The Avenue
Heavy Air Comment

updated 3/2015

copied from: http://scpa.info/bb/forum/viewtopic.php?f=1&t=3177#p9410
posted by sd » Sun Mar 22, 2015 10:43 pm

gracecab wrote:
hoping for the "it's too cross at Bates, so I'm going to see if the Avenue is picking up any of this lift" just wasn't happening

Tom Truax Reply

I wasn't focused on the weather today, but did look at Bates late in the afternoon. I think the reason it was cross at both Bates and the Avenue is because the air was "heavy".

There was actually a decent lapse rate early under a lowish inversion, and I heard reports of pilots popping up for a short period at Elings, but once the onshore flow became established it was too cool compared to the air above it.  When the air is heavy, or stable, it is steered by the topography contours.  It will blow parallel to the coast along the Rincon, but then turn to go up the rivers.  As noted during your tutorial, when the air is heavy it will still be soarable at the tip of the ridge (The Cross), but the ridge itself is acting like a guide vane and steering the air. Further up the guide vane toward the upper launch the air has been turned so it will be cross.

On days with heavy air it will often be more soarable with a better direction when the wind first pulls in.  This is true for Wilcox, Bates, Elings, and the Avenue.  Once the airflow has established it tends to cross up and follow the contours. Since it is heavy, it wants to go around obstacles rather than over them.