BRIDGEPORT, W. Va. (WDTV) - Progressive weather patterns move storm systems quickly across the country. Blocking weather patterns keep the weather stagnant over the same locations for prolonged periods of time.
Progressive patterns move weak storm systems across the country in about 2 or 3 days. This is because the jet stream which drives them is typically aligned west to east, with little north to south movement. An east/west jet stream is usually associated with a gradual change in temperature from south to north across the country. These weak temperature differences make for weak storm systems. While there can be a cool down behind these storms, it usually warms up fast, since there is not a lot of cold air associated with the storm in the first place.
The blocking weather pattern often times takes two forms in the U.S. Warm in the west and cold in the east, or the reverse. When the jet stream takes a big turn north, warm air follows it. When it dips far to the south, the cold air follows.
The jet stream is the DIVIDING line between warm and cold air high in the atmosphere. The stronger the jet stream, the bigger the difference in temperature. Usually taking place over a short distance. These differences are reflected lower in the atmosphere as fronts and low pressure systems.
So, putting these together. Jet stream far to the north = warmer air farther north. Jet stream farther south = colder air farther south. This makes for a breeding ground for storm systems. These form in and around where the jet stream dips south. In this area, the counter-clockwise flow of the jet is what forms the counter-clockwise flow of the low pressure system. This means first, colder air, second, more clouds, and third, precipitation. This time of year that is rain or snow.
The other half of the blocking pattern is associated with high pressure and the northern reaching jet stream. The flow of the jet is clockwise and leads to high pressure. High pressure means sinking air, clearing skies, and often sunshine. Combine that with the northward flow of the warm air and the weather if often 'nice' under the high pressure half of the pattern.