National Drought Mitigation Center

Average Precipitation and Drought Severity

How do you determine your farm or ranch’s susceptibility to drought?

You’ll start by developing a good understanding of historical precipitation in your area. Historical drought information for a particular region can be used to determine overall risk to drought as well as frequency and severity of drought for individual locations.

By monitoring conditions in your area, you can have an idea of how current precipitation and temperature values compare to long-term averages over various time frames.

What's My Average Precipitation and When Does it Usually Occur?

Find average precipitation, when precipitation typically occurs, and average temperatures in your area -

View sample graphs here.

According to a study by Smart et al. (Historical Weather Patterns: a Guide for Drought Planning. Rangelands. 2005), the amount of spring precipitation during April, May, and June is a good indicator of the current year’s forage production on ranches in the northern mixed-grass prairie of the Great Plains. Since more than 90% of the total annual forage is produced by July 1, rainfall received after this time will not greatly benefit grass production. Therefore, understanding the historical occurrence of drought during April-June can be very important for ranch planning in the northern Great Plains.

What's the Precipitation Range for My Area?

Discover the lowest precipitation by month on record for your area at Are there steps you could take to be prepared for receiving that level of precipitation again?

This information is valuable for designing your ranch operation to withstand such departures from the average. What changes would you have to make in your activities to survive a 50% reduction in annual precipitation? What about a 25% departure from average over a period of five years or longer?

How Often Does Drought Occur in My Area and How Long Does it Last?

NCDC Climate Data Online

Historical information based on climate divisions is useful in determining drought conditions over a broad area over time.

The user can find historical temperature and precipitation data, as well as drought severity indices, by region, state, or smaller geographic units. Data is presented in numerical charts or graphs. The graph shown here is of the Palmer Drought Severity Index, with the yellow regions indicating drought.

PDSI of Nebraska Panhandle region 1980-2009

Use the "Retrieve Data by Division" tab, select your state and division, click on "static graph" and precipitation, and select any time period. You'll get a line graph showing precipitation by year, average precipitation over the time period, and a running average of precipitation. The one year moving average of precipitation will show you a good trend for when your historical droughts have occurred. Notice that you can also choose to just have a certain, critical month's precipitation displayed. So you can see how often you've had a drought going into your dominant grass growing months. To identify your climate division, see the NOAA Climate Division Map or the NWS Climate Division Map.