Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2008/11/20 15:22:57 #Date/time of acquisition
WS=    7.52   #Wind speed (knots)
WD=  203.38   #Wind direction (degrees) (0-360)
T =    0.95   #Temperature (degrees celsius)
RH=   79.42   #Relative humidity
BP=  613.80   #Barometric pressure (millibars)