Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/23 22:54:03 #Date/time of acquisition
WS=   15.01   #Wind speed (knots)
WD=   62.95   #Wind direction (degrees) (0-360)
T =    1.54   #Temperature (degrees celsius)
RH=    7.73   #Relative humidity
BP=  617.11   #Barometric pressure (millibars)