"Backward" winds around Seattle make for "backwards" Convergence Zone
SEATTLE -- It's not often we can pull off a convergence zone on a sunny day, but Tuesday was a special case -- in fact, it was a "backwards" convergence zone (or "reverse" zone).
Typically our pesky convergence zones are caused by west/northwest winds coming off the Pacific Ocean, getting split around the Olympic Mountains, and colliding over the Seattle-Everett corridor. The colliding winds cause updrafts, which in turn create condensation, clouds, and sometimes really crazy precipitation.
But on Tuesday, the winds were backwards. We had a strong easterly wind developing as cold, dense air in Eastern Washington created higher pressure there. The east winds were once again splitting around the Olympic Mountains, only this time colliding on the western side, out over the Pacific Ocean.
The process isn't as dramatic -- it's just causing a line of low clouds, but at least it marks its presence: