The Dome of August

After a rather cool and pleasant July, we are back in the heat of a Midwestern summer. As is typical in August, a broad dome of high pressure has developed over the Southern Plains and South-Central States. Within this ridge, sinking air, clear skies and light winds can produce stifling heat, often combined with high humidity.

Expanding and contracting over the next month, the dome will deflect Pacific Fronts to the north, keeping the Northern Plains and Upper Midwest in a stormy pattern while augmenting the prolonged Texas drought. This late summer ridge is also partly responsible for the annual, Southwest monsoon; combined with heat-induced low pressure over the deserts of southeastern California and southern Arizona, a fetch of moisture (from both the Gulf of California and the Gulf of Mexico) is pumped across Mexico and into the Four Corners region. Riding the outer edge of the dome, this moisture-laden air flows northward across the mountains of New Mexico and Colorado, feeding storms along the Front Range and, eventually, the Northern Plains.

Trapped under the ridge of high pressure, our landscape begins to dry out. The greenery fades, wetlands retreat and streams slow to a trickle. Until the jet stream moves southward with the waning sunlight or unless a tropical system moves in from the Gulf, the dog days of August will prevail.