I've tried to find a similar problem on these message boards with no luck. 
I have a 99 Outback.  This only seems to happen after the car is warm, i.e. driven for 10-15 miles.  Everything seems fine while driving.  Then I stop at a stoplight or park in a parking lot and in about 30-45 seconds the engine temperature will go from normal (in the middle) to the top of the gauge.  If I start to drive it will go back down to the normal range.  I did find a fuse blown and replaced it (SECONDARY FAN, in Engine compartment).  It hasn't blown again, could've been blown when I bought it.  I've had it for 4 months now.   
  
Any ideas? 
  
Thanks, 
Brian