Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/24 00:04:16 #Date/time of acquisition
WS=   16.01   #Wind speed (knots)
WD=   63.79   #Wind direction (degrees) (0-360)
T =    1.54   #Temperature (degrees celsius)
RH=    8.13   #Relative humidity
BP=  616.67   #Barometric pressure (millibars)