• National Center for Atmospheric Research and the University Corporation for Atmospheric Research (www.ucar.edu) —a collaborative effort of research centers, universities, and weather offices around the United States, this site provides numerous real-time and forecast weather products and graphics. 

• Aviation Digital Data Services (ADDS) (www. aviationweather.gov) —the Aviation Digital Data Service (ADDS) makes text, digital and graphical forecasts, analyses, and observations of aviation- related weather variables available to the aviation community. The ADDS graphics and charts are often easier to interpret than those of the AWC website. 

• Helicopter Emergency Medical Services (HEMS) Weather Display (www.weather.aero/hems) —the ADDS development team created an experimental tool designed to show weather conditions for short-distance and low-altitude flights common for the helicopter emergency medical services (HEMS) community at the request of the FAA. [Figure 4-28] This interactive site allows the user to determine ceiling and visibility and winds (at 500 foot increments) for an area as small as 5k$^{2}$. While not specifically targeted nor designed for the balloon pilot’s use, the information obtained from this site is helpful to the pilot planning a flight at some distance from a normal weather reporting facility. 

## Interpreting Weather Charts and Reports 

A weather chart is any chart or map that presents data and analysis that describe the state of the atmosphere over an extended region at a given time. Weather charts provide a picture of the overall movement of major weather systems and fronts and are used in flight planning. 

Three useful weather charts for balloon pilots are: surface analysis, weather depiction, and radar summary charts. These three charts present current weather information and provide “big picture” information for weather systems across the United States. The composite moisture stability chart, constant pressure analysis charts, and significant weather prognostic charts provide additional information for flight planning. 

Knowledge of all these weather charts, reports, and forecasts may not be necessary for the pilot planning a local flight, but an understanding of large scale weather patterns and systems bring a greater understanding of how those systems affect local weather. It is important to gain an understanding of the primary charts used, and develop interpolation skills to be able to perform safe, adequate flight planning. 

## Surface Analysis Chart 

The surface analysis chart is computer-generated, covers the contiguous 48 states and adjacent areas, and is transmitted every 3 hours with an analysis of the current surface weather. It shows the areas of high and low pressure, fronts, temperatures, dew points, wind directions and speeds, local weather, and visual obstructions. [Figure 4-29] 

Surface weather observations for reporting points across the United States are also depicted on this chart. Each of these reporting points is illustrated by a station model. 

• Type of observation—a round model indicates an official weather observer made the observation. A square model indicates the observation is from an automated station. Stations located offshore give data from ships, buoys, or offshore platforms. 

• Sky cover—the station model depicts total sky cover and will be shown as clear, scattered, broken, overcast, or obscured/partially obscured. 

• Clouds—cloud types are represented by specific symbols. Low cloud symbols are placed beneath the station model, while middle and high cloud symbols are placed directly above the station model. Typically, only one type of cloud will be depicted with the station model. 

• Sea level pressure—sea level pressure given in three digits to the nearest tenth of a mb. For 1,000 mb or greater, prefix a ten to the three digits. For less than 1,000 mb, prefix a nine to the three digits. 

• Pressure change/tendency—pressure change in tenths of mb over the past 3 hours. This is depicted directly below the sea level pressure. 

• Precipitation—a record of the precipitation that has fallen over the last 6 hours to the nearest hundredth of an inch. 

• Dew point—dew point is given in degrees Fahrenheit. 

• Present weather—over 100 different weather symbols are used to describe the current weather. 

• Temperature—temperature is given in degrees Fahrenheit. 

• Wind—true direction of wind is given by the wind pointer line, indicating the direction from which the wind is coming. A short barb is equal to five knots of wind, a long barb is equal to ten knots of wind, and a pennant is equal to 50 knots. 

