There is an intimate relationship between the movements of the masses of air in the atmosphere and the presence, or not, of rainfall. In the irrigation fields of the Royal Irrigation Canal of Montcada, the arrival of masses of air from the Southwest and South is the cause, throughout all seasons of the year in most of the situations, and appear associated with rain storms of autumn.

The arrival of masses of air from the west, the Western winds, after the first pass over the hot plateaus, acquires, in the garden, a scorching character, with very high temperatures exceeding 40° C, and with a very low relative humidity, which can together sometimes have very harmful effects on crops.
On the other hand, the movement of air masses from the North-East is associated with cold, polar or Arctic mainland air waves, causing frost.
In autumn, the combination that occurs on the west shore of the Mediterranean, warm and moist air coming from the sea that is forced to rise sharply over the mountains of the interior, with another cold air mass in the upper layers of the atmosphere, results in a sudden, catastrophic process and sometimes in very heavy rain. So, in the agricultural garden, the probability that rainfall starts within a period of five days, increases notably from 50-70% at the beginning of the month of October, and up to 90% by the end of November. The causes of this phenomenon must be looked for in the relatively high sea surface temperatures, around 20° C, higher than the air averages, when they come together with an injection of cooler air, in general maritime polar air. Under these circumstances, along the cold front originates the production of a strong convective instability, and the result is the development of an orographic rain front of cumulus clouds with heights of over 6000 m.

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