Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/07/03 21:49:52 #Date/time of acquisition
WS=   10.57   #Wind speed (knots)
WD=  292.42   #Wind direction (degrees) (0-360)
T =    2.42   #Temperature (degrees celsius)
RH=   21.80   #Relative humidity
BP=  618.61   #Barometric pressure (millibars)