Stealth Object Creeping Over Phoenix

I was standing on my back patio looking due east into a partly cloudy sky when a dome shaped object that looked EXACTLY like a very small piece of cloud went flying by at a speed of about 300 knots.  Its trajectory was north to south at an altitude of about 1000 feet AGL.  The object was flying level straight in open sky and was approaching a cloudbank.  Just before it reached the clouds it morphed instantly from a 'dome' shape into a 'diamond wedge' and seem to become more transparent, disappearing into the clouds all together.  This was no rogue cloud caught in a fluke wind stream; it flew with a purpose and sense of stealth.  Its flight path was directly under Sky Harbor's approach route and a commercial airliner flew over a few minutes later.  I estimated the size of the object to be that of 2- 3 jumbo jets in length and height.  My girlfriend also witnessed the object and was as stunned as I.
((ADDENDUM FROM WITNESS--MAY 03, 2010.))
Dear Mr. Davenport,
Almost 5 years ago I filed a report with NUFORC concerning a cloud shaped/textured object over Phoenix.  Tonight I had some free time and thought I would (after all these years) go back and visit my report.  I was shocked to see that it had been labeled a 'HOAX.'  I can't tell you what I saw that night, but myself and my wife DID see something very strange as described in the report.   In the spirit of truth and disclosure I would please ask you remove the 'HOAX' tag, as this was an honest and accurate report.
Sincerely,
((name deleted))
Boise, ID
http://www.nuforc.org/webreports/038/S38625.html
((END ADDENDUM))