In the March 5th release of the U.S. Seasonal Drought Outlook, drought conditions are forecast to develop over parts of the Tri State area by May 2009. The forecast is the result of much below normal precipitation over the winter months and persistent La Nina conditions in the Pacific Ocean. The map below shows the percent normal of precipitation which fell between December 2008 and February 2009. Areas in red received less than half of normal, and those areas are the most likely to develop drought in the coming months. This includes places like Russell Springs, Gove and Hill City in northwest Kansas, a small portion of extreme southwest Nebraska including McCook, and parts of northeast Colorado south of the Interstate. Areas in orange are also below normal in recent precipitation, but the risk of drought in those areas is less. Finally, the areas in green and purple have seen above normal precipitation, such as Yuma and Kit Carson counties in Colorado, and drought is not likely to develop there.
The other factor for possible drought development is La Nina conditions in the Pacific Ocean. La Nina is below normal sea surface temperatures near the equator. La Nina conditions have persisted since last summer, and are forecast to continue through at least this summer. The charts below show the percentage of years with above normal precipitation (green), near normal precipitation (yellow) and below normal precipitation (brown) during La Nina events. Each chart represents a 3-month period, centered over northwest Kansas. The number of below normal years, or possible drought conditions, increases during the early spring months, peaking in April-May-June (AMJ, first chart, second row). In fact, during La Nina events, over 50% of the April-May-June periods have experienced below normal precipitation. There have also been years of near normal and even above normal, but below normal is more prevalent. So, given the current La Nina pattern, it seems a safe bet to say that below normal precipitation is likely (but not certain) during the next few months, which will compound the already dry conditions which have developed over the winter season and lead to possible drought development.
JDK March 11, 2009.