Hal,
The thermometer is a scalar front panel object, and you are trying to wire a 1D array of data to it...that's why you are getting the broken wire. I recommend you either index out an individual element from the array by wiring both the Row and Column values of the Index Array function, or take an average of the points in the array and wire that average to your thermometer.
You can read the on-line help in LabVIEW to learn more about manipulating arrays. Good luck.
Darren