A Wind Called Joran

“At times Joran south of Jura Mountains”, do you know what this means? I did not and that’s why I made a note on my weather briefing to find out after the flight. On descent into the aerodrome of Neuchâtel nature answered my question – by simply turning my stomach upside down.

Joran-Fallwind

Flight Planning

For my first solo cross-country I chose a very easy route. Grenchen to Neuchâtel is a flight of just 20 minutes. When I checked the weather early in the morning it seemed good but windy and it was forecast to detoriate during the afternoon. The wind data ranged from 3 knots steady  to 15 knots with gusts up to 22 knots. Sadly uncontrolled airports in Switzerland have no automatic weather observation. Only one station reported gusts and I had plenty of fuel to turn around and fly home again. The TAFof Grenchen predicted 240° at 10 knots wich would be nicely on the nose.

The Flight

I switched to the tower frequency as number two for departure. Many students were in the air and I could imagine how this poor guy felt when tower told him to “keep up your speed, keep it rolling, keep it rolling”. Another one was on short final rolling between a bank of 30° left and right. It looked scary. The Cessna in front of me was probably working on page number 15 of its checklist. Tower finally asked him if he was ready in two minutes. He responded that he was ready and needed a backtrack. On his way back the tower asked me if I was ready for an immediate departure. The airplane was light, only I was onboard and the stiff headwind would take me aloft even earlier. I took off and climbed to 4500 feet. I was flying below a cloud that formed south of Jura and I noticed that the airplane suddenly flew at a nose high attitude. My speed was 20kts lower than normal. I was puzzled. After a few minutes I realized this was air flowing downwards and I was actually climbing against it. After a very short cruise and talking to Payerne tower I descended into the circuit of Neuchâtel. I could not see the windsock so I looked out for other clues. Clue no.1, I had a very large crab angle when I flew overhead. Clue no.2, on base I was low enough to see wind streaks. Wind streaks form at 8 knots or more and build parallel to the wind. Clue no.3, many waves had white caps. White caps begin to form at 12 knots and if there are many of them it would be around 15 knots. And additionally many gusts were visible appearing as dark shadows caused by patches of many little waves. Okay, I had more or less 15 knots almost direct from the right. On short final the windsock told me the same. The air was rather turbulent and I kept my speed 10mph faster than on a normal approach. I flew over the trees a bit high to avoid the gusts. I established crosswind corrections, kept the airplane aligned with the center line using rudder and correcting with bank for sideways drift. I ended up applying a lot of rudder. Even full rudder for a second or two. Then things seemed to calm down a little and I flared with the right wing low, waiting for the right moment to touchdown. I didn’t like it. I floated and floated. Before I reached the middle of the runway I decided to go around. Full power, attitude, speed, establish climb and flaps slowly up. Now while climbing the turbulence got worse. There was no way to give it another try. On my next call I transmitted that I was leaving the circuit and heading back to Grenchen. I was happy with my decision making. No need to try it again!

The flight back went by fast as I had a tailwind in excess of 30 knots. Back in the circuit I spotted the Piper Seneca that was parked in front of me in the hangar. On short final I was relieved to feel a steady wind. 280 degrees at 15 knots cleared to land runway 25 – this was the most beautiful part of this flight. My concentration was high after the rodeo ride in Neuchatel. I touched down on centerline, right wheel first and applied more and more aileron during rollout. All the way back to the hangar I used crosswind corrections and for the first time I felt that it really helped a lot to keep the wings and tail down.

Now I needed a coke. I always drink coke when I feel dizzy. 😉

The Seneca pilot returned as well and while I was cleaning the windshield we had a little hangar talk. I told him where I went and that I did not land there because it was too windy. He responded that he heard of incidents caused by the Joran and that he saw it the first time forecasted today in a synopsis. I told him that this was the only thing that I did not understand in todays weather briefing. He explained that it was a fall wind that flows down on the south side of Jura. I learned a big lesson: Never ever ignore something unknown in the weather forecast if it happens in the area you intend to fly.

Nonetheless, I am very happy with this experience today. The flight was safe at all times although it told me to be cautious on every flight – which is not a bad thing at all.

The Joran

Local winds are often named. You probably know the Chinook, the Bise or the Mistral in France. Joran is pronounced the french way and here is, what it is:

Der Joran – Ein Fallwind am Jurasüdfuss

Diploma Thesis by Ferenc Baki

The Joran is a katabatic wind which arises along the southern slope of the Jura mountains.
Especially the surfers and sailors on the lakes of Biel and Neuchâtel in Switzerland are afraid
of the gusts of this wind. There exist two dierent types of Joran: Joran dynamique and Joran
statique.

The investigations showed, that the Joran statique appears on fair weather days in summer,
when the pressure North of the Jura mountains in the evening hours is lower than the pressure
South of the mountains. The velocity of the gusts and the mean velocity of the wind in
the Joran phase is strongly dependend on the maximum temperature dierence between the
mountain station Chasseral and the station Neuchâtel. Between this temperature dierence
and the wind velocity in the Joran phase exists a strong correlation.

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