Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2008/09/07 01:30:58 #Date/time of acquisition
WS=   14.58   #Wind speed (knots)
WD=   71.69   #Wind direction (degrees) (0-360)
T =    2.04   #Temperature (degrees celsius)
RH=    5.66   #Relative humidity
BP=  614.73   #Barometric pressure (millibars)