our new ‘Weather Feature’, which lets you choose the weather on your route, or more precisely, you can choose what weather you want to avoid/prefer. For example, you can choose to prefer sunny areas and avoid rainy areas and our app gives you the perfect route for your needs.
Most of us, while driving our car, like to avoid navigating in rainy areas. There can be big differences in the driving experience when there is a heavy downpour or just a light drizzle.
Heavy rain can flood the street and send mud onto it, which can make your trip dangerous without the right vehicle and tires. Most weather-related crashes occur on wet pavement or during rainfall. The proportion of liability-relevant situations in traffic accidents on wet road surfaces is as high as 81 percent in the winter month.
Working on our ‘Weather Feature’ we thought a lot about rain and the different types it can have. There are 15 different types of rain, did you know that? We neither. There is so much to learn about precipitation. So, let’s give you a quick overview of the water from above.
But what is rain exactly?
First of all: Rain includes all forms in which water from the atmosphere meets the earth. Sounds simple enough. Rain is the result of water vapor condensing and precipitating, forming droplets that fall from clouds due to gravity. There is always water vapor in the air. Warm air has more water vapor than cold air, which is why it is often humid in the summer. The vapor becomes small water droplets and when enough of these droplets collect together, we see them as clouds. If the clouds are big enough and have enough water droplets, the droplets bang together and form even bigger drops. When the drops get heavy, they fall towards the earth because of gravity, and we get rain.
Did you know that it also rains on other planets? However, it looks a bit different. Head to Saturn to witness the rain of diamonds or to Venus to see the sulphuric acid rain. Have you heard of the beautiful, blue Exoplanet HD 189733b? No? The daytime temperature there exceeds 1000°C and it rains… glass! We prefer our good, old raindrops! Speaking of raindrops, did you know that those aren’t shaped like a teardrop at all? But we get ahead of ourselves, we come back to that topic later. So for now, back to earth.
The strength of rain can be divided into three categories.
- Light rain describes rainfall that falls at a rate of between a trace and 2.5 millimeters per hour.
- Moderate rain describes rainfall with a precipitation rate of between 2.6 mm and 7.6 mm per hour.
- Heavy rain describes rainfall with a precipitation rate above 7.6 mm per hour.
But we can differentiate between 15 types of rain, the following are the three main ones:
Relief rainfall (orographic rain)
Relief rain occurs when the wind lets humid air from the sea or flat land rise up the side of elevated land formations, such as large mountains. The lift of the air up the windward side of the mountain results in cooling, and ultimately condensation and precipitation. On the leeward side (downwind), there is often a rain shadow (a dry area) observed. Relief rainfall occurs in the tropics, subtropics, and temperate zones. It can last from hours to a few days, in rare cases several weeks.
The current record holder, for this type of rain, as recognized by the Guinness Book of World Records, is the cluster of hamlets known as Mawsynram in India. Moisture swept from the Bay of Bengal, condenses over this 1,491m plateau, in the Khasi Hills that overlook the plains of Bangladesh. The result is an astonishing average annual rainfall of 11,871 mm. Even the world’s biggest statue, Rio de Janeiro’s 30m tall Christ the Redeemer, would be up to his knees in that volume of water.
Convection rain is rain from clouds that form due to convection currents. Convection rain occurs primarily in the tropics and subtropics and temperate latitudes, including Germany, Austria and Switzerland during the warmer season. Depending on the geographical location, it can last between several minutes (cloudbursts) and several days (tropical rain).
In warm weather, large amounts of the water in the ground or on bodies of water evaporate. The resulting moist air masses close to the ground are transported upwards due to air currents (heat flows also caused by the heat on the ground). When they reach their saturation, clouds form. Under optimal conditions, very strong convection thunderstorms often form in just a few hours. These occur mainly in tropical, but also in many other areas of the world (especially during the warm season), often in the early to late afternoon.
Convectional rain mostly is the cause for this very nice smell you get, when raindrops fall on warm, dry earth – known as petrichor.
Frontal Rain (Cyclonic rain)
Frontal precipitation is the result of frontal systems surrounding extratropical cyclones or lows, which form when warm and tropical air meets cooler air. Frontal precipitation typically falls out of nimbostratus clouds, hanging low in the sky, while appearing dark and grey. This effect occurs in the subtropics and temperate zones.
When masses of air with different densities (moisture and temperature characteristics) meet, the less dense, warmer air overrides the more dense colder air. The warmer air is forced to rise and, if conditions are right, creates an effect of saturation, causing precipitation. Passing weather fronts often result in sudden changes in environmental temperature, and in turn the humidity and pressure in the air at ground level.
Warm fronts occur where warm air pushes out a previously extant cold air mass. The warm air overrides the cooler air and moves upward. Warm fronts are followed by extended periods of light rain and drizzle due to the fact that, after the warm air rises above the cooler air (which remains on the ground), it gradually cools due to the air’s expansion while being lifted, which forms clouds and leads to precipitation.
Cold fronts occur when a mass of cooler air dislodges a mass of warm air. This type of transition is sharper, since cold air is more dense than warm air. Precipitation duration is often shorter and generally more intense than that which occurs ahead of warm fronts.
- Avoid Precipitation
- Avoid Slippery Roads
- Avoid Storms
- Avoid Windy Areas
- Prefer Sunny Areas
Driving in the rain, just driving in the rain
If you do get caught in such a heavy downpour while driving, there are some things you might want to consider, to drive much more safer:
Use your headlights to be seen by other drivers and maintain a safe following distance, because braking distances are getting longer on wet streets. That’s why you also don’t want to speed, obviously.
If you begin to hydroplane, remain calm and do not make any sudden movements. Do not jerk your steering wheel, speed up hard, or slam on your brakes. Instead, let off the gas and steer the car straight or in the direction of the skid. Do this until you regain contact with the road.
Avoid flooded roads, if you don’t have the car to get through there safely. If you see a large puddle and are unsure of the depth of the water, don’t drive through it. You risk getting stuck or ruining your car.
And never drive through moving water. If water is crossing the road, turn around. It may not look like a strong current, but it could carry you off the road. Turn around, don’t drown.
If the rain comes down as hard as a wall, so you can’t see the road or the cars around you: pull over when it is safe to do so. Just wait it out. If you can’t see the road, put on your four-way flashers and find a safe place to pull off the road. Make sure you pull your car as far off the road as possible. Other cars may have trouble seeing the road too and might not see you.
Fun fact to pour over while waiting for the rain to stop: Raindrops are usually represented in the shape of a teardrop, but this is not true in reality. When raindrops first form high up in the atmosphere, they take on a spherical shape as the water molecules bind together held by surface tension. As they begin to fall their shape changes, while air resistance causes the bottom of the drop to flatten and curve resembling the shape of a jelly bean.