4/7/97 Israel chase by David Shohami

From davidsh@mail.geocities.com Thu May  8 12:53 CDT 1997
From: David Shohami 
Subject: Re: Chase Report from Israel


Here's my latest chase, which occured at 4/7/97, mainly in Jerusalem, Israel:

        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.

        During the night, the winds shifted from NE to S. The trough was
becoming active. Instead of bringing hot dry winds from the eastern deserts
of Syria and Jordan, the winds now brought great humidity from the Red Sea
in southern Israel. As I woke up that morning, there was not a cloud in the
sky, but I felt the strong humid southerly winds. My chase destination for
that day was Jerusalem, because I knew that when the hot humid winds reach
the Jerusalem mountains, they will cool considerably and some convection has
to happen.

        In about 9:30, a few cumulus clouds appeared. The temperatues were
rising, and already reached 22 degrees Celsius (72F). The cumulus weren't
showing great convection, though. I went to southern Jerusalem to get a
better view, and I noticed a short line of altocumulus, with towers shooting
up and down. The time was 13:15. I watched the line, which quickly developed
a very dark, flat updraft base. The temperatues were now 28C (83F), which is
very warm for this time of year in Jerusalem. Soon, one tower developed an
anvil, and an alto-cumulonimbus cloud developed. It did produce some severe
winds and hail, for a short time, but unfortunately it died, as the rain
entered the updraft area.

        Disappointed, I turned back to the cumulus - and fianlly they were
towering. I chased one tower, which was to the SW of Jerusalem, and then I
saw another towering cumulus farther S. It looked hard, but I couldn't see
the updraft base. I decided to leave it and stick with the one I was
chasing, which was now to my W. If only I knew how wrong I was...

        The towering cumulus I was chasing developed nicely, and at 16:45
the first rumble of thunder was heard, as a large anvil extended above me.
The dark updraft base was completely rain-free. I drove to a high point
where I could see better, and then I suddenly saw the tower from earlier,
which was still to my S. It developed to a beautiful severe supercell, which
was moving very slowly NE. I thought about chasing it, but it was too far
away. I decided to turn to the other cell, and hope it will develop. I
wasn't too disappointed, because I had a great view of the supercell, and
took some excellent photos. The cell I was chasing also started to look
promising. There was no rain at all, and there were lots of CGs. A small,
rotating wall cloud appeared, but soon dissipated. A nice mammatus cloud was
also visible. I chased the cell for almost 2 hours, and still it wasn't
raining, and lightning was more frequent. The wall cloud appeared and
disappeared again. Then, at around 18:40, heavy marble size hale began
falling, and within minutes covered the ground. The cell collapsed, and a
mixture of heavy rain and hail began to fall. Half an hour later the cell
became very weak, and I turned back home. It was 19:15, and I didn't think
it could develop again.

        All in all, not a bad chase. I got beautiful photos of the supercell
I missed, the alto-cumulonimbus cloud, and the wall cloud. The days that
followed produced many severe cells in Jerusalem.

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