Aviation Weather Services

Effective September 1, 2015, the four-panel Low Level of a precipitation area, but the specific character of that area SFC-240 chart was replaced with a two-panel chart. The new (snow, rain, hail, VIRGA, etc.) cannot be determined. For two-panel chart will be the same as the top two panels in the this reason, ATC refers to all weather areas displayed on ATC former four-panel chart, depicting the freezing level and areas radar scopes as “precipitation.” of IFR, MVFR, and moderate or greater turbulence. The bottom two panels of the chart have been removed. In lieu of these ARTCC facilities normally use a Weather and Radar bottom two panels, an enhanced surface chart that includes Processor (WARP) to display a mosaic of data obtained fronts, pressure, precipitation type, precipitation intensity, and from multiple NEXRAD sites. There is a time delay between weather type, is displayed. The green precipitation polygons actual conditions and those displayed to the controller. will be replaced by shaded precipitation areas using the The precipitation data on the ARTCC controller’s display National Digital Forecast Database (NDFD) weather grid. could be up to 6 minutes old. The WARP processor is only used in ARTCC facilities. All ATC facilities using radar Figure 13-13 depicts the new two-panel significant weather weather processors with the ability to determine precipitation prognostic chart, as well as the symbols typically used to intensity, describe the intensity to pilots as: depict precipitation. The two panels depict freezing levels, • Light turbulence, and low cloud ceilings and/or restrictions to • Moderate visibility (shown as contoured areas of MVFR and IFR conditions). These charts enable the pilot to pictorially • Heavy evaluate existing and potential weather hazards they may • Extreme encounter. Pilots can balance weather phenomena with their aircraft capability and skill set resulting in aeronautical When the WARP is not available, a second system, the decision-making appropriate to the flight. Prognostic charts narrowband Air Route Surveillance Radar (ARSR) can are an excellent source of information for preflight planning; display two distinct levels of precipitation intensity that however, this chart should be viewed in light of current is described to pilots as “MODERATE and “HEAVY TO conditions and specific local area forecasts. EXTREME.” The 36- and 48-hour significant weather prognostic chart is ATC facilities that cannot display the intensity levels of an extension of the 12- and 24-hour forecast. This chart is precipitation due to equipment limitations describe the issued twice a day. It typically contains forecast positions and location of the precipitation area by geographic position or characteristics of pressure patterns, fronts, and precipitation. position relative to the aircraft. Since the intensity level is not An example of a 36- and 48-hour surface prognostic chart is available, the controller states “INTENSITY UNKNOWN.” shown in Figure 13-14. ATC radar is not able to detect turbulence. Generally, ATC Radar Weather Displays turbulence can be expected to occur as the rate of rainfall or Although ATC systems cannot always detect the presence intensity of precipitation increases. Turbulence associated or absence of clouds, they can often determine the intensity with greater rates of precipitation is normally more severe than Figure 13-13. Significant weather prognostic chart. 13-16