Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/21 09:03:59 #Date/time of acquisition
WS=    1.03   #Wind speed (knots)
WD=   45.48   #Wind direction (degrees) (0-360)
T =    0.10   #Temperature (degrees celsius)
RH=   19.82   #Relative humidity
BP=  617.33   #Barometric pressure (millibars)