UP TO 10 DAYS 



Figure 4. Estimated initial data requirements to forecast for a point at the 500-miUibar sur- 

 face (about 6 kilometers) at latitude 45°N. For a forecast period of up to 30 hours, initial 

 data are required from a strip at the same altitude over the Northern Hemisphere; 30 hours- 

 2 days, a thin layer of atmosphere over part of the Northern Hemisphere; 2-4 days, a deep 

 layer of atmosphere over most of Northern Hemisphere; 4-5 days, a deep layer of atmos- 

 phere over the entire Northern and part of the Southern Hemisphere plus sea-surface data; 

 5-10 days, same part of atmosphere as for 4-5 days plus the ocean to 4 meters; and 10 days- 

 2 months, atmosphere over entire globe plus the ocean to 100 meters. (Adapted from Hallgren, 

 R. E., "World Weather Program, " TRW Space Log, spring-summer 1968) 



11-12 



