The term synoptic means "generalized," or "taking a view of the whole." Synoptic weather forecasting is done by assembling weather maps of large regions from observed and reported data at numerous stations (station models). The defining tool of synoptic forecasting is the weather map.
Synoptic forecasting evolved before computers were available to analyze weather data in high detail. A meteorologist might look at a sequence of weather maps showing conditions in the United States at intervals of a few hours, and deduce from it the conditions likely to exist for various locations a few hours, a day, or two days into the future. Fig. 3-9 is a simplified example of such a map, showing a high-pressure system (H) centered in the western United States, and a low-pressure system (L) centered in the southeast. Two hypothetical towns, Plainsboro in the Midwest and Surfsburg on the East Coast, are shown. The arcs with arrowheads represent the general wind circulation around the weather systems. The heavy, dashed line shows the position of the jet stream.
At the temperate latitudes, major weather systems tend to move generally from west-to-east at 20 to 30 kt. Based on this, even a meteorologist can come to the reasonable conclusion that the weather should be improving in Plainsboro and deteriorating in Surfsburg over the next 24 hours. High-pressure systems are usually associated with fair and warm weather, while low-pressure systems are associated with foul weather.
More detailed information can be obtained from Fig. 3-9 if we know the time of year. If it is January, Plainsboro might expect to see cool and clear weather for the next day or two, while Surfsburg can expect high winds and rain, fol-
lowed by cold weather and perhaps some snow. We would have to know the temperatures at numerous stations throughout the U.S. to get a better idea about this. If it is April, Plainsboro might enjoy a couple of warm, sunny days, while Surfsburg would brace for the possibility of severe thunderstorms or tornadoes. Again, the intensity of the weather systems, and the temperatures associated with them, would have to be determined by looking at the station models for numerous locations across the country.
Do you get the idea that synoptic forecasting is as much an art as a science? If so, you're right. Meteorologists in the early part of the 20th century relied on their experience and intuition, as well as on mathematics and physics. But that began to change in the 1960s and 1970s as computers became more available and more powerful.
What can the town of Plainsboro and Surfsburg expect three days after the existence of conditions shown in Fig. 3-9? After a week? After two weeks?
After three days, it's possible that the high-pressure system out west will have made its way to Surfsburg, giving them improved weather. But we can't be sure about this, based on the map alone. The storm system currently bearing down on Surfsburg will likely have moved out to sea. We have little idea of what to expect in Plainsboro after three days, because we must know what is coming in from the Pacific, and we must also know whether the high-pressure system out West will move along or remain fixed. The data in Fig. 3-9 is not enough to give us a good idea, much less a precise forecast, for conditions in either town after a week or two weeks have passed.
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