[Illustration: FIG. 40. Comparison of flight trends and surface weather conditions on April 22-23, 1948. The meteorological data were taken from the U. S. Weather Bureau Daily Weather Map for 12:30 A. M. (CST) on April 23. The nightly station densities and the average hourly station density (shown in parentheses) are as follows: 5. Louisville: 9,100 (1,100) 6. Murray: 16,300 (2,700) 8. Stillwater: 1,900 (500) 9. Knoxville: 15,200 (1,700) 13. Oak Grove: 13,600 (1,700) 16. College Station: 13,300 (1,900) 17. Baton Rouge: 6,200 (1,000) 19. Lafayette: 2,800 (600) 21. Winter Park: 6,200 (700) 23. Tampico: 11,100 (3,700)] [Illustration: FIG. 41. Winds aloft at 10:00 P. M. on April 22 (CST). Winds at 2,000 feet above mean sea level are shown in black; those at 4,000 feet, in white. Velocities are indicated by standard Beaufort Scale of Wind Force. The numbers in circles refer to the stations shown in Figure 40.] Correction: Figures 41 and 45 were inadvertently transposed. [Illustration: FIG. 42. Comparison of flight trends and surface weather conditions on April 23-24, 1948. The meteorological data were taken from the U. S. Weather Bureau Daily Weather Map for 12:30 A. M. (CST) on April 24. The nightly station densities and the average hourly station density (shown in parentheses) are as follows: 1. Albion: 1,100 (300) 2. Ottumwa: 5,500 (900) 4. Lawrence: 5,400 (1,400) 5. Louisville: 13,300 (2,700) 6. Murray: 9,800 (1,400) 8. Stillwater: 800 (100) 9. Knoxville: 8,000 (900) 10. Memphis: 7,900 (1,000) 14. Mansfield: 4,900 (1,200) 16. College Station: 700 (100) 17. Baton Rouge: 1,700 (400) 18. Pensacola: migration negligible 20. New Orleans: 1,600 (800) 21. Winter Park: 2,700 (300) 23. Tampico: 63,600 (6,300) 24. Progreso: 31,300 (3,900)] [Illustration: FIG. 43. Winds aloft at 10:00 P. M. on April 23 (CST). Winds at 2,000 feet above mean sea level are shown in black; those at 4,000 feet, in white. Velocities are indicated by standard Beaufort Scale of Wind Force. The numbers in circles refer to the stations shown in Figure 42.] [Illustration: FIG. 44. Comparison of flight trends and surface weather conditions on April 24-25, 1948. The meteorological data were taken from the U. S. Weather Bureau Daily Weather Map for 12:30 A. M. (CST) on April 25. The nightly station densities and the average hourly station density (shown in parentheses) are as follows: