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    A trough of low pressure from tropical Africa extended all the way to Israel, through the Red Sea. This happens every year during autumn and spring, and it usually just produce a rise in temperatures and dry weather, with hot, dry easterly winds. But, on average, about 3-5 days a year, this trough becomes very active, and brings destructive weather. This year, the trough was active for over two weeks.

    In May 9 I noticed for the first time that the Red Sea Trough was starting to build itself in the region. The days were hot, like most May days in Israel, and temperatures reached the high 20s or even 30 degrees Celsius. But on that day huge cumulus towers appeared out of nowhere in the afternoon. Although they haven't developed to any storm, this was not like every May day. The weather maps started to show a trough from Ethiopia extending to southwestern Saudi Arabia and Yemen, and large blobs of cloud, probably Cb, were showing in those regions almost every afternoon in the visible satellite pictures. I knew that the Red Sea Trough has arrived, and the spring chasing season has started. But, usually it takes the trough a few weeks to reach Israel, so I just waited for it.

    May 13 was the Israeli Independence Day. I never thought it would turn out to be a nice chase day. I went to a friend's house at around 11:00 and we climbed to his roof to watch the air show that would soon begin. There was a great view of eastern and southern Jerusalem from his roof. It was very hot, already 28 degrees, and also very dry. But what I didn't know was that during the night the Red Sea Trough was growing, and it's center had reached the border between Jordan and Saudi Arabia. That meant winds from the SE instead of the normal easterly winds, and more humidity in mid-levels.

I had a hard time concentrating on the air show, because Alto type clouds filled the sky. Beautiful virga was falling from them, sometimes even light rain reached the ground. I knew this had something to do with the trough, because Alto clouds are the striking feature of the trough, as the humidity is very high in the mid-levels, and the air near the ground is very dry. Most storms associated with this trough are from Alto-Cb clouds.

    After the air show I had to go back home, but I didn't stay there for long. I drove after these Altocumulus clouds, but no storm developed that day. The core of the trough had not yet reached Israel. But the next three days did produce severe storms in Israel, and that's in the next chase report.