Forecasting Radiation Fog

Forecasting Radiation Fog
At the end of the module you should be able to do the following things: With Regard to the Preconditioning Environment: • Identify key conditions and ingredients necessary for development of radiation fog • Discriminate between large-scale low-level environments that are favorable and unfavorable for development of radiation fog • Describe the sequence of key surface and boundary layer processes that prepare the low-level environment for development of radiation fog • Demonstrate an understanding of how surface cooling dries the micro-boundary layer and prevents low-level condensation from being deposited onto the surface • Rank various surface and surface cover types in terms of the relative speed with which low-level air in contact with them will reach saturation With Regard to Initiation and Growth: • Identify levels at which radiative cooling is most active at various stages of the fog initiation and growth process • Demonstrate an understanding of the effects that various condensation nuclei types and concentrations have on fog formation • Sequence the key processes and events that occur during formation of a layer of radiation fog • Demonstrate an understanding of how the fog-top inversion is created by the fog itself • Demonstrate an understanding of influences that heat flux from the surface have on a fog layer during its initiation and growth With Regard to Maintenance Phase: • Describe key processes that balance one another to allow a fog layer to maintain a relatively constant depth • Identify conditions in and above a fog-top layer that support continued condensate production • Identify conditions in and above a fog-top layer that restrict further deepening • Demonstrate an understanding of the effects that various condensation nuclei types and concentrations have on fog maintenance • Demonstrate an understanding of the effects that introduction of an overlying cloud layer have on a mature fog layer at the surface • Demonstrate an understanding of influences that heat flux from the surface have on a mature fog layer • Identify the typical level of a fog-top inversion • Demonstrate an understanding of how the fog-top inversion is maintained by various processes at and above the top of the fog layer With Regard to Dissipation Phase: • Identify key processes that contribute to the dissipation of a fog layer • Apply a droplet settling rate calculation to predict the time required for a given depth of fog layer to settle to the ground in the absence of any new condensate production • Demonstrate an understanding of how radiative heating contributes to dissipation of a fog layer • Demonstrate an understanding of how turbulent mixing contributes to dissipation of a fog layer • Demonstrate an understanding of how changes in low-level winds can contribute to dissipation of a fog layer • Demonstrate an understanding of how introduction of an overlying cloud layer can contribute to dissipation of a fog layer With Regard to Detecting Fog: • Identify surface observations that show atmospheric conditions conducive to radiation fog • Identify soundings that show atmospheric conditions conducive to radiation fog • Identify fog in satellite images • Describe the limitations of infrared satellite images for detecting radiation fog With Regard to Forecasting Fog: • Describe the diurnal cycle of radiation fog occurrence • Demonstrate and understanding of the strong seasonal dependence of radiation fog occurrence in at least two localities • Describe which forecast products best show the atmospheric conditions conducive to radiation fog • Describe the limitations of numerical forecast models in predicting radiation fog