Classical Surface Analysis
Goal of weather map analysis: “After careful consideration of their representativeness
and reliability, all available meteorological data must be fitted into the most probable
system of ideal and modified three-dimensional tropospheric models. Analysis is a
diagnosis and a synthesis of the data guided by adhering to geometrical, kinematic,
dynamic and thermodynamic consistency”
From Dynamic Meteorology and Weather Forecasting, 1957, by C.L. Godske, T.
Bergeron, J. Bjerknes, and R.C. Bundgaard, p. 651.
The following is the sequence of steps recommended by the Norwegian Bergen School
for the analysis of the surface weather map:
1. Location of air masses
Warm and cold air masses are formed in source regions located away from the active
storm tracks. For example, maritime tropical air masses are associated with the
subtropical highs. These are warm highs which strengthen with height. Polar and
arctic air masses are high pressure areas which usually form over northern continental
regions due to radiational cooling and dynamical processes aloft (anticyclonic vorticity
advection; cold-air advection). These cold highs weaken with height and may actually
evolve into a cold low aloft. Air masses are characterized by relatively homogeneous
properties but when they move from their source regions, baroclinic zones (fronts) may
form at their leading edges and significant weather may result.
When a warm air mass moves poleward from its source region, it is cooled from below,
thus becoming more stable with time (∂θ/∂z increases). It is characterized by stratiform
clouds, fog and drizzle. When a cold air mass moves equatorward from its source
region, it is warmed from below and is destabilized with time (∂θ/∂z decreases). Its
leading edge (the cold front) is associated with showers and thunderstorms, followed by
fair weather as the air mass center moves in.
Analysts typically use temperature, dew point temperature, visibility, cloud types, and
current and past weather to locate and identify air masses. Some general guidelines
have been formed to locate air mass boundaries which should be modified for local
climatology. The classical rules are: that T≥65˚F, Td≥60˚F represents tropical
(maritime) air while arctic air is characterized by T<40˚F, Td< 32˚F.
2. Cloud and weather analysis
Overcast and clear regions are located and indicated. Cloud types and ceilings should
be noted. Precipitation occurrence and type should be identified. This is done by
shading areas of fog, drizzle, rain, ice pellets and snow and using symbols to indicate
showers, past and current thunderstorms, dust, etc. See handouts for proper symbols
and color conventions.
