Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/23 10:07:17 #Date/time of acquisition
WS=    8.21   #Wind speed (knots)
WD=   44.19   #Wind direction (degrees) (0-360)
T =    7.52   #Temperature (degrees celsius)
RH=    7.09   #Relative humidity
BP=  617.04   #Barometric pressure (millibars)