Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/23 14:33:04 #Date/time of acquisition
WS=   14.03   #Wind speed (knots)
WD=   45.64   #Wind direction (degrees) (0-360)
T =    8.28   #Temperature (degrees celsius)
RH=    9.35   #Relative humidity
BP=  615.54   #Barometric pressure (millibars)