Assembling thousands of complex maps per hour sounds like a job for a supercomputer, but the Web server behind MyWxmap is a so-called Beowulf cluster of 32 ordinary desktop computers running Linux. The cluster is the first operational Beowulf system deployed in the Navy, Ravid said.

Most of Fleet Numerical's data-rich weather forecasts and weather maps are geared to Defense Department users, because its primary mission is to forecast for the armed forces.

Whereas the civilian-oriented National Weather Service is mostly concerned about storms in and near U.S. territory, Fleet Numerical must predict global weather because of DOD's worldwide operations.

Authorized users at DOD, some civilian agencies and a few research centers can specify the types of data they want to see for a chosen region.

Selected views

Fleet Numerical makes available public images and data for some fixed areas, such as the continental United States, but not the world's hot spots.

The calculations behind the MyWxmap charts run on Fleet Numerical's supercomputers, such as a 512-processor SGI Origin 3000, which ranks among the world's 200 fastest.

To determine what to provide in MyWxmap, members of Ravid's group studied the weather information people consult on the Web. They found that about 20 percent of weather data consumers are meteorological experts and researchers. The rest are nonspecialists, so Fleet Numerical geared parts of MyWxmap toward them, Ravid said.

The public MyWxmap charts have many details not found on consumer-oriented weather maps, but they also require users to have some knowledge of what they're seeking.

A consumer who clicks the Public Charts button on Fleet Numerical's public Web site, at www.fnoc.navy.mil/PUBLIC/, must first select a predefined region of the globe.

The Navy's main weather simulation software'the Navy Operational Global Atmospheric Prediction System, or NOGAPS'generates most of the models, but several regions also have forecasts from the Coupled Ocean/Atmosphere Mesoscale Prediction System, or COAMPS, which takes sea-surface temperatures into account.

MyWxmap uses more technical terms than consumer weather charts. Wind barbs, which look like small stick flags, show the direction and speed of wind in knots. Isotachs are lines that connect points of equal wind speed. Fleet Numerical measures atmospheric pressure in hectopascals, abbreviated hPa, which are the same as millibars, Ravid said.

Novice weather buffs who click on the help button see a user manual in another browser window. Fleet Numerical has organized an informal user help group on Microsoft Corp.'s MSN.com service.

Navy meteorologists who give weather guidance to U.S. troops must consult different global models, Ravid said. For a given region and time, a Navy model might work better or worse than that of the National Weather Service or the European Community's similar models.

Carbon-based input

Despite the massive computing horsepower at Fleet Numerical and its civilian counterparts, some weather scenarios still call for human judgment.

'MyWxmap will give [meteorologists] a means to make those choices without having to go to five different places, which is what they have to do now,' Ravid said.

The MyWxmap cluster of 32 750-MHz PCs cost about 10 percent as much as a 32-way server, but it generates up to 150,000 weather charts per hour, Ravid said. Customizing graphical images for MyWxmap is what programmers call an 'embarrassingly parallel problem,' he said.The PCs in the cluster work independently in parallel, all controlled by one computer that doles out the work, much like a factory production manager, Ravid said.

At first, nobody at Fleet Numerical believed that a Beowulf cluster could succeed in such an environment.

'Our technical director chuckled when I brought the proposal to him,' Ravid said. 'I told him, 'This is for real. This technology has already been proven in a couple of applications that NASA's using.' '

NASA's Goddard Space Flight Center pioneered Beowulf clusters in the early 1990s; they quickly became a hot research tool at government and university laboratories.

Ravid received $10,000 to build a prototype with six older PCs before purchasing the 32 PCs for the operational system.

He and his staff compared 32 PCs against a Sun Microsystems Inc. Enterprise 10000 K configuration. They found the cost for similar capacity was $200,000 for the cluster versus $2 million for the latter.

The Beowulf technology also adds fault tolerance, Ravid said. The PC that controls the cluster can tell when one of the CPUs has malfunctioned and can assign its work to another without interruption.

Last fall, the MyWxmap design team received a PostNewsweek Tech Media Government IT agency award for its work.