Topical Outline

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Topical Outline Types of Precipitation Measurement
of Precipitation Causes of Precipitation
(Appendix D-5) Representing Average Precipitation
Over an Area On Tuesday Characterizing
Probability of Extreme Precipitation Events
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Types of Precipitation Rain Snow Hail
Sleet Freezing rain Drizzle Mist Occult
Precipitation
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Rain gage with Alter type wind shield
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Rain catch deficiency ()
From Dingman, Physical Hydrology.
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Weighing lysimeters in central Ohio measured
approximately 3.5 inches per year more
precipitation than standard rain gages.
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Measuring throughfall in a forest canopy
Where occult precipitation is sometimes discovere
d
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Doppler Radar Tower
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Cause of Precipitation
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Orographic Effect
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Intense rain in a narrow band near the front
More uniform, less intense, distributed over a
larger area.
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Convective storms tend to cover a small area
and can be intense.
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Heat Island Effect
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Estimation of precipitation over an area from
point Measurements
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Arithmetic Average in in P 1 S pi
S pi/n n i1 i1 P average
precipitation n number of rain gages pi
individual gage measurements Area Weighted
Average in in P 1 S pi ai S pi ai/A
A i1 i1 A total watershed area ai
area of watershed receiving precipitation
pi ai/A fraction of watershed area receiving
precipitation pi
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Different approaches to fitting a surface to
point measurements
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Orographic Effect
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Hypsometric method where elevation influences
precipitation
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