Is the mild start to fall a sign of a strong rainy season?

Arab Weather - Autumn is one of the most important seasons of the year, as it marks the beginning of the transition from hot weather to more moderate weather in the Mediterranean and Middle East regions. Many questions are raised every year about the intensity of the rainy season and its connection to the moderation of autumn or the mild beginning of autumn. Is there a scientific link between the moderate beginning of autumn and the rate of rainfall during autumn and winter?

Is the mild start to fall a sign of a strong rainy season?

Arab Weather experts said that there is no scientific relationship between the moderate autumn or the mild start of autumn and the subsequent strong rainy season. To date, there are no climate studies or research that indicate the existence of this relationship, as the region was affected in some seasons by early rain and snowfall during the autumn, followed by dry winter months, and vice versa, as some rainy seasons began with a dry autumn, but the rainy season ended later with rainfall amounts higher than seasonal averages.

More precisely, the rainy season in the Mediterranean and the Middle East is linked to several factors and weather phenomena that affect it during the fall and winter, or the rainy season in general.

What weather phenomena affect the rainy season?

Arab Weather meteorologists said that several weather factors affect the region's climate during the fall and winter months, which we summarize as follows:

Arctic Oscillation (AO)

The Arctic Oscillation (AO) affects the region's weather, especially during winter. A positive AO results in cold air concentrating around the Arctic Circle, while a negative AO results in greater undulation of the polar jet stream and the spread of cold air further south, thus improving the chances of cold air and low-pressure systems reaching the region.

North Atlantic Oscillation (NAO)

The North Atlantic Oscillation reflects the atmospheric pressure in the North Atlantic, and this is also linked to the temperature of the water there. If the waters of the North Atlantic warm, this leads to a continued decrease in the atmospheric pressure there and the formation of what are known as Atlantic gyres (deep atmospheric depressions that form repeatedly and regularly) . This phase is considered the positive phase of the North Atlantic Oscillation, and it is usually not considered positive during the winter season in the eastern Mediterranean basin, as the formation of Atlantic gyres there leads to pulling cold air and preventing it from deepening into the region.

While the negative phase of the North Atlantic Oscillation is considered more favorable for the eastern Mediterranean basin, this means weaker Atlantic vortices and the formation of high atmospheric pressure in the central and North Atlantic, limiting the formation of deep depressions in that region.

Water temperature in the tropical Pacific Ocean (El Niño and La Niña)

El Niño and La Niña are considered among the most influential weather phenomena on the climate around the world due to their significant impact on the heat cycle, oceans, and atmosphere. The following is an explanation of these weather phenomena.

El Niño:

• It is a phenomenon that occurs when the temperatures of the tropical Pacific Ocean rise above their normal levels.
• This rise in sea surface temperature leads to changes in wind patterns and ocean currents, altering the distribution of rainfall and heat over large areas around the world.
• The result is drought in some areas and floods in others.
• Impact on the Eastern Mediterranean Statistics: Above-average temperatures in winter and above-average rainfall

La Niña:

• It is the opposite phenomenon, where the temperatures of the tropical Pacific Ocean are lower than normal.
• This low pressure increases easterly winds that push cold water toward the surface, affecting global weather patterns.
• The result is cooler, wetter weather in some areas and drier weather in others.
• In the eastern Mediterranean, this phenomenon is statistically associated with colder weather during the winter and rainfall that is below seasonal averages.

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One of the most important factors affecting the rainy season is the behavior of the atmosphere. Atmospheric behavior refers to the movement of the atmosphere and the undulation of the jet stream in some seasons. Some seasons are characterized by a smooth movement of the jet stream towards the south, which continues for most of the season and is the greatest influence on the condition of the rainy season, rainfall, and the formation of low-pressure systems in some areas. This is not to mention the significant influence of the weather phenomena mentioned above.

While the jet stream undulation is concentrated in some rainy seasons around the Arctic Circle and areas of western and northern Europe, which weakens the arrival of rain depressions towards the region.

How can we know the behavior of the rainy season before it happens?

Arab Weather experts said it's best to follow climate and statistical models to determine the shape of the rainy season. They also recommend following seasonal and monthly bulletins, which are updated periodically within the app, to stay informed of the latest developments. They are prepared by experts in this field.

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