Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/23 14:55:38 #Date/time of acquisition
WS=   15.04   #Wind speed (knots)
WD=   33.22   #Wind direction (degrees) (0-360)
T =    7.46   #Temperature (degrees celsius)
RH=    8.43   #Relative humidity
BP=  615.61   #Barometric pressure (millibars)