This is part of the Physical Processes Professional Competency Unit of the Forecasting Low-Altitude Clouds and Fog for Aviation Operations Professional Development Series. West Coast Fog discusses the climatology, physical
processes, and evolution of hot spell fogs along the U.S. West Coast.
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The goal of this training module is to help you increase your understanding of how radiation fog forms, grows, and dissipates. Such understanding, in turn, can help you more efficiently and accurately evaluate the ability of a given atmospheric environment to generate and/or maintain radiation fog.
Performance Objectives
With Regard to Climatology
Basic Level Competencies:
• Identify coastal regions worldwide where (west coast-type) fogs occur
• For each region, state the seasons of highest and lowest frequency
With Regard to the Preconditioning Environment:
Basic Level Competencies:
• Identify typical synoptic-scale patterns associated with preconditioning processes that prepare the coastal environment for fog formation
• List low-level and sea surface conditions that are typically present prior to onset of the fog formation cycle
Advanced Level Competencies:
• Sequence key processes and events that occur during the preconditioning phase
• Demonstrate an understanding of how/why the surface inversion forms as a result of hot dry offshore winds
• Describe* how/why/where coastal upwelling occurs
With Regard to Formation:
Basic Level Competencies:
• Identify typical synoptic-scale pattern transitions associated with the formation phase
• Identify the key processes and events that occur during fog formation.
Advanced Level Competencies:
• Apply rules that describe the relationships between SST, inversion base, LCL, MCL, etc.
With Regard to Growth and Maturity:
Basic Level Competencies:
Describe the continued deepening and horizontal growth of the fog
• State the typical maximum height that the inversion can reach with cloud still extending to the surface
• Describe diurnal cycles (including stratus raising/lowering)
Advanced Level Competencies:
• Demonstrate an understanding of the roles that coastal surges can play
With Regard to Fog Dissipation and/or Stratus formation:
Basic Level Competencies:
• List processes that can result in fog dissipation (advection over land, warmer water, synoptic systems, solar radiation, the start of a new cycle)
• Identify typical synoptic-scale patterns that can destroy fog regimes in MBL
• Sequence the major events that comprise the ~15-day warm season fog cycle in this region
Advanced Level Competencies:
• Describe how the fog erodes upward to form the marine stratus regime that was present prior to fog formation
• State general rule regarding relationship between sun angle and fog dissipation through insolation
• Demonstrate an understanding of how/why dissipation occurs when the MCL reaches the base of the inversion
west coast fog, fog, fog frequency, coastal fog, fog phases, fog life cycle, fog seasonal variation, air-sea temperature difference, haze, fog advection, fog dissipation, fog disruption
