•  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. •  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. 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.  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 Interpreting Weather Charts and Reports 4-29