Thunderstorms are rumbling across Missouri this morning, the leading edge of a cold front that will bring us the first significant chill of the season; the rest of the week is expected to be dry, with highs in the 60s (F) and lows in the 40s. Spring and fall are the battle-grounds of winter and summer and this appears to be winter's first jab.
The weather gyrations of spring and fall coincide with an undulating jet stream, which creates an alternating pattern of cool and warm weather across the Heartland. Troughs (dips in the jet) allow Canadian air to spill southward while ridges (northward curves in the jet) open the Midwest to a warm, humid flow from the Gulf of Mexico. As autumn progresses, the jet will gradually move southward and flatten out; broad troughs will dominate the region and the chill of winter will become entrenched. By then, winter will have won the battle and summer will not renew its challenge until March.
