Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/21 10:38:26 #Date/time of acquisition
WS=    0.03   #Wind speed (knots)
WD=  300.66   #Wind direction (degrees) (0-360)
T =    1.17   #Temperature (degrees celsius)
RH=   30.13   #Relative humidity
BP=  617.18   #Barometric pressure (millibars)