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Interesting Last Day of Camp, 2015

posted Mar 5, 2015, 10:43 AM by Jason Arnold   [ updated Mar 5, 2015, 11:15 AM ]


"Yesterday (3/4/15), I was very sceptical about the forecast weather for Wednesday. I said that it is better to go the airport and see the rain falling than to stay at home and watch the nice soaring weather through the window. The reason I did not believe the forecast was based on what is called the fœhn effect. The wind was forecast to be 240 degrees. I made the sarcastic comment that it was 240 degrees ± 20 degrees. It is what happened. Moreover, since we are at the foot of the mountains, the air becomes drier and heats along the dry adiabatic rate (g/Cp=9.75 K/km). As a consequence, we got a temperature of 24 C (75 F) and thus, it was unthinkable to get low stratus clouds on the lee side of the mountains. However, I did see the stratus layer at the South east of Marion at about 20 miles. The supposedly overcast weather turned into a nice weather (yet a little bit turbulent) and I encountered pretty violent rotors where I was going for + 10

knots to -10 knots in a few seconds flying at 43 knots. The dew point was 58 F and thus the "official cloud base" was supposed to be at 1100 m (3600 feet). I climbed at 6000 feet MSL (4800 feet AGL) and I was clearly below the cloud layer that I estimated to be at 6500 feet AGL. Thus these clouds were not cumulus generated by convection, but altocumulus generated by the wave/rotor system. Some clouds were curling and were obviously marking rotors. Marion has what is called a mesoclimate and it is why it is important to read forecaster discussion to get an educated opinion and adjust the forecast in consequence". - S4 (Submitted by: JJ)




Photo of actual Horseshoe vortex cloud above Shiflet Wednesday 
"The rarest and most fleeting of all the recognized cloud forms. The distinctive shaped loop with tails forms in a rolling vortex that was initially horizontal but becomes distorted upwards by convection"- Description of HVC by Ian Jacobs




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