Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2010/02/09 16:48:43 #Date/time of acquisition
WS=   17.70   #Wind speed (knots)
WD=   58.87   #Wind direction (degrees) (0-360)
T =    7.03   #Temperature (degrees celsius)
RH=   13.26   #Relative humidity
BP=  618.72   #Barometric pressure (millibars)