"W"-shaped erratically flying at low level is "unidentified" with anything prior seen in thousands of flight hours.

The Tempe Arizona sky was clear with many stars and planets visible and moon at 74% illumination.
Suddenly at very low level (just above tree tops) a flight was observed moving from southwest to northeast, proceeding in a "rounded" zig-zag pattern with quick turns and slight variations in altitude.
Initially it looked like a blurry/hazy white "W" and I wondered if it were an owl initially.  As it quickly came closer it clearly was not a flight of birds or bats not an identifiable bird; and the "W" resemblance was assured, moving with the "W" parallel to the ground and moving toward the two points at the bottom of the W.  No typical banking maneuvers were noticed, meaning the object did bank and/or pitch up, just not with the co-ordination nor symmetry associated with fixed-wing aircraft nor fowl.
As it neared, still flying erratically, the object looked a muted white even translucent.  The "W" was not with sharp lines/edges, rather more rounded and muted/hazy with visible striations fore to aft along its entirety every 5% or so.  The flying "W" appeared as one unit, no flapping, no noticeable moving parts, no exhaust or trail of any sort, no lights nor glowing and no noise.
The object proceeded to nearly overhead the open patio and as I stood up it quickly altered course and went over/behind a 30' tree (which provided perspective & parallax, so I report it at low level).
I walked over under the tree and observed the object completing a turn back toward the tree. As I walked toward it, it turned away and proceeded back on a zig-zagging northeasterly track.  Observer has seen some very large white owls in Arizona, and this was not that.  If it was organic, nothing distinguished it as such.  Observer had previously observed what were deemed "The Phoenix Lights" on more than one occasion, including during daylight hours.  This "W" is quite unlike those phenomena.  
Observer's background includes many thousand hours of commercial piloting experience.