Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/23 21:14:46 #Date/time of acquisition
WS=   18.73   #Wind speed (knots)
WD=   48.36   #Wind direction (degrees) (0-360)
T =    2.66   #Temperature (degrees celsius)
RH=    7.46   #Relative humidity
BP=  617.33   #Barometric pressure (millibars)