SURFACE WIND AND CLOUD AMOUNT FORECAST. The four panels of this chart are valid 12, 18, 24, and 30 hours from the data base time. On this computer-plotted chart, station circles represent the major cities. Circles are open, one-quarter darkened, three-quarters darkened, or totally darkened, representing clear, scattered, broken, or overcast (total) cloud cover. A number appears below each station circle, representing the forecast flight-weather category (1 for IFR, 2 for MVFR, and 3 for VFR conditions). The forecast surface winds are plotted as standard wind barbs on each station circle.

PROBABILITY OF PRECIPITATION AND PRECIPITATION TYPE FORECAST. This chart has four panels that are valid 12, 24, 36, and 48 hours from the data base time. Each has isolines showing probability of precipitation from 05 percent to 95 percent. Symbols representing precipitation type are plotted over the major U.S. cities where the precipitation probability is equal to or greater than 25 percent. These symbols are : for rain, * for snow, and for freezing rain.

The mid-range surface forecast is produced once a day from the 1200Z data collection. This chart, shown in figure 4-3-17 has four panels. The first panel is valid at 1200Z of day 3 following the data collection. The second panel has the surface forecast for 1200Z on day 4. The next panel has a 500-millibar forecast for 1200Z on day 4, and the last panel has a surface forecast for 1200Z on day 5. Each surface forecast has isobars showing the pressure centers, and frontal positions. Using knowledge of the general weather to expect with different frontal systems and a stations climatology, a forecaster should have no problem making a 3-to 5-day outlook using this product. General wind directions and speeds may be forecast using the isobar orientation and spacing as a guide.

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