Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2008/10/06 23:07:17 #Date/time of acquisition
WS=    0.02   #Wind speed (knots)
WD=  233.69   #Wind direction (degrees) (0-360)
T =    4.90   #Temperature (degrees celsius)
RH=   12.96   #Relative humidity
BP=  617.27   #Barometric pressure (millibars)