Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/22 08:55:24 #Date/time of acquisition
WS=    5.82   #Wind speed (knots)
WD=   54.96   #Wind direction (degrees) (0-360)
T =    1.66   #Temperature (degrees celsius)
RH=   10.05   #Relative humidity
BP=  616.52   #Barometric pressure (millibars)