Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2010/02/09 16:48:13 #Date/time of acquisition
WS=   16.83   #Wind speed (knots)
WD=   63.02   #Wind direction (degrees) (0-360)
T =    7.06   #Temperature (degrees celsius)
RH=   13.23   #Relative humidity
BP=  618.68   #Barometric pressure (millibars)