Chapter 11 — WATCH ROUTINES (CONTINUED) 



Table 11-1. — Standard precipitation coloring 

 Precipitation areas Coloring 



Areas of continuous Light green shading, 

 precipitation. 



Areas of intermittent Light green hatching, 

 precipitation. 



Areas of showers. 



Areas of drizzle. 



Areas of past 

 thunderstorms. 



Areas of present 

 thunderstorms. 



Areas of fog. 



Green shower symbols. 



Green drizzle symbols 



Red thunderstorm 

 symbols. 



Green thunderstorm 

 symbols. 



Light yellow shading. 



®' 



»® 



209.308 

 Figure 11-12. — Forecast movement of fronts and 

 pressure systems. 



to plot all ship and coast station reports avail- 

 able for drawing a weather map. On such oc- 

 casions, an analyzed weather map and/or 

 prognosis showing the centers of pressure sys- 

 tems, the fronts, and isobars drawn from data 

 given in the coded analysis message may meet 

 the local requirements. Also, in cases of com- 

 munications failure which precludes the receipt 



of facsimile transmissions, this coded analysis 

 or prognosis may be the only source upon which 

 the weather officer has to base his forecasts. 



This code reduces to a numerical code form 

 a weather map prepared at forecasting centers 

 of meteorological servicer. Data included in 

 these messages give the types, characteristics, 

 central pressures, locations, and movements of 

 pressure systems and position points for use in 

 drawing the fronts and isobars. Types of fronts 

 (whether warm, cold, occluded, or stationary) 

 and the values for the isobars are also indi- 

 cated in the messages. The message may be 

 either a current map analysis with indications 

 as to movement or development, or a prognostic 

 map analysis. 



The international code, FM 46( ), was de- 

 signed primarily for marine use. It is an abridged 

 form of FM 45( ), and the symbolic letters 

 and figures h&ve the same meaning in both 

 codes. 



The symbolic form and an explanation of 

 the letter specifications of these codes, refer 

 to the International Meteorological Codes (YEAR) 

 and Worldwide Synoptic Broadcasts NA50-1P-11. 

 For an example of a plotted map of the Inter- 

 national Analysis Code, see figure 11-13. 



UPPER AIR CHARTS 



Map analysis includes not only surface weather 

 charts but also upper air charts. The upper 

 air charts used in conjunction with the surface 

 charts are essential for accurate forecasting. 

 With the aid of upper air charts, the fore- 

 caster gets a 3-dimensional view of the synoptic 

 situation. 



The flow pattern of the air in the free at- 

 mosphere above the layer of frictional influ- 

 ence next to the earth is indicative of the type 

 of weather that will occur at the surface of the 

 earth. The direction in which pressure sys- 

 tems, fronts, tropical storms, and the like 

 move depends upon the windflow above the fric- 

 tional layer of the atmosphere. It is necessary 

 to determine this factor from upper air charts. 



The basic upper air charts in use today 

 are termed CONSTANT PRESSURE CHARTS, 



209 



