A study of the integrated areas of high positive vorticity (low pressure) predicted by one of the National Weather Service's prognostic models has shown a significant decrease in the accuracy of the forecast product for the time period of approximately two days following a solar sector boundary crossing. In addition, analysis of the observed integrated vorticity areas for the winter months of a three year period provided independent verification of the results obtained earlier by Wilcox et al. (1973) relative to the interplanetary magnetic field and Roberts and Olson (1973a) relative to measured geomagnetic activity. Taken as a whole, the present results suggest that short wave structures develop or exhibit growth as they are guided into the auroral or subauroral zone by global scale pressure patterns.