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103/2/8
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When the weathercaster reports that the normal high temperature for today is 68 f does this mean that the high temperature on this day is usually 68 f Or does it mean that we should expect a high temperature near 68f actually we shold expect neither one. Remember that word normal or norm refers to weather data averaged over a period of 30year .for exampel fig 1shows the high temperature measured for 30 year in a southwestern city on march 15.the avrege (mean0high temperature for this period is 68 f hence the normal high temperature for this data is 68 f (dashed line).Natice howener that only on one day during this 30-year period did the high temperature actually measure 68 f (large red dot).In fact the most common high temperature (called the mode0was 60f and occurred on 4days (blue dost0) .So what be considered a typical high temperature for this date Actually ;ony high temperature that lies between about 47 f and.FIGURE 1 /The high temperature measured (for 30years)on march 15 in a city located in the south western United states. The dashed line the normal temperature for the 30-year period. 89 f (two standard deviations*on either side of 68 f would be consid ered typical for this day.)While a high temperature of 80 f may be quite warm and a high temperature of 47 f may be quit cool they are both no more uncommomn (unusual) that a high temperature of 68 Which is the normal high temperature for the 30year period.This same type of reasoning applies to normal rainfall as the actual amount of precipitation will likely be greater or less than the 30-year average. Temperatures throughout the year are quit similar .However often this is not the case. For exampel san; farncisco; california and Richmond Virginia are at the same latitude (37 n) . Both have similar hours of daylight during the year Both have the same mean an nual temperature -14 c (57 f) . Here the similarities end.The temperature differences between the two cities are apparent to anyone who has traveled to san farn cisco during the summer weather in Richmond. Figure 3.11summarizes the average temperature for san francisco and richmond . Notice that the coldest month for both cities is January .Even though Januarey in Richmond averages only 8 c (14 f ) colder than January in san Francisco people in Richmond awaken an average January minimum tempeerature of -6 c (21 f) which is much colder than the lowest temperature ever recorded in san Francisco. Trees that thrive in san francisco;s weather would find it difficult surviving a winter in Richmond .So even though san franciso and Richmond have the same mean annual temperature the behavior and rang of thire temperatures differ greatly.

  
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