Fog frequently forms in response to dynamically forced changes in the boundary layer. This module examines dynamically forced fog in the coastal and marine environment, focusing on advection fog, steam fog, and west coast type fog. The focus of the module is on the boundary layer evolution of air parcels as they traverse trajectories over land and water. The module also examines mesoscale effects that impact the distribution of fog and low-level stratus over short distances. A general discussion of forecast products and methodologies concludes the module.
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After completing this module, the learner should be able to do the following things:
With regard to the general features of dynamically forced fog and stratus:
• Describe the differences in boundary layer characteristics and evolution for advection, West Coast, and steam fog in a marine environment
• Describe the differences in synoptic environments for advection, West Coast, and steam fog in a marine environment
• Describe the relationship of sea surface temperature to fog formation for advection, West Coast, and steam fog in a marine environment
With regard to advection fog:
• Describe the general synoptic environment that is conducive to fog formation
• List at least 2 ways that subtropical high-pressure systems contribute to the formation of advection fog
• Describe the evolution of the boundary layer along an air parcel trajectory that leads to advection fog
• Describe how sea surface temperature changes along an air parcel trajectory that leads to advection fog
• Recall the origins of strong sea surface temperature gradients
• On a world map, identify areas prone to advection fog
• Recall the seasonality of advection fog
With regard to West Coast fog and low stratus:
• Describe the general synoptic environment that is conducive to fog formation
• List at least 2 ways that subtropical high-pressure systems contribute to the formation of West Coast fog and low stratus
• Describe the evolution of the boundary layer along an air parcel trajectory that leads to West Coast fog and low stratus
• List at least 2 ways that the boundary layer cools to saturation in a West Coast fog/stratus event.
• Recall the role of upwelling in the formation of West Coast fog and low stratus
• On a world map, identify areas prone to West Coast fog and low stratus
• Recall the seasonality of West Coast fog and low stratus
With regard to steam fog:
• Describe the general synoptic environment that is conducive to fog formation
• Describe the characteristics and evolution of the boundary layer along an air parcel trajectory that leads to steam fog
• On a world map, identify areas prone to steam fog
• Recall the seasonality of steam fog events
With regard to mesoscale influences upon dynamically forced fog:
• Describe the effects of coastal topography in fog formation
• Describe how coastal jets affect fog formation and dissipation
• Describe how sea breezes affect fog formation and dissipation
• Describe the impact of local variations in sea surface temperature on fog formation and dissipation
With regard to forecasting dynamically forced fog:
• Describe the general approach to forecasting fog
• List at least 4 critical atmospheric fields to monitor in plan view when forecasting fog
• List at least 4 critical atmospheric fields to monitor in vertical profiles when forecasting fog
• Describe the limitations of NWP models in fog forecasting
