What is the pattern of the westerlies?
How is the pattern evolving? What is the pattern of the westerlies? To answer this question, you should check the animated hemispheric 500 mb height and animated satellite imagery to determine the upper air flow pattern. The hemispheric 500 mb height analyses and prognoses will show the migratory troughs and ridges that are being guided by the long wave pattern. How is the pattern evolving? The troughs and ridges in the westerlies will either be stationary, retrogressing, or progressing. A stationary pattern is one where the long waves remain in virtually the same place over several days or longer. Progressive patterns are those in which the long waves evolve from west to east. If the system is retrogressive, the long waves undergo a discontinuous east to west movement whereby an existing long wave trough weakens and moves eastward as the short wave trough, while an upstream shortwave strongly deepens, developing into a stationary long wave trough west of the original long wave positio
