Radiometrics CorporationRadiometrics Corporation 11

Fog Detection & ForecastingFog Detection & Forecasting

Using thethe Radiometrics TV/WVP-3000

Temperature, Humidity & Cloud Liquid Profiling Radiometer

April, 2003

Fog Forecast and Detection Fog Forecast and Detection thruthru

Radiometric Profiling Radiometric Profiling

Airports worldwide need a reliable Airports worldwide need a reliable operational system for fog forecastingoperational system for fog forecasting

Water vapor saturation near the surface Water vapor saturation near the surface is required for condensation of fogis required for condensation of fog

Accurate fog forecast and detection is Accurate fog forecast and detection is possible with radiometric profiling of possible with radiometric profiling of relative humidity and cloud liquidrelative humidity and cloud liquid

Feb ’01 Denver Case StudyFeb ’01 Denver Case Study

Flights were diverted from Denver Flights were diverted from Denver International Airport for 18 hours during International Airport for 18 hours during Feb 2001 because of fog eventFeb 2001 because of fog event

Traditional forecasts failed to predict fogTraditional forecasts failed to predict fog

Radiometric retrievals of relative humidity Radiometric retrievals of relative humidity increased to saturation during the 10 increased to saturation during the 10 hours prior to onset of foghours prior to onset of fog

Accurate fog forecast and detection of Accurate fog forecast and detection of onset was possible with radiometric RH onset was possible with radiometric RH and cloud liquid soundingsand cloud liquid soundings

Radiometric retrievals at Boulder showing arrival of cold upslope air

below 500 m height and associated condensation of supercooled fog.

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).

Radiometric retrievals at Boulder (red) compared with radiosonde

soundings at Denver (blue) during arrival of upslope and supercooled fog. [Start slide show to animate]

UCAR Assimilation ExperimentUCAR Assimilation Experiment Conventional MM5 forecast did not predict Conventional MM5 forecast did not predict

fog in Boulder or Denver on 16 Feb 2001fog in Boulder or Denver on 16 Feb 2001

Radiometric profiles at Boulder were Radiometric profiles at Boulder were assimilated into MM5 at UCAR, using assimilated into MM5 at UCAR, using variational analysis (4DVAR)variational analysis (4DVAR)

Accurate fog forecasts were obtained for Accurate fog forecasts were obtained for Boulder and Denver after assimilation of Boulder and Denver after assimilation of radiometric profiles*radiometric profiles*

*Vandenberghe and Ware, Proceedings International GPS *Vandenberghe and Ware, Proceedings International GPS Meteorology Workshop, Tsukuba, Japan, January 2003.Meteorology Workshop, Tsukuba, Japan, January 2003.

Mar 03 Denver Case StudyMar 03 Denver Case Study

Commercial jet engines sustained severe Commercial jet engines sustained severe damage from freezing drizzle at Denver damage from freezing drizzle at Denver International AirportInternational Airport

Traditional forecasts failed to predict fog Traditional forecasts failed to predict fog or supercooled drizzleor supercooled drizzle

Radiometric retrievals of relative humidity Radiometric retrievals of relative humidity increased to saturation during the 12 increased to saturation during the 12 hours prior to onset of foghours prior to onset of fog

Accurate fog forecast and detection of Accurate fog forecast and detection of supercooled fog onset was possible with supercooled fog onset was possible with radiometric RH and cloud liquid soundingsradiometric RH and cloud liquid soundings

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

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).

Radiometric retrievals at Boulder (red) compared with radiosonde

soundings at Denver (blue) during arrival of upslope and supercooled fog. [Start slide show to animate]

ConclusionsConclusions Conventional numerical forecasts did not Conventional numerical forecasts did not

predict fog conditions which caused predict fog conditions which caused airport closingairport closing

Radiometric retrievals showed steady RH Radiometric retrievals showed steady RH increase to saturation for 10 hours prior increase to saturation for 10 hours prior to fog onsetto fog onset

Accurate numerical fog forecast was Accurate numerical fog forecast was obtained when radiometric soundings obtained when radiometric soundings were assimilatedwere assimilated

Time series of RH and cloud liquid Time series of RH and cloud liquid soundings can help forecasters predict soundings can help forecasters predict timing and severity of fog conditions.timing and severity of fog conditions.