Fog Detection

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Fog Detection Forecasting
Using the the Radiometrics TV/WVP-3000
Temperature, Humidity Cloud Liquid Profiling
Radiometer
April, 2003
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Fog Forecast and Detection thru Radiometric
Profiling

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

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Feb 01 Denver Case Study

• Flights were diverted from Denver International
  Airport for 18 hours during Feb 2001 because of
  fog event
• Traditional forecasts failed to predict 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

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Radiometric retrievals at Boulder showing arrival
of cold upslope air below 500 m height and
associated condensation of supercooled fog.
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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).
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Radiometric retrievals at Boulder (red) compared
with radiosonde soundings at Denver (blue) during
arrival of upslope and supercooled fog. Start
slide show to animate
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UCAR Assimilation Experiment

• 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)
• 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.

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Mar 03 Denver Case Study

• Commercial jet engines sustained severe damage
  from freezing drizzle at Denver International
  Airport
• 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
• Accurate fog forecast and detection of
  supercooled fog onset was possible with
  radiometric RH and cloud liquid soundings

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Radiometric retrievals at Boulder showing arrival
of cold upslope air below 1 km height and
associated condensation of supercooled fog.
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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).
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Radiometric retrievals at Boulder (red) compared
with radiosonde soundings at Denver (blue) during
arrival of upslope and supercooled fog. Start
slide show to animate
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Conclusions

• 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
• 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.