Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2008/05/16 23:02:35 #Date/time of acquisition
WS=    6.59   #Wind speed (knots)
WD=   70.11   #Wind direction (degrees) (0-360)
T =    1.07   #Temperature (degrees celsius)
RH=   55.01   #Relative humidity
BP=  618.52   #Barometric pressure (millibars)