Mid-latitude Cyclone Storms

rains without tornadoes. Extremely cold air masses in winter give rise to Artic air often preceded by snowstorms.

The warm fronts are gentler in nature when they occur as the warm air simply slides over the cooler and denser air that has less power overall. You can feel the transition more gradually with cirrostratus clouds seen rather than cumulonimbus clouds. Snowflakes and gray skies are seen in the wintertime as the front approaches. A low pressure system is still generated with cold air initially beneath warm air. You will still feel coldness between the two air masses until the warm air overtakes the colder air. The worst weather is when the front goes through. Snow will become freezing rain and then rain will occur. It might be foggy until the front passes.

Occluded fronts are those where a cold front finally catches up to a warmer front. You might see airmasses to be cold, warm, and finally colder again. These are seen as purple line with triangles and half circles along the line. Because of the Coriolis effect, the front lines will curve with a low in the middle. Figure 36 shows these fronts. Remember that there is a low pressure system behind these fronts and not a high pressure system. There is very bad weather behind this front. Look for these along the Pacific coastline.

MID-LATITUDE CYCLONE STORMS

Mid-latitude cyclones are of course seen in the middle latitudes, between 30 and 55 degrees North in the northern latitudes. Like all storm systems, these circle around low pressure systems but, in no way are these same thing tropical storm or hurricane. The differences are twofold. First, they are found in the mid-latitudes and not in the tropical areas of the world. Second, they are much larger than hurricanes and tropical storms.

How do these mid-latitude cyclones form? They seem to occur whenever there is much colder and drier air to the north and moisture warmer air and the South. Using the initials for air masses, you would label these a joining of CP and MT air masses. Due to the Coriolis effect, this boundary will begin to circulate in a counterclockwise direction. Warm air is drawn further up and cold air is pulled down from the north. This is called the process of cyclogenesis.

Because this is a circulating low-pressure system, you can imagine that all of the air is sucked inward similar to making a whirlpool in a bathtub or pool. While water will circulate going down a drain, air cannot do this so instead it rises upward. The upperlevel winds then take this cyclone and move it eastward. Ultimately, if the upper-level winds cannot cooperate, the cyclone will decay.

However, if the upper-level winds are more favorable, these cyclones will suck up warm air and bring down cold air. As the warm and humid air rises, a low-pressure system becomes deeper ahead of the cyclone. Behind the cyclone, the cold air will just fill in as it drops down for toward the south. As this air fills in, the cyclone simply gets pushed along to the east.

When a mid-latitude cyclone is completely formed, you will see small mini fronts radiating out from it. A mature cyclone has a deep low-pressure system in the middle and an occluded front developing whenever a cold front catches up to a warm front. These occluded fronts are usually assigned that the cyclone is about to decay. They lose their strength and break up.

There are a few locations in North America where you will see these mid-latitude cyclones. They are commonly seen, for example, just east of the Rockies which would be the lee side. You probably know them by the names Alberta clippers or Colorado lows. Alberta clippers move rapidly but have little precipitation, largely because they are dry. Colorado lows have a large differential between the warm air mass and the cold air mass, commonly bringing air up from the Gulf of Mexico. These are associated with very bad weather such as sleet, heavy snows, strong thunderstorms, and blizzards.

You may also see these on the East Coast of the United States. Gulf Lows are seen in the south east and are associated with a great deal of rain or snow. This is because they are so close to a large body of water. The most severe storms of all are called Nor'easter's or bomb cyclones. These are so strong because they are formed with waters from the Gulf Coast as well as the colder waters of the Atlantic Ocean. These are extremely wet and have very strong low-pressure systems associated with them. The wind is intense, with these types of cyclones starting fairly quickly.

In terms of storm tracks, Alberta clippers start out as low-pressure systems in the Gulf of Alaska and move along the border between Canada and United States. Colorado lows will develop near Colorado and travel up toward the Great Lakes. Gulf Lows begin in Louisiana and travel to the Northeast but do not spend much time over the Gulf of Mexico. Hatteras lows or nor'easter's begin in the Gulf of Mexico, picking up more moisture in the Atlantic Ocean, and then travel along the eastern seaboard of the United States.