10.10. Drawing Fronts#

Identifying fronts is not a trivial task, yet they are fundamental parts of our cyclone model since the time of Bjerknes and Solberg [1922]. Therefore, it is important to identify and correctly analyze the location of fronts at the surface. There are times that a front will practically jump off the map, but more often than not it will take time to discern the actual location of a front. Sanders and Doswell [1995] document well the difficulty of identifying fronts. For a given case even experienced meteorologists will often disagree with the placement of fronts. The following are some key factors to consider when attempting to locate fronts.

  1. strong temperature gradients

    • Fronts generally lie on the warm side of temperature gradients. However, beware of diurnal effects, cloudy vs. sunny regions, snow cover line, lake effects, etc.

  2. wind shifts

    • Winds normally veer with a frontal passage: cold fronts - S ahead, NW behind; warm fronts - SE-NE ahead, SE-SW behind, stationary fronts – winds parallel to temperature gradient

  3. troughs in the MSLP field

    • Fronts are often found in pressure troughs.

  4. pressure tendencies

    • Look for pressure rises behind cold fronts, falls ahead of warm fronts

  5. moisture discontinuity

    • Drier air behind cold front, moist air ahead of front

  6. upper-air charts

    • Look especially for 850 mb temperature gradients.

  7. 1000-500 mb thickness

    • Thickness is proportional to the mean temperature in the layer.

  8. current weather

    • Light to moderate stable precipitation ahead of warm fronts; convection ahead of cold fronts.

  9. time continuity

    • How is the temperature gradient changing in time?

  10. local/topographic effects

    • Wind blowing through river valleys, etc.

BS22

J. Bjerknes and H. S. Solberg. Life cycle of cyclones and the polar front theory of atmospheric circulation. Geofys. Publ., 3:1–18, 1922.

SD95

F. Sanders and C. A. Doswell. A case for detailed surface analysis. Bull. Amer. Meteor. Soc., 76:505–521, 1995.