It is possible! Negative temperatures are perfectly well-defined (see http://en.wikipedia.org/wiki/Negative_temperature). In fact, they are higher than positive temperatures. There is a discontinuity in the traditional temperature system at 0, and the highest possible temperature is 0-, i.e., zero approached from the left. The lowest temperature (the traditional "absolute zero") is 0+.

Perhaps a more sensible system is one that uses \beta = -1/kT to measure temperature, where k is Boltzmann's constant. This temperature scale runs from -infinity to +infinity, with no discontinuities.

-2147483648 is still probably a bug, though. :-)

Weird. It comes straight from the National Weather Service, so it must be something strange with their data. Some sanity checking would be advisable, though.