Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2008/05/17 03:14:00 #Date/time of acquisition
WS=    5.30   #Wind speed (knots)
WD=  121.42   #Wind direction (degrees) (0-360)
T =    4.32   #Temperature (degrees celsius)
RH=    5.39   #Relative humidity
BP=  616.99   #Barometric pressure (millibars)