TRAJECTORY PATHS C AND D (ANTI-CYCLONIC). The weather conditions ex-perienced over the central United States under the influence of trajectories similar to C and D (fig. 4-1-5) are quite different. Unusually smooth flying conditions are found in this region, except near the surface where a turbulence layer results in a steep lapse rate and some bumpiness. Low stratus or stratocumulus clouds may form at the top of the turbulence layer. As the cold air stagnates and subsides under the influence of the anticyclonic trajectory, marked haze layers develop indicating the presence of sub-sidence inversions. The surface visibility also deteriorates because of an accumulation of smoke and dust as the air stagnates and subsides. This is especially noticeable during the early morning hours when the stability in the surface layers is most pronounced. In the afternoon, when surface heating has reached a maximum, the visibility usually improves because of the steep lapse rate and resultant turbulence.

Movement of cPk and cAk air westward over the Rocky Mountains to the Pacific coast is in-frequent. However, when successive outbreaks of cold air build up a deep layer of cP air on the eastern slopes of the Rocky Mountains, relatively cold air can flow toward the Pacific coast.

TRAJECTORY PATH E. When the trajec-tory of the cold air is similar to E in figure 4-1-5, rather mild temperatures and low humidities result on the Pacific coast because adiabatic warming of the air flowing down the mountain slopes pro-duces clear skies and good visibility.

TRAJECTORY PATHS F AND G. oc-casionally, the trajectory passes out over the Pacific Ocean (see fig. 4-1-5). The air then arrives over central and southern California as cold, connectively unstable air. This type is characterized by squalls and showers, cumulus and cumulonimbus clouds, visibility of 1 to 5 miles during squalls and showers, and snow even as far south as southern California.

Figure 4-1-7.cP air moving over the Great Lakes (winter). 

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