A Changing Storm Track at Cedar Creek

The Fall LTER Coordinating Committee meeting was hosted by the Cedar Creek site. We field-tripped between the remarkable armada of experimental plots that were from time to time referred to as Tilmanesk by the locals. We also roamed the now-rare oak savanna that marks the boundary between the northern tall grass prairie and forests to the north an east. In my study of the tracks of the centers of cyclones over the Prairie Peninsula of North America for the Konza Prairie, I took a look at passing storms over Cedar Creek.

The National Weather Service charts the path of each storm center from sequences of daily weather maps. To be called a cyclone there must be at least one closed isobar persisting for at least two consecutive weather maps. They usually last much longer and travel great distances. I have digitized these storm track maps for each month for each year beginning in 1875. My Konza study, reported in the last CED issue, involved a PCA analysis of monthly frequencies of the passage of storms through a set of 2.5 degree lat by 5.0 degees long grid cells.

One of the PCs represented storms that track south and eastward out of the west central Canada along the forest-prairie border and into central Minnesota. Subsequently these storms tend to turn east across the Great Lakes. Some call such storms Alberta Clippers as they are fast moving storms that arise in that province. The loadings on that PC were mapped and are shown in the illustration above. The Arrow indicates the central axis of this storm track and the contours of loadings can be thought of as an index of the dispersion of the storms about the mean track.

Seasonal and annual history of Cedar Creek storm track are remarkable. The changing frequency of storms along this track mark a major climate change for the region. As these storms, to their south, have access to warmer and moister air often of tropical origin, the realized harvest of rainfall can be substantial. Ground water recharge and fire danger may both have been modulated in climatic time and perhaps have played a role in the movement of the forest-prairie ecotone.