AOSC200Lect21

AOSC200Lect21 - AOSC 200 Lesson 21 WEATHER FORECASTING...

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AOSC 200 Lesson 21
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WEATHER FORECASTING FOLKLORE Red sky at night, shepherd’s delight, Red sky in morning, shepherd’s warning When spiders’ webs in air do fly The spell will soon be very dry PERSISTENCE The weather tomorrow will be the same as the weather today (two times out of three) CLIMATOLOGY This takes persistence one step further The average weather say for a particular month is the same each year * ‘COLD in December – HOT in July’ In July the Sun is hot, Is it shining? No it’s not.
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Fig. 13-1, p. 375 “Decision tree” forecast
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Climatology Forecast of a White Christmas
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TREND AND ANALOG We know that persistence forecasts will eventually be wrong because weather does change. A trend forecast assumes that the weather-causing patterns are themselves unchanging in speed, size, intensity, and direction of movement (this is called steady-state). For instance: we know that an approaching cyclone will bring rain (weather does change) but assume that the amount of rain or its speed will not change along the path the cyclone will travel. The analog forecast also acknowledges that weather changes, but unlike the trend method, it assumes that weather patterns can evolve with time. The main assumption is that weather repeats itself . Therefore, this method “searches” for past weather patterns that are similar (analog) to the current situation. In this sense, the future weather patterns “should” be similar to those that happened in the past.
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Trend forecast based on the assumption that a mid-latitude cyclone moves up the East coast unchanged.
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This note was uploaded on 01/30/2012 for the course AOSC 200 taught by Professor Hudson during the Fall '08 term at Maryland.

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AOSC200Lect21 - AOSC 200 Lesson 21 WEATHER FORECASTING...

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