After five days in the thin, dry air of Colorado, I have returned to the hot, muggy summer of the American Midwest. Though the intense sunshine of the Front Range often produces afternoon highs in the 90s, the high elevation and thin atmosphere promote rapid cooling at night and early morning lows drop into the 50s. By contrast, the thick blanket of humid air in the Midwest serves to minimize the radiation of heat and we awaken to temperatures near 70.
By mid July, the jet stream has moved into Canada and high pressure builds across the Southern Plains. Pacific storms and their associated cold fronts are diverted across the northern tier of States and precipitation in most of the Central and Eastern U.S. is limited to scattered, pop-up thunderstorms and the occasional tropical system. At the same time, this high pressure over the plains is partly responsible for the seasonal monsoon of the Southwest, pulling Gulf moisture across Mexico and into the Four Corners region.
The sultry conditions will persist until the jet stream drifts southward, allowing pockets of cool, Canadian air to invade the Heartland. Though storms across the northern States may send weak cold fronts into the Midwest, significant, lasting relief must await a buckling of the jet stream itself. Don't count on that until mid September or so!
