Important information: The difference between a low-pressure system and a state of instability

Arab Weather - In this article, we offer a simplified scientific explanation of the weather systems that affect Jordan, as a lack of familiarity with meteorological terminology can cause some confusion. This report will cover both low-pressure systems and periods of atmospheric instability, clarifying their characteristics, formation mechanisms, and how these phenomena directly impact the weather in the Kingdom.

What is a low-pressure system?

A low-pressure system is formed as a result of low atmospheric pressure in a particular area, creating a broad and organized weather system that moves along a specific path from one area to another, carrying with it a range of weather phenomena such as rain, low temperatures, and wind activity.

For example, when a low-pressure system begins to affect Jordan, it usually forms over other regions, such as the central Mediterranean, and then gradually moves eastward to reach the Levant coast. It can be clearly observed through satellite imagery and remote sensing systems, allowing its movement and center to be tracked. As it moves in an organized manner, the accompanying weather activity gradually spreads, with rain falling first in the north of the Kingdom, then extending to the central regions, before reaching the south and east of the country.

The low-pressure system is characterized by its wide and regular effects. The clouds that accompany low-pressure systems are known as stratocumulus clouds, which cover a wide area and produce winter rainfall that may last for several hours, often with regular intensity, and foggy conditions due to the low base of these clouds.

What is a state of atmospheric instability?

Atmospheric instability forms through a mechanism entirely different from that of low-pressure systems. It arises when warm air rising from the lower atmosphere (closer to the Earth's surface) meets cold air descending from the upper atmosphere over a limited geographical area, coinciding with the presence of atmospheric moisture. This convergence creates an unstable environment that promotes the formation of cumulonimbus clouds.

Atmospheric instability is accompanied by the formation of cumulonimbus clouds. These clouds develop vertically to high/total heights in the atmosphere, and their thickness increases significantly, leading to a range of strong and varied weather phenomena depending on the strength of the situation.

Weather phenomena associated with periods of atmospheric instability:

Thunderstorms.

Heavy rainfall showers over a short period of time and in limited areas.

Downdrafts and strong winds.

Sandstorms or dust storms, especially in the desert.

Hail showers fell, sometimes quite large.

The unstable weather conditions are characterized by the fact that their impact does not include all regions of the Kingdom as happens with low-pressure systems, especially those of advanced degrees, but rather they are confined to narrow geographical areas. A region may witness a strong thunderstorm while a region close to it remains without rainfall or witnesses less intense rainfall.

During periods of atmospheric instability, the risks of flash floods and torrents increase. What do we mean by flash floods and torrents?

Flash floods:

These are flash floods that form very quickly after heavy rainfall in a limited area and within a short period of time. They are considered one of the most dangerous types of flash floods because they occur suddenly, and often sweep away everything in their path, including vehicles, people, and property. These flash floods usually occur in mountainous areas, slopes, or cities with weak drainage infrastructure, and the rain is the direct cause of them.

Runoff Floods:

These are the floods that reach an area that has not witnessed rainfall. These floods come from distant areas, meaning that their source is usually from the high mountains towards the valleys and low areas. This water moves through the valleys and channels that it has previously dug to reach low areas, and it may surprise the residents there even though the weather there may be stable.

And God knows best.