![]() ![]() In the southeast corner of the state, temperatures were in the 80s. For example, check out the change in temperature just in the state of Kansas ( outlined in the black box). Such a large temperature gradient marks a contrast between very warm air and colder air. For example, the analysis of surface isotherms from 19Z on shows a very large temperature gradient (tight packing of isotherms) stretching all the way from the Southwestern U.S. Turning our attention to temperature, tightly packed isotherms represent large horizontal changes in temperature over a relatively short distance (that is, a large temperature gradient). There's not a single isobar in California or Nevada, and overall isobars are packed very loosely in the West, so pressure changes very little over the entire region. On the flip side, for an example of a small pressure gradient, look at the western United States on the map above. This case was no exception! This area of low pressure was dubbed " The Blizzard of 2017" and winds along the coast in Massachusetts gusted to more than 70 miles per hour. As you'll learn in later in the course, tight packings of isobars (large pressure gradients) correspond to strong surface winds. and eastern Canada, indicating a large pressure gradient over this region (relatively large pressure changes over a short distance). Note the tight packing of isobars over the northeastern U.S. Check out the 06Z analysis of sea-level pressure on Ma(below), which shows a powerful low-pressure system along the New England Coast. Now let's take what we've learned from topographical maps and generalize it to weather maps. ![]() Thus, a small gradient, which marks little change in elevation over a relatively short horizontal distance (fairly flat terrain), corresponds to a loose packing of contours. Meanwhile, the "packing" of contours of constant elevation is rather loose where the terrain is flatter. Thus, a large gradient on a topographical map, which marks a large change in elevation over a relatively short horizontal distance (steep terrain), corresponds to a tight packing of contours. Remember that the contours of constant elevation are packed close together in areas where the elevation changes rapidly over short distances (like near the mountain summits). How do we distinguish between a large and small gradient on a topographical map? Let's return to the video showing the virtual topography of Hawaii ( video transcript) you saw earlier. Similarly, a small gradient means that the elevation of the road changes very little with distance (the road is relatively flat). In other words, you're driving on a steep hill. What does that mean in practical terms? For the mountain road to have a large gradient, the elevation of the road must change relatively rapidly over a short traveling distance. Driving to the summit of the beautiful mountains in central Pennsylvania, motorists are greeted by signs that warn of "steep grades" ahead, which refers to large gradients. Zones where weather variables have large changes are often zones of active weather, so meteorologists like to keep tabs on areas with so-called "large gradients." Tuck this idea away, as the importance of gradients will come back again and again in our studies of meteorology.īut, to start us off in our discussions of gradients, let's return to the example of elevation. The change in a variable over a certain distance is called the gradient, and gradients are very important in meteorology. Similarly, maps of isobars allow meteorologists to find areas of high and low pressure, and see how pressure changes over certain areas. Maps of isotherms allow meteorologists to identify regions of warm and cold air, as well as how temperatures change over certain areas. ![]() In other words, contour maps make it easy for meteorologists to see how a weather variable (like temperature or pressure) is changing over a large area. ![]() You can see the total amount of snow accumulated in the past days or use the animation to see each 6 hour interval separately.Besides allowing meteorologists to estimate values of weather variables at specific points, contour maps are also useful tools that help meteorologists to see patterns in the data. The snow maps can be animated to show forecasts for snow, freezing level, temperature and wind as well as current weather conditions in ski resorts. Choose a snow map from the list of countries and regions below. ![]()
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