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Hot and dry conditions are expected this week across much of the Northern Plains. In fact, 100 F degree temperatures are likely across portions of southern and western South Dakota on Tuesday, June 26th.
Rainfall amounts across the area this spring and early summer have been quite variable, with some areas receiving plentiful rainfall whereas other areas have been abnormally dry. The chart below lists the precipitation amounts from Aberdeen, Watertown, and Pierre for the period May 1 – June 24, 2012. While both Aberdeen and Pierre have seen below normal rainfall in May and June – Watertown has seen above normal rainfall.




Observed Precipitation

May 1 – June 24

Normal Precipitation

May 1 – June 24

Departure from Normal

May 1 – June 24




- 3.90”




- 2.09”






A graphical depiction of precipitation trends over the last 60 days is shown below. Figure 1 is the observed precipitation for the last 60 days.  Precipitation has ranged from about 2 inches in the Aberdeen area, to as much as 10" in western Minnesota.


Figure 1: Current 60-Day Observed Precipitation


Figure 2 the departure from normal precipitation, and Figure 3 the percent of normal precipitation. As noted in the images, the driest areas (yellow and orange shading) appear to be concentrated from the James River Valley eastward to the Sisseton Hills and into west-central Minnesota. Conversely, above normal precipitation (green and blue shading) has occurred in east-central South Dakota, and also just north of Mobridge.


Figure 2: Current 60-Day Departure from Normal Precipitation


Figure 3: Current 60-Day Percent of Normal Precipitation

Not surprisingly, this variability in precipitation is highly correlated to thunderstorm activity. It is not uncommon for one county to be abnormally wet, whereas an adjacent county is abnormally dry.  In extreme situations, this gradient in precipitation will occur within a county - or even just across town!



NWS Experimental Forecast of Reference Evapotranspiration for Short Canopy Vegetation

Evapotranspiration (ET) is a critical piece of crop water use and management in understanding how much water is needed to sustain optimal crop production.  ET is the amount of water loss from soil (evaporation) and plants (transpiration) to the atmosphere, typically measured in inches of water per day.  ET is challenging (and expensive) to measure directly, but it can be estimated with a few relatively simple measurements of air temperature, humidity, wind speed, and solar radiation.   The National Weather Service offices in South Dakota have come together to present ET forecasts on a single webpage:

This page displays the forecast ET amount each day, out to seven days.  There is also a cumulative ET forecast total for the current seven day period.  The National Weather Service updates these forecasts at least twice a day, so they are always current during the growing season.   

For more information on forecasting crop water use, see a corresponding article from iGrow - a service of the South Dakota State University Extension.