A Meteorology Puzzler

David Schwartz of Albuquerque, New Mexico, writes:

Marilyn: A very strict boss of a Buffalo, New York, television station fires the meteorologist for saying that the low of the night would be -20 degrees because he didn't say Fahrenheit. The next day, his replacement predicts that the low would be -30 degrees, and she gets fired for the same reason.

On the following day, the new meteorologist states that the low of the night would be -40 degrees. He does not get fired. Why?

Marilyn responds:

Any ideas, visitors? The answer will appear tomorrow.