Drove up to Ebbetts Pass on SR4 late afternoon Friday. Skies were hazy blue over the Central Valley except for a thin dirty brown smoke band over the east foothills. Air over the Sierra looked hazy blue. At dawn had an unblocked view to the west and saw a more dense brown band had moved in above the Sierra foothills. At sunrise although Ebbetts Pass and areas north were hazy blue, areas just south in the Sonora Pass area and to the east over Monarch Pass looked hazy smoky. By 8am the smoky air to the south surprized me by moving north and I could smell smoke that was disgustingly unpleasant. I was working closeup wildflowers photography and not landscapes, so that had no impact on my reason for being there.
I had been in the area 4 weeks before when wildflowers were at peak which was surprising good despite the dry conditions and it appeared it would stay that way for at least a week or two longer. However the droughty conditions made quick work of green vegetation making for considerably less flowers than would be expected a couple to three weeks past peak. Grassy meadow areas are already quite dry and brown except in more permanent seep and streamside areas. After rambling about a few hours, at mid morning I decided to bail so drove home. Skies were smoky hazy until I reached Bear Valley, after which they were increasingly blue all the rest of the way home. Even the brown band over the Sierra foothills was gone.
The smoke situation was somewhat a mystery though I can speculate. One issue was why was there a band of smoke over the Sierra foothills that apparently thickened overnight? The jet stream and upper atmosphere for days has consistently been blowing west to east or southwest to northeast. Thus that flow would not have caused that smoke band as the Aspen Fire is well to the south-southeast. Lower down in the hot Central Valley, a thermal low often sets up rotating CCW. At night in stagnant air conditions in the lower and mid atmospheric levels like we have been having, the smoky air up the San Joaquin drainage sumps down canyon back towards the valley. So am guessing, plumes of sumping smoke got caught up in a thermal air circulation blowing north. Then in the morning as the valley air heats up and expands, that pushes east up canyons. Additionally smoky air at mid levels above west slopes bank up against Sierra crest areas and also may have rotated north and been helped by the upper air also moving west to east. Much of that hazy smoky air probably does not show up on the satellite until it becomes dense so I've learned another useful lesson. The current pattern is supposed to hold till the following weekend when the low off the Oregon coast is finally supposed to move east followed by more normal August weather though long range forecasts are rather speculative. Given the droughty conditions I may not have any reason to return to the Sierra till leaf season at the end of September.