Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2010/02/09 16:41:12 #Date/time of acquisition
WS=   19.12   #Wind speed (knots)
WD=   49.70   #Wind direction (degrees) (0-360)
T =    7.24   #Temperature (degrees celsius)
RH=   13.44   #Relative humidity
BP=  618.76   #Barometric pressure (millibars)