Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/23 21:10:25 #Date/time of acquisition
WS=   16.92   #Wind speed (knots)
WD=   51.59   #Wind direction (degrees) (0-360)
T =    2.60   #Temperature (degrees celsius)
RH=    7.34   #Relative humidity
BP=  617.33   #Barometric pressure (millibars)