Applying Traditional and Modern Fog Forecasting Techniques using AWIPS

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Applying Fog Forecasting Techniques Using
AWIPS and the Internet
By Rob Cox
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Overview

• Statistics
• Fog Types
• Ingredients for Radiation/Advection Fog
• Forecasting Techniques
• Summary

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Why do we need good fog forecasts?

• 1981-1989, 6000 deaths nationwide due to fog
• Average 600 deaths nationwide per year (Source
  Goodwin 2002)
• 4 major fog related accidents in 1990-1991
  involved 240 vehicles, causing 21 fatalities
• January 12, 2005 Dense Fog caused a 32 car
  pile-up on Indiana Toll road

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Aviation Folks Would Appreciate It

• 1995-2000 NTSB reported 63 of all weather
  related aircraft fatalities were due to low
  IFR/Fog situations. (Pearson, 2002)
• Results in delayed operations and cost airlines
  millions of dollars each year.
• A large majority of these accidents are due to
  pilot error.

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Types of Fog in Central Plains

• Radiation fog common type of fog produced over a
  land area when radiational cooling reduces the
  air temperature to its dewpoint.
• Advection fog- A type of fog caused by the
  advection of moist/warm air over a cold surface,
  and cools the airmass to below its dewpoint?
• Hybrid fog -A Hybrid fog situation involves
  radiation and advection processes.

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Ingredients for Radiation Fog

• Clear Skies
• Ample Boundary Layer Moisture
• Lack of Turbulence
• This is all fine and good, but are these the only
  ingredients?

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• YES

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Battle of the Fluxes at Night
Sensible Heat Flux
Latent Heat Flux
Net Radiation
Recall Rn - G SH LH
Ground Heat Flux
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Ingredients for Radiation Fog

• Ground Heat Flux- Flow of heat into or out of
  soil. Factors that affect this are porosity,
  moisture content and organic matter.
• Sensible Heat Flux- change of heat to a surface
  without a phase change. For example, mixing,
  advection, and convection.
• Latent Heat Flux- change of heat to a surface due
  to a phase change. For example, Evaporation,
  Condensation etc..

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How latent heat affects fog development

• Deposition/Dewfall-Can delay onset up to 4 hours.
  
• A. Reduces Surface Humidity and increases
  temperature through latent heat.
• B. Takes place in Surface Ridges where more
  subsidence is present.
• C. Often results in patchy fog events,
  especially if ground is dry and warm.

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January 3, 2006 SGF
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Other factors involved

• Fog Top Cooling -Good drying above fog top
  inversion
• Stratus Build Down -Dependent on Soil Conditions
  and Fog Top Cooling

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Forecasting Radiation Fog

• Tools needed
• UPS technique - Bufkit, MR on VB
• Soil type - Clay, Silt, Sand etc
• Soil Conditions -, Cold, wet
• Lack of vertical motion/subsidence in the
  Isentropic surface just above the boundary layer.

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AGOTOP/OK MesonetSoil Temperatures
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Isentropic Adiabatic Omega(Neutral Values in
Pale Green)
January 3, 2006
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Forecasting Radiation Fog

• 4. Sfc. Obs/MSLP-East of High Pressure
• 5. Boundary Layer RH- Greater than 90
• 6. Enhanced Satellite Imagery
• 7. Raobs
• 8. Frontal/Outflow Boundaries

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Forecasting Advection Fog

• UPS

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Forecasting Advection Fog

• Tools Needed
• Often Develops East of Low Pressure and along and
  ahead of a tight thermal/moist gradient. (Sfc.
  Chart)
• Moisture Transport Vectors
• Profilers/Signal Power
• Model Soundings
• Tends to Increase Sensible Heat

(www.profiler.noaa.gov)
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Dense Fog
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Moisture Tranpsort Vectors (January 12, 2005)
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January 12, 2005
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Summary

• How do we predict fog more accurately at WFO
  level? You need to know or have access to the
  following
• Soil types-Clay/Sand/Silt etc
• Role of heat fluxes-Ground/Latent etc
• UPS technique-(Bufkit) using a High vertical
  resolution model- for example Workstation WRF,
  Ruc20
• Isentropic Adiabatic Omega
• Raw data analysis-Raobs/Sfc