AEROGRAPHER'S MATE 3 & 2 



209.304 



Figure 11-11.— Isallobars. 



Weather Analysis 



A thorough study of the weather on the sur- 

 face chart has been made as the map has been 

 analyzed. It is now time to indicate the inten- 

 sity and characteristics of the precipitation and 

 of some of the other weather phenomena. This 

 is done by shading and/or use of symbols as 

 shown in table 11-1. 



Movement Analysis 



The next step is to determine the present 

 rate of motion of the fronts and pressure sys- 

 tems. The past rate of motion is already indi- 

 cated from the past history of the pressure 

 systems and the fronts. After the past and pre- 

 sent motions of fronts and pressure systems are 

 determined, their future movement is considered. 



It is standard procedure in weather offices 

 to place the expected movement of pressure 

 systems and fronts on the current weather 

 chart. (See fig. 11-12.) 



Two of the primary methods for determining 

 movement of these systems are by their move- 

 ment on previous charts and by the pressure 



tendencies on the current chart. For example, 

 the low in figure 11-12 the position for each 

 12-hour period is noted and placed on the chart. 

 If the 1200Z chart for the ninth day of the month 

 is being analyzed and a low-pressure system 

 is located at position 3, and on the previous 

 12-hour charts it was located at positions 1 and 

 2, it could be assumed that 12 hours hence 

 the system would be at position 4. 



High-pressure areas move toward areas of 

 positive pressure tendencies; low-pressure areas 

 move toward areas of negative pressure tenden- 

 cies. 



Summary 



The following summary is the recommended 

 procedure for analyzing a surface weather map: 



1. Draw the fronts and pressure systems of 

 the preceding map on the current chart with a 

 yellow pencil. Study the previous charts for 

 historical sequence. 



2. Sketch the isobars lightly, preferably one 

 pressure system at a time. Isobars should be 

 adjusted (fig. 11-8) in order to locate the fronts 

 as accurately as possible. 



3. Locate and sketch the fronts. 



4. Redraw each isobar smoothly and neatly. 

 Label all isobars. 



5. Draw the fronts in appropriate color. 



6. Label the high-pressure areas with an H, 

 using a blue pencil. Label the low-pressure 

 areas with an L in red pencil. 



7. Draw the isallobars in appropriate color 

 and label tham. 



8. Label air masses. 



9. Color the precipitation areas. 



10. Determine the past, present, and future 

 rate of motion of fronts and pressure systems. 



International Analysis Code 

 (FM 45.( ) and 46.( )) 



Underway at sea, you may find that be- 

 cause of other duties time cannot be spared 



208 



