Wasm season | Radical changes to weather systems, airflow through airports, and hailstorms heading towards Saudi Arabia

Arab Weather - Sinan Khalaf - As October approaches, memories of the "Wasm" rains, known for their thunderous nature, begin to emerge, reflecting on the soil, which quickly becomes covered with plants, announcing the end of the summer and drought months.

When does the tagging start?

This year's "rainy season" begins on October 16th and continues until December 6th, lasting 52 days. It is named thus because it brings greenery and vegetation to the land. If rain continues during this period, it is followed by a special spring and the appearance of truffles.

Tag entry signs

There are several clear signs of the onset of Wasm, including: Migratory birds begin crossing the skies of the Arabian Peninsula, Sidr honey is harvested, clouds move from west to east in response to the western jet stream, and the weather moderates significantly at night due to the apparent southward movement of the sun. There are also moderate dust waves resulting from upper depressions descending towards the region.

The start of the season and the decline of the seasonal depression:

With the onset of the Wasm season, the seasonal depression begins to recede and retreat, gradually being replaced by the Arabian high pressure system, which is largely responsible for pushing humid air masses from the Arabian Sea towards the Kingdom. This coincides with the presence of the Red Sea low pressure system to the east, which leads to a gradual and continuous drop in temperatures and a break in the intensity of the hot weather.

The tag and the beginning of the Red Sea low activity:

Al-Wasm is considered the beginning of the actual activity of the Red Sea depression, as it begins to deepen to affect the Levant and the northwestern parts of the Kingdom. The Red Sea depression also creates atmospheric instability, as it pulls the wet masses rushing from the Arabian Sea and pushes them towards the Kingdom, where they interact with the low-pressure systems coming from the north and the Levant region, generating a state of atmospheric instability that leads to the formation of thunderclouds and rainfall.

The impact of Mediterranean depressions:

The increasing activity of the European high pressure system is pushing cold air masses towards the eastern Mediterranean basin, responsible for the formation of extratropical depressions or Mediterranean depressions. The Red Sea low pressure system interacts with the cold Mediterranean depressions, which contribute to the development of unstable conditions and rainfall, which may be thundery and heavy.

The direct impact of the Siberian high on the region at the end of the season:

At the end of the Wasam period, the Siberian high begins to directly affect the Kingdom, causing a significant drop in temperatures, which calls for wearing winter clothing. Temperatures drop, especially at night.

From the memories of the tag

Strong floods occur frequently during the Wasm period, the most recent of which occurred in November 2013 in the capital, Riyadh, as well as in large areas of the Kingdom, when torrents formed and heavy rain continued to fall across large parts of the country. The largest floods in the Kingdom also occurred in November 2008, when heavy rain continued to fall for several days. The strength of the Wasm has been repeated in many years, most notably 2012, 2004, and 1997. The Wasm period can also be weak, as happened in the Wasm of 2010.