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A. The History Behind Weather Maps
Weather maps can display current observations and numerical model output. Meteorologists frequently access this data on their computer workstations.
The weather map was not developed until the telegraph was working. Back in the 1870's, the first weather map came to be. At that time, the government meteorologists worked for the US Army Signal Service. Later, this department became the Weather Bureau and now it is known as the National Weather Service.
In order to make a weather map, stations from around the country would take observations. Meteorologists recorded temperature, wind speed and direction, and pressure. This data was then sent to one location, Washington, DC, where it was analyzed by hand.
Because a large part of the US was not well populated in the late 1800s and early 1900s, the weather maps of the day were missing observations from most of the central Plains states. Also, meteorologists did not always understand what the maps they were analyzing meant. Many of the theories used today in forecasting had not yet been developed.
B. How Do Weather Maps Help Meteorologists?
The weather map is the most valuable tool that the meteorologist uses to forecast the weather. Without this tool, it would be very hard to predict what the weather was going to do. Weather maps summarize what is happening in the atmosphere at a certain time, and it would be very difficult to predict changes in the weather without these maps.
By looking at weather maps from different heights in the atmosphere, a meteorologist can make a three-dimensional picture, in their heads, of what is happening in the atmosphere. They can tell whether a particular area has high or low pressure, whether it may rain, and many other things just by looking at a weather map.
Today, weather observations are taken from thousands of locations. This data is then sent to Washington, DC where it is analyzed. Computers are the main tool creating weather maps since they can handle large amounts of data quickly. Forecasts have become much more accurate since meteorologists have better weather maps than in the past.
C. Analyze a Map on Your Own
The following are a few sources of current weather maps. Sometimes a site may be down or experiencing data losses. In such a case, try another site listed. This is not meant to be an exhaustive list. These are provided for your convenience. Updated April 24, 2003
- Ohio State University: http://asp1.sbs.ohio-state.edu/ (Click on "Current Weather" and choose your map)
- NCAR: http://www.rap.ucar.edu/weather/surface/ (Pick your regional plot.)
- UNISYS: http://weather.unisys.com/surface/sfc_map.html
- College of DuPage: http://weather.cod.edu/analysis/analysis.sfcplots.html
These weather maps are similar to those used by meteorologists. On the Ohio State maps, the blue lines are cold fronts and the red ones are warm fronts. The NOAA map also has warm and cold fronts shown, but in black. Cold fronts have triangles along the line indicating the position of the front and warm fronts have half-circles.
On all maps, the white circles with lines coming out of them are wind barbs. They point towards the direction from which the wind is coming from. The number above and on the right of the wind barbs tell about the atmospheric pressure at that location. Large numbers mean there is high pressure and smaller numbers mean there is low pressure. The maximum is symbolized with a blue H (Ohio State map) while the minimum has a red L. Differences between high and low pressure causes wind, and air moves counter-clockwise around areas of low pressure and clockwise around areas of high pressure. Using these facts, analyze one of these maps on your own.
- Where are the areas with the highest pressure? __________
- Where are the areas with the lowest pressure? __________
- Which direction is the wind blowing from in Oklahoma? ________
- Which direction is the wind blowing from in Michigan? _________
