Fronts

  1. First pass frontal analysis on chart showing 1000-500 thickness and surface isobars. Shown in inset.

    • Since fronts are defined as the surface expressions of boundaries between deep air masses with significant temperature differences, as a first guess they can be found on the warm air side of the packing of, for example, 500 mb height (crudest), 1000-500 mb thickness (crude) fields
    • The relation of surface winds to thickness contours allows one to assess temperature advection, and to make a better estimate of both the location and type of surface fronts (Note: In reality, finding surface fronts requires a careful analysis of actual temperature fields, instead of the layer mean temperatures inferred from thickness or height maps. Here is the NCEP analysis; note that the general position of and type of fronts for the eastern two thirds of the US was well "guessed", but the complications associated with the actual wind and temperatures in southwest TX made our "first guess" poor there)
  2. Sketch frontal positions in lightly on acetate on the basis of the steps above and your first guess in (1)
  3. Now draw isobars to fit the frontal position.
  4. Once frontal positions are finalized, make sure isobars KINK AWAY from low pressure, as shown in class.
  5. Regions of surface low pressure not associated with fronts. Can often be associated with significant bad weather. Indicate persistant troughlines with dashed black or brown line.
  6. Specialized Troughs have their own symbol set as discussed in class. (e.g., Dry Line; outflow boundaries).