1. Radiometrics Corporation 1 Fog Detection & Forecasting Using the the Radiometrics TV/WVP-3000 Temperature, Humidity & Cloud Liquid Profiling Radiometer April, 2003

2. Fog Forecast and Detection thru Radiometric Profiling Airports worldwide need a reliable operational system for fog forecasting Airports worldwide need a reliable operational system for fog forecasting Water vapor saturation near the surface is required for condensation of fog Water vapor saturation near the surface is required for condensation of fog Accurate fog forecast and detection is possible with radiometric profiling of relative humidity and cloud liquid Accurate fog forecast and detection is possible with radiometric profiling of relative humidity and cloud liquid

3. Feb ’01 Denver Case Study Flights were diverted from Denver International Airport for 18 hours during Feb 2001 because of fog event Flights were diverted from Denver International Airport for 18 hours during Feb 2001 because of fog event Traditional forecasts failed to predict fog Traditional forecasts failed to predict fog Radiometric retrievals of relative humidity increased to saturation during the 10 hours prior to onset of fog Radiometric retrievals of relative humidity increased to saturation during the 10 hours prior to onset of fog Accurate fog forecast and detection of onset was possible with radiometric RH and cloud liquid soundings Accurate fog forecast and detection of onset was possible with radiometric RH and cloud liquid soundings

4. Radiometric retrievals at Boulder showing arrival of cold upslope air below 500 m height and associated condensation of supercooled fog.

5. Radiometric RH retrievals (blue) increasing from 45% to saturation below 500 m height from 0000 to 1200 UTC on 16 Feb 01 at Boulder. The 0000 and 1200 UTC Denver radiosondes are shown for comparison (red).

6. Radiometric retrievals at Boulder (red) compared with radiosonde soundings at Denver (blue) during arrival of upslope and supercooled fog. [Start slide show to animate]

7. UCAR Assimilation Experiment Conventional MM5 forecast did not predict fog in Boulder or Denver on 16 Feb 2001 Conventional MM5 forecast did not predict fog in Boulder or Denver on 16 Feb 2001 Radiometric profiles at Boulder were assimilated into MM5 at UCAR, using variational analysis (4DVAR) Radiometric profiles at Boulder were assimilated into MM5 at UCAR, using variational analysis (4DVAR) Accurate fog forecasts were obtained for Boulder and Denver after assimilation of radiometric profiles* Accurate fog forecasts were obtained for Boulder and Denver after assimilation of radiometric profiles* *Vandenberghe and Ware, Proceedings International GPS Meteorology Workshop, Tsukuba, Japan, January 2003. *Vandenberghe and Ware, Proceedings International GPS Meteorology Workshop, Tsukuba, Japan, January 2003.

8. Mar 03 Denver Case Study Commercial jet engines sustained severe damage from freezing drizzle at Denver International Airport Commercial jet engines sustained severe damage from freezing drizzle at Denver International Airport Traditional forecasts failed to predict fog or supercooled drizzle Traditional forecasts failed to predict fog or supercooled drizzle Radiometric retrievals of relative humidity increased to saturation during the 12 hours prior to onset of fog Radiometric retrievals of relative humidity increased to saturation during the 12 hours prior to onset of fog Accurate fog forecast and detection of supercooled fog onset was possible with radiometric RH and cloud liquid soundings Accurate fog forecast and detection of supercooled fog onset was possible with radiometric RH and cloud liquid soundings

9. Radiometric retrievals at Boulder showing arrival of cold upslope air below 1 km height and associated condensation of supercooled fog.

10. Radiometric RH retrievals (blue) increasing from 30% to saturation below 1000 m height from 00 to 12 UTC on 4 Mar 03 at Boulder. The 00 and 12 UTC Denver radiosondes are shown for comparison (red).

11. Radiometric retrievals at Boulder (red) compared with radiosonde soundings at Denver (blue) during arrival of upslope and supercooled fog. [Start slide show to animate]

12. Conclusions Conventional numerical forecasts did not predict fog conditions which caused airport closing Conventional numerical forecasts did not predict fog conditions which caused airport closing Radiometric retrievals showed steady RH increase to saturation for 10 hours prior to fog onset Radiometric retrievals showed steady RH increase to saturation for 10 hours prior to fog onset Accurate numerical fog forecast was obtained when radiometric soundings were assimilated Accurate numerical fog forecast was obtained when radiometric soundings were assimilated Time series of RH and cloud liquid soundings can help forecasters predict timing and severity of fog conditions. Time series of RH and cloud liquid soundings can help forecasters predict timing and severity of fog conditions.