Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/07 09:06:27 #Date/time of acquisition
WS=    6.64   #Wind speed (knots)
WD=   40.58   #Wind direction (degrees) (0-360)
T =    5.99   #Temperature (degrees celsius)
RH=   18.41   #Relative humidity
BP=  618.64   #Barometric pressure (millibars)