Extratropical Cyclones Forming East of the Rocky Mountains

Online 10.3: An Upper-Level Cyclone Crosses the Rockies 300 mb: A sequence of 300mb heights and winds shows the evolution of a trough moving onshore from the Pacific across the Rocky Mountains. An upper level low develops over Arizona and is evident as the trough migrates eastward. White contours are height of the 300 mb surface (m), white arrows are wind vectors indicating wind direction and speed (length of arrow), color coding is wind speed at the 300 mb level in knots.