Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/07 04:44:40 #Date/time of acquisition
WS=    8.10   #Wind speed (knots)
WD=   17.78   #Wind direction (degrees) (0-360)
T =    2.42   #Temperature (degrees celsius)
RH=   30.25   #Relative humidity
BP=  617.26   #Barometric pressure (millibars)