Precipitation

From your text

From your text

This is how your text shows the average precipitation over most of the planet.

Another look, this one in color.

From your text, clouds and precipitation form when humid air rises.

Here are three of the most common mechanisms for causing air to rise.

Orographic uplift Convection

Frontal and cyclonic lift

Hawaii has some of the highest annual average precipitation records.

What are the factors which combine to produce the immense rainfall maximum seen here?

Topographical map of Hawaii.

http://rainfall.geography.hawaii.edu/rainfall.html

Excluding Hawaii and Alaska, this is the U.S. average annual precipitation (rain + melted snow/ice)

http://www.prism.oregonstate.edu/normals/

Same as the previous slide, but only for January.

Notice the interesting pattern around the Great Lakes.

http://www.prism.oregonstate.edu/normals

Same as before, but only for July.

The most precipitation falls in the southeast. Why?

http://www.prism.oregonstate.edu/normals

Last year in Oneonta

Total precipitation: 48.68”Average: 42.04” (1970-2000)

July 224.69”

What creates this pattern of precipitation in NY?

December-January-February average snowfall (inches)

Tropical Cyclones can have an immense effect on precipitation totals

So, the pattern of precipitation in NY can be explained.

Where you see rainfall (and where it is dry) is NOT random

Precipitation Summary

1. To get precipitation you must have enough water vapor. Proximity to water sources will be common to places with high average precipitation.

2. Upward vertical motion is the second requirement. Places with high average precipitation also have strong mechanisms providing lift.

Lift mechanisms:Topographic relief (mountains)Convection or instabilityFronts or cyclones (both tropical and extratropical)

Wet and dry areas on the globe form patterns, suggesting a systematic organization of these elements. This is due to the General Circulation patterns.

So, what happens in places that don’t get a lot of precipitation?

It’s normally dry in the southwest but abnormally so this year)

“Normal” pattern (surface and upper air)

Drought pattern (1988)

Some places are drier than others. Those that regularly experience upper air ridges will be dry, even during non-drought years.

Where does that occur on average around the world and WHY?

Next: General Circulation