Clouds tumbled over Carson's skies Wednesday, the anvils building ominously in the afternoon heat. By late afternoon, they unleashed havoc on in the form of wind, rain, lightning, and fires.
The National Forest Service estimates 40 forest fires have been sparked by lightning since Friday along the eastern slope of the Sierra between Bridgeport and Doyle. Thunderstorms have also been strong in the Sierra: Truckee received .37 inches of rain Monday.
The monsoonal pattern is generated when moisture moves north from the deserts of the southwest. Originating in the Gulf of California, moisture is pushed north by a ridge of high pressure over the four corners area. If the pattern is right and there is low pressure in the Los Angeles area, moisture is directed into Nevada.
This monsoonal moisture is not an uncommon occurrence, but this year it arrived early. Tucson reported the earliest monsoonal moisture flow ever, and Phoenix the second earliest.
"Usually we don't see a consistent monsoonal pattern until late July or August," Otteson said, noting that according to one theory, sea surface temperatures in the Gulf of California could be the culprit. Warmer sea surface temperatures there increase the amount of moisture available in the southwestern deserts. That additional moisture was further augmented by the remnants of hurricane Carlotta off of Mexico.
Temperatures have averaged 5.5 degrees higher for the month of June, but Otteson isn't ready to attribute these disturbances to global warming.
Otteson doesn't know if trend will continue, but we could see and end to the storms if the high pressure ridge over the four corners area dissipates, and the low pressure from the Gulf of Alaska pushes monsoonal moisture to the south and east.