A cold front pushed through the Midwest yesterday but, except for some clouds and a wind shift, was barely noticeable in central Missouri. While most cold fronts arrive with blustery conditions, accompanied by rain, thunderstorms or snow, yesterday's mellow transition was due to several factors.
The center of the storm was up in Minnesota and its low pressure zone was broad; in addition, it was not energized by the jet stream and was drifting slowly to the east. Its trailing cold front was likewise sluggish and separated two air masses that differed little in temperature and humidity. As a result, the passing front was only marked by a band of clouds, a few scattered showers and a gentle north breeze.
The more typical cold front, attached to an energized, "tightly wound" center of low pressure, arrives with a bang, as disparate air masses collide and cold, dry air undercuts warm, humid air ahead of the front. Significant pressure differences across this moving barrier generate strong, southwesterly winds ahead of the front and brisk, northwesterly winds behind it. Finally, the "lift" provided by the potent storm triggers rain, snow, hail, or thunderstorms as the warm, humid and unstable air is forced to rise.
Though yesterday's event lacked the drama of a typical cold front, it was the leading edge of a large, cool air mass which will bring more seasonal conditions to our region. By the end of the week, highs will be in the 60s and lows will approach 40. October has returned!
