README file for CU/NOAA fog product
Contact: Matthew Shupe. Matthew.shupe@noaa.gov, 303-497-6471
Methods:
The methods used to identify fog and precipitation are given here. They are entirely subjective and
qualitative in nature.
Fog: Possible categories are No Data, No Fog, and three fog classes ranging in likelyhood that fog is
actually present (arbitrarily defined).
1) Fog = -1 (“No Data”): There is insufficient data to make a determination.
2) Fog = 0 (“No Fog”): No conditions outlined below are met
3) Fog = 0.5 (“Possible”): ODEN visibility measurement is less than 5 km
4) Fog = 0.8 (more than possible): ODEN visibility measurement is less than 5 km and the
ceilometer cloud base (either NOAA or ODEN ceilometers) is less than 100 m AGL.
5) Fog =1.0 (“Likely”): ODEN visibility is less than 1 km OR visibility is less than 2 km and the
ceilometers cloud base is less than 80 m AGL.
Precipitation: Possible categories are No Data, No Precip, or Precip.
1) Precip = -1 (“No Data”): There is insufficient data to make a determination.
2) Precip = 0 (“No Precip”): Measurements do not meet any of the precipitation requirements
given below.
3) Precip = 0.5 (“Possible”): Cloud radar sees at least 0.3 km of total cloud thickness and the
lowest level reflectivity is greater than -15 dBZ and/or the lowest level radar mean Doppler velocity is
greater than 1 m/s.
4) Precip = 0.8 (more than possible): Lowest radar return is below the ceilometers cloud base,
total depth of radar returns is greater than 0.3 km, lowest level radar reflectivity is greater than -15 dBZ
and the lowest level radar mean Doppler velocity is greater than 1 m/s
5) Precip = 1 (“Likely”): Radar reflectivity in either of the lowest two range gates is higher than 0
dBZ or the lowest level mean Doppler velocity is greater than 1.5 m/s.
Fog Images:
Each daily image has 6 panels of information. 1) The ODEN’s visibility measurement in km; 2) Cloud
information from the ODEN’s ceilometer - when a cloud base was reported it is given as red dots and
when the visibility mode was reported it is given as blue dots, in km AGL; 3) Cloud information from
NOAA’s ceilometer - when a cloud base was reported it is given as red dots and when the visibility mode
was reported it is given as blue dots, in km AGL; 4) Cloud information from NOAA’s radar – the lowest
hydrometeor base is in red and the total cloud thickness is in blue (values greater than 1 km appear as 1
km), in km AGL and km, respectively; 5) Number concentration from the FSSP mounted on the ODEN –
total concentration is in red while the total concentration minus the first bin is in blue; 6) Identification
of fog and precipitation. For precipitation (red) the possible options are NoData, No Precip, or three
different levels of Precip corresponding to different likelihood. For fog (blue) the possible options are
NoData, No Fog, and three different characterizations ranging from Possible to Likely Fog.
Fog Data Files:
These are daily files that contain three columns. 1) Time in decimal hours [UTC]; 2) The fog
classification; 3) The precipitation classification.