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.
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.
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
troughs in the MSLP field
Fronts are often found in pressure troughs.
pressure tendencies
Look for pressure rises behind cold fronts, falls ahead of warm fronts
moisture discontinuity
Drier air behind cold front, moist air ahead of front
upper-air charts
Look especially for 850 mb temperature gradients.
1000-500 mb thickness
Thickness is proportional to the mean temperature in the layer.
current weather
Light to moderate stable precipitation ahead of warm fronts; convection ahead of cold fronts.
time continuity
How is the temperature gradient changing in time?
local/topographic effects
Wind blowing through river valleys, etc.