Final stage check and extreme weather

8/18/2012

I did my final stage check for my Instrument Rating with Adam Moore to make sure I felt ready.  We departed VUO on an IFR flight plan and flew direct BTG.  I climbed up to 4000' and went into the published hold climbing to 5600' for the procedure turn for the VOR approach to SPB.  All was going well.  The approach to SPB went well and then I executed a missed approach.  I contacted the tower and let them know that I was on the missed and they assigned me 3000'.  Upon reaching that altitude, I was then assigned 4000'.  I went to full power and pitched up and had a 700' per minute climb.

About 4 miles from BTG the VSI dropped to -500 ft per minute.  I checked my pitch and I was still up 7 degrees, Power was still full at 2700 RPM, and my airspeed was 90kts.  This configuration should give a nice steady climb.  Were my altimeter and VSI failing?  I pulled the alternate static source and noted a very slight change then back to the indications I had before.  No carburetor ice as I was still making full power.  While I was checking and double checking everything, I recieved a radio call from ATC.  "Confirm you are climbing to 4000'?"  I responded that I was unable to comply and that I needed an immediate diversion to VUO.  ATC cleared the airspace for me and I returned to Pearson Field (VUO) for landing.  a few miles away from BTG I noticed that I could climb easily.  What ever was going on was very localized.  Upon landing, I called ATC on the radio and told them I was safely on the ground and thanked them for their help.  They then asked for a description of what happened.  I explained it to them and they thanked me for the information.  Less than a minute later I hear a 737 radio the tower that they are in the vicinity of BTG and are experiencing a 2000' per minute down draft.

I can now say I have experienced a micro burst.  A rare weather phenomenon associated with thunderstorms.