Never is. I use this link. It is usually a little higher at the SW, so at least you won't get your hopes up from a false high reading.
If anything, you might be happy it is more wind than reported on the below sensor.
Bayflite found this a couple years ago.
http://www.srh.noaa.gov/data/obhistory/KSPG.html

It spiked right at 8:30 or so.