Satellite view of South Texas along the Gulf Coast on Christmas day, 2004. The white area covering Corpus Christi and Brownsville is snow. The probability of measurable snow on the ground in either of these two cities on Christmas day is less than one percent. Yet, Corpus Christi received over 4 inches of snow and Brownsville about 1.5 inches, making it the first snowfall in Brownsville in 109 years. Just days later, the temperature climbed into the 80s (°F). NASA/GSFC Fig. 9-CO, p. 234

Figure 1: Flags indicating advisories and warnings in maritime areas. Figure 1, p. 237

Figure 9.1: The AWIPS computer work station provides various weather maps and overlays on different screens. Fig. 9-1, p. 238

Figure 9.2: Doppler radar data from Melbourne, Florida, on March 25, 1992, during the time of a severe hailstorm that caused $60 million in damages in the Orlando area. In the table near the top of the display, the hail algorithm determined that there was 100 percent probability that the storm was producing hail and severe hail. The algorithm also estimated the maximum size of the hailstones to be greater than 3 inches. A forecaster can project the movement of the storm and adequately warn those areas in the immediate path of severe weather. Fig. 9-2, p. 238

Figure 9.3: Meteogram illustrating predicted weather elements at Buffalo, New York, from 1 P.M. January 18, 1999, to 7 P.M. January 20, 1999. Notice that at 7 A.M. on January 19, the weather is projected to be: sea-level pressure 1007 mb; cloud height 2000 ft.; southwest winds at 15 knots; visibility 10 miles; light snow; air temperature 33°F; dew point 24°F; and the minimum temperature for the day should be 30°F. The forecast is derived from the model output statistics (MOS) of the Nested Grid Model (NGM). Fig. 9-3, p. 239

Figure 9.4: A sounding of air temperature, dew point, and winds at Pittsburgh, PA, on January 14, 1999. Looking at this sounding, a forecaster would see that saturated air extends up to about 820 mb. The forecaster would also observe that below-freezing temperatures only exist in a shallow layer near the surface and that the freezing rain presently falling over the Pittsburgh area would continue or possibly change to rain, as cold easterly surface winds are swinging around to warmer southwesterly winds aloft. Fig. 9-4, p. 239

Figure 9.5: The geostationary satellite moves through space at the same rate that the earth rotates, so it remains above a fixed spot on the equator and monitors one area constantly. Fig. 9-5, p. 240

Figure 9.6: Polar-orbiting satellites scan from north to south, and on each successive orbit the satellite scans an area farther to the west. Fig. 9-6, p. 241

Figure 9. 7: Generally, the lower the cloud, the warmer its top Figure 9.7: Generally, the lower the cloud, the warmer its top. Warm objects emit more infrared energy than do cold objects. Thus, an infrared satellite picture can distinguish warm, low (gray) clouds from cold, high (white) clouds. Fig. 9-7, p. 241

Infrared satellite image Low clouds appear gray High clouds appear white Satellite Infrared energy Figure 9.7: Generally, the lower the cloud, the warmer its top. Warm objects emit more infrared energy than do cold objects. Thus, an infrared satellite picture can distinguish warm, low (gray) clouds from cold, high (white) clouds. Infrared energy Cold High cloud Warm Low cloud Editable Text Fig. 9-7, p. 241

Figure 9.8 Fig. 9-8, p. 242

Figure 9.9a: A visible image of the eastern Pacific Ocean taken at just about the same time on the same day as the image in Fig. 9.9b. Notice that the clouds in the visible image appear white. Superimposed on the image is the cold, warm, and occluded fronts. Watch this Active Figure on ThomsonNow website at www.thomsonedu.com/login. Fig. 9-9a, p. 242

Figure 9.9: Infrared satellite image of the eastern Pacific Ocean taken at just about the same time on the same day as the image in Fig. 9.9a. Notice that the low clouds in the infrared image appear in various shades of gray. Watch this Active Figure on ThomsonNow website at www.thomsonedu.com/login. Fig. 9-9b, p. 242

Figure 9.10: An enhanced infrared image of the eastern Pacific Ocean taken on the same day as the images shown in Figs. 9.9a and 9.9b. Fig. 9-10, p. 243

Figure 9. 11: Infrared water vapor image Figure 9.11: Infrared water vapor image. The darker areas represent dry air aloft; the brighter the gray, the more moist the air in the middle or upper troposphere. Bright white areas represent dense cirrus clouds or the tops of thunderstorms. The area in color represents the coldest cloud tops. The swirl of moisture off the West Coast represents a well-developed mid-latitude cyclonic storm. Fig. 9-11, p. 243

Figure 9. 12: Two 500-mb progs for 7 P. M Figure 9.12: Two 500-mb progs for 7 P.M. EST, July 12, 2006 — 48 hours into the future. Prog (a) is the WRF/NAM model, with a resolution (grid spacing) of 12 km, whereas prog (b) is the GFS model with a resolution of 60 km. Solid lines of each map are height contours, where 570 equals 5700 meters. Notice how the two progs (models) agree on the atmosphere’s large scale circulation. The main difference between the progs is in the way the models handle the low off the west coast of North America. Model (a) predicts that the low will dig deeper along the coast, while model (b) predicts a more elongated west-to-east (zonal) low. Fig. 9-12a, p. 245

Figure 9. 12: Two 500-mb progs for 7 P. M Figure 9.12: Two 500-mb progs for 7 P.M. EST, July 12, 2006 — 48 hours into the future. Prog (a) is the WRF/NAM model, with a resolution (grid spacing) of 12 km, whereas prog (b) is the GFS model with a resolution of 60 km. Solid lines of each map are height contours, where 570 equals 5700 meters. Notice how the two progs (models) agree on the atmosphere’s large scale circulation. The main difference between the progs is in the way the models handle the low off the west coast of North America. Model (a) predicts that the low will dig deeper along the coast, while model (b) predicts a more elongated west-to-east (zonal) low. Fig. 9-12b, p. 245

Figure 9.13: The 500-mb analysis for 7 P.M. EST, July 12, 2006. Fig. 9-13, p. 245

Figure 9.14: Ensemble 500-mb forecast chart for July 21, 2005 (48 hours into the future). The chart is constructed by running the model 15 different times, each time beginning with a slightly different initial condition. The blue lines represent the 5790-meter contour line; the red lines, the 5940-meter contour line; and the green line, the 500-mb 25-year average, called climatology. Fig. 9-14, p. 247

Figure 2: On your home television, the weather forecaster Tom Loffman appears to be pointing to weather information directly behind him. Figure 2, p. 248

Figure 3: In the studio, however, he is actually standing in front of a blank board. Figure 3, p. 248

Table 9-1, p. 249

Figure 9.15: Probability of a “White Christmas”—one inch or more of snow on the ground—based on a 30-year average. The probabilities do not include all of the mountainous areas in the western United States. Fig. 9-15, p. 250

Figure 9.16: Winter weather type showing upper-airflow (heavy arrow), surface position of Pacific high, and general weather conditions that should prevail. Fig. 9-16, p. 250

Figure 9.17: The 90-day outlook for (a) precipitation and (b) temperature for February, March, and April, 1999. For precipitation (a), the darker the green color the greater the probability of precipitation being above normal, whereas the deeper the red color the greater the probability of precipitation being below normal. For temperature (b), the darker the orange/red colors the greater the probability of temperatures being above normal, whereas the darker the blue color, the greater the probability of temperatures being below normal. (National Weather Service/NOAA) Fig. 9-17, p. 251

Figure 9.18: A halo around the sun (or moon) means that rain is on the way. A weather forecast made by simply observing the sky. Fig. 9-18, p. 253

Table 9-2, p. 254

Figure 9. 19: Surface weather map for 6:00 A. M. Tuesday Figure 9.19: Surface weather map for 6:00 A.M. Tuesday. Dashed lines indicate positions of weather features six hours ago. Areas shaded green are receiving rain, while areas shaded white are receiving snow, and those shaded pink, freezing rain or sleet. Fig. 9-19, p. 255

Figure 9. 20: A 500-mb chart for 6:00 A. M. Tuesday, showing wind flow Figure 9.20: A 500-mb chart for 6:00 A.M. Tuesday, showing wind flow. The light orange L represents the position of the surface low. The winds aloft tend to steer surface pressure systems along and, therefore, indicate that the surface low should move northeastward at about half the speed of the winds at this level, or 25 knots. Solid lines are contours in meters above sea level. Fig. 9-20, p. 256

Figure 9.21: Projected 12- and 24-hour movement of fronts, pressure systems, and precipitation from 6:00 A.M. Tuesday until 6:00 A.M. Wednesday. (The dashed lines represent frontal positions 6 hours ago.) Fig. 9-21, p. 256

Figure 9.21: Projected 12- and 24-hour movement of fronts, pressure systems, and precipitation from 6:00 A.M. Tuesday until 6:00 A.M. Wednesday. (The dashed lines represent frontal positions 6 hours ago.) Stepped Art Fig. 9-21, p. 256

Figure 9.22: Surface weather map for 6:00 A.M. Wednesday. Fig. 9-22, p. 259