The only exception to your theory is that San Antonio / Austin areas seems to get a good share of rain / humidity -- and I believe they are west of your imaginery line (if I calculated it correctly.
Cheers, Clutch.
“Another way of looking at your theory is examining forest lands in the US.”
Along with Hurricane tracks coming up through and originating in the GOM... and historical Tornado paths. Humidity indices are key. But it it somewhat of a SWAG.
I always thought the Cimarron Grasslands would be a nice place, if the water was good and plentiful.