Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/22 15:28:47 #Date/time of acquisition
WS=    3.53   #Wind speed (knots)
WD=   38.37   #Wind direction (degrees) (0-360)
T =    3.55   #Temperature (degrees celsius)
RH=   15.70   #Relative humidity
BP=  615.17   #Barometric pressure (millibars)