The 1958 to 1999 climatology of warm season subweekly 850 hPa meridional geostrophic wind over Texas (hereafter; 850vg) with respect to subweekly Midwestern United States warm season precipitation indicates that monitoring 850vg in near real time can be used to anticipate changes in the submonthly trend of Midwest precipitation. Changes in the trend of precipitation over the central United States have the potential to change the outlooks for central United States crops thus having great economic importance. Because of the strong relationship between low-level southerly flow and central United States precipitation, the precipitation trend usually changes soon after a change in the trend of the low-level flow. A simple dual moving average analysis was performed on the low-level flow variable. For the long term average, a 10-day moving average was selected while a 5-day moving average was selected for the short term. About 80% of the times the meridional wind 10-day running average was at a relative maximum (minimum), the 5-day running average trend break and subsequent crossover indicated the next 7 to 10 days would indeed be relatively dry (wet). To follow trends of low-level flow, which has potential to be useful for considering future growing season precipitation fluctuations and subsequent crop outlook, a web page was assembled.

The main feature of the page (http://www.mesonet.agron.iastate.edu/~windmill/RIpage.html) is the automatic chart generation accomplished with JpGraph 1.6.3 (http://www.aditus.nu/jpgraph/). The charts allow users to follow the latest changes in the trend of the low-level flow and Midwest precipitation. Users can also interactively select summer segments from past years to examine more closely or to compare to the current situation. The 850 hPa heights used in the calculation of the geostrophic meridional wind are automatically downloaded from the University of Wyoming upper air archive (http://weather.uwyo.edu/upperair/sounding.html). Daily precipitation reports are automatically downloaded from National Climatic Data Center (ftp://ftp.ncdc.noaa.gov/pub/data/coop-data/). Moving averages are computed and updated automatically after the data is recorded. Methodology and suggestions for use are provided on the page.