Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2008/12/02 21:43:32 #Date/time of acquisition
WS=   13.03   #Wind speed (knots)
WD=   76.08   #Wind direction (degrees) (0-360)
T =    2.24   #Temperature (degrees celsius)
RH=   43.41   #Relative humidity
BP=  618.79   #Barometric pressure (millibars)