Precipitation

Last year in Oneonta Total precipitation: 42.16” Average: 42.22” ( )

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

(309 – 404 inches) (8 – 30 inches)

Topographical map of Hawaii.

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

Same as the previous slide, but only for January. Notice the interesting pattern in New York State.

Same as before, but only for July. The most precipitation falls in the southeast. Why?

Clouds and precipitation form when humid air rises. Here are three of the most common mechanisms for causing air to rise. Orographic upliftConvection Frontal lift, also occurs with cyclones and surface air convergence

You’ve seen this before. Now focus on the green bars: Nov 11, 3.4” Sep 30, 2.34” Jul 10, 1.58” Oct 29, 1.39” The top 4 events produced over 20% of the year’s precipitation What hypotheses can we offer, based on these observations?

Next exercise: Precipitation Climatology 1.Go to WeatherBase: There you will find monthly and annual records for thousands of cities across the world. 2.Find Binghamton, NY (US). Its records start with Average Temperature:

3. Farther down, Binghamton’s record of average monthly precipitation looks like this: 4. Using the Excel spreadsheet provided, Binghamton’s data has been entered. Excel plots a line graph of the monthly values with no smoothing:

5. Next, find and enter the average monthly precipitation for San Diego CA, Seattle WA, Honolulu HI, Tallahassee, FL, and Des Moines, IA. Use the entry with just the city name which is usually the main airport station. Put all data on the same graph with Binghamton. Once you enter the data, the lines will be drawn automatically. 6. Answer the following: a. How does the average monthly precipitation vary through the year at each station? b. What patterns show up in the data for these six stations? c. What factors account for the precipitation values at these stations through the year? 7. Using Weatherbase, find a city in the U.S., other than the ones used here, which has a summer maximum, i.e., the precipitation is greatest in June, July, or August. What factors account for the summer maximum in your city? 8. Using Weatherbase, find a city in the U.S., other than the ones used here, which has a winter maximum where the precipitation is more than three times the summer minimum. What can account for the winter maximum in your city? Submit your answers and spreadsheet electronically to Due on Tuesday

Here’s a closeup of the interesting pattern of precipitation in NY state. What creates this pattern?

Lake Effect is one big reason for upstate precipitation

Fig 7.31 here

Nov 18, 2014 Buffalo

Basically, this is convection

So what causes the precipitation to be higher in the southeastern corner of the state (near NYC)? Participation points for any answers consistent with what we know about precipitation.

Tropical Cyclones can have an immense effect on precipitation totals

The precip is enhanced because of proximity to the ocean (also in extratropical cyclones and fronts)

Precipitation Summary 1.To get precipitation you must have enough water vapor. Proximity to water sources will tend to correlate with higher 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 instability Fronts 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.

What happens in places that don’t get a lot of precipitation? Like these

The desert Southwest

Mojave Desert Death Valley Sierra Nevada Mts (wet)

The Dust Bowl, 1930’s

Average annual upper air (500 mb) pattern

Average January upper air

Average July upper air

It’s normally dry in the southwest but abnormally so in 2014)

Even drier in California in 2016 (but no drought left in Plains )

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? The answer to be found in the General Circulation (next)