5/1/2023 0 Comments Orographic lifing diagram![]() After the air passes across the mountain range, it will begin to sink and dry out, and in some cases greatly warm the surrounding air. As the air rises, it begins to cool and condense, and depending on how moist the air mass is, showers or thunderstorms could form. Since the air has nowhere to go but up, it is forced up the side of the mountains. When air moves across the Ohio and Tennessee valleys, it encounters the Appalachian Mountains. Orographic lift in the Southeast occurs mainly along the Appalachian Mountains. However, if unstable air is lifted through one of the mechanisms below, it can cause the explosive development of thunderstorms and flooding rains. In stable conditions, the vertical movement of air will be smooth and is not likely to cause deep convection like thunderstorms. The upward motion of air can lead to the formation of clouds and precipitation if there is sufficient moisture to reach condensation as the air cools while moving up. ![]() I should already be familiar with: Fronts, Stability, Convergence and Divergence, ConvectionĪir can move vertically for several reasons covered below. Why do I care? Lifting mechanisms are important for the formation of clouds and rain (in combination with moisture and instability). In this topic we cover orographic lift, frontal lift, convergence, and convective lift. This is a banner cloud and should not be confused with snow blown from the crest or peak.Lifting mechanisms are forms of lift that cause air to rise. When the wind is strong, the orographic clouds formed near the summit may be observed streaming away from the mountain on the leeward side. Orographic cloud in stable conditions and low moisture windward Under drier conditions, waves may be present without cap clouds.įigure 4. It is important to remember that their absence does not mean that waves are absent. Sometimes, the clouds resemble a bank or wall that follows mountain contours. In the case of a mountain barrier, observed from the leeward side, cap clouds indicate likely wave activity downstream. These clouds give little or no precipitation. In the case of an isolated mountain, orographic clouds often have the form of a collar, surrounding the mountain or that of a cap covering the peak (Figure 4), both of which are fairly symmetrical. This process, referred to as orographic enhancement of precipitation, requires specific synoptic conditions not related to topography.Ĭlouds thin out and dissipate on the leeward side, where the relief causes descending motion and the precipitation is notably less ( rain shadow). Quite often, heavy orographic precipitation occurs on the upwind side of the barrier, particularly for barriers located near the sea. Precipitation may start or increase in intensity. The clouds become denser, the size and concentration of water droplets or ice particles increase and frequently develop greater vertical extent. Therefore, hilly areas are often cloudier than nearby lower land.įigure 3. Orographic cloud in unstable conditions and high moisture windwardĮxisting clouds arriving over mountainous or hilly areas, situated at heights comparable with that of the obstacle, may change in shape and structure as a result of the topography. Air also rises up a slope due to daytime heating so both orographic and thermal lifting often work together to produce tall, vertically developed Cumulus clouds (Figure 3). ![]() The type of cloud that forms depends on the air stability and moisture content. Orographic cloud in stable conditions and high moisture windward If the flow is sufficiently humid, clouds form on the windward side of mountains and are called orographic clouds (Figure 2).įigure 2. As airflow encounters a mountain or hill, it is forced to rise this is referred to as orographic lift.
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