The trends method involves determining the speed and direction ofmovement for fronts, highand low pressure centers,and areas of clouds and precipitation. Using this information,the forecaster can predict where he or sheexpects those features to be at some future time.For example, if a storm system is 1000 miles west of yourlocation and moving to theeast at 250 miles per day, using the trends methodyou would predict it to arrive in your area in 4 days.
Mathematics
(1000 miles / 250 miles per day = 4 days)
Using the trends method to forecast only a few hours into thefuture is known as "Nowcasting" and this method is frequently used to forecastprecipitation. For example, if a line of thunderstormsis located 60 miles to your northwest and moving southeast at 30 miles per hour,you would predict the storms to arrive in your area in 2 hours.Below is an example of using the trends method to forecast the movementof a cold front.Initially, the cold front moved 800 miles during the first 24 hours, from the central Plains to theGreat Lakes.
Using the trends method,you would predict this weather system to move another800 miles in the next 24 hours, reaching the East Coastof the United States.The trends method works well when systems continue to move at thesame speed in the same direction for a long period of time. If they slowdown, speed up, change intensity, or change direction, the trendsforecast will probably not work as well.
 persistence | Terms for usingdata resources.CD-ROM available. |  other methods |
