The large (74,000-acre) “Day Wildfire” was still burning in the Los Padre National Forest just northwest of Los Angeles on 17 September — the MODIS true-color image (above) shows the thick plumes of smoke drifting westward. Strong offshore winds helped the fire (which had been burning since 04 September) to grow quickly and spread to the west on this particular day. A QuickTime animation of GOES-11 visible images the following day (18 September) shows that the smoke began drifting in a more northwesterly to northerly direction as the surface winds gradually shifted direction.

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The AWIPS MODIS 6.7 micrometer “water vapor channel” image (above) depicts an excellent example of a mountain wave signature over parts of the southern and central Rocky Mountains region, as strong winds associated with a jet stream axis were interacting with the rugged terrain. Note that the corresponding MODIS visible image reveals that very few clouds were present across much of the area where the mountain waves were evident (southern Colorado and northern New Mexico). Aircraft occasionally experience moderate to severe turbulence when they encounter mountain waves — in this case, there were numerous pilot reports of turbulence (below), which included this report in the Denver area at 19,000 feet:

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DEN UUA /OV DVV 224064/TM 1931/FL190/TP E120/TB CONT MOD OCNL SEV/RM SEV MTN WV-15 SECONDS-PILOT SAID LIKE HITTING A WALL-ZDV

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On the Terra MODIS true color image (above) an extensive cumulus field can be seen forming over the land surfaces surrounding Lake Michigan on 15 September — daytime heating along with the evaporation of abundant soil moisture (from significant precipitation on 12 September and 13 September) allowed the cumulus clouds to form quickly as the day progressed (Aqua MODIS image 3 hours later). In lower Michigan, a differential heating boundary is quite evident, where the dissipation of thick morning fog and stratus was delaying the cumulus formation; a well-defined lake breeze boundary also developed along the Lake Michigan lakeshore counties, which was quite apparent in Wisconsin and Illinois on the later Aqua MODIS image.

Two other items of interest on the MODIS true color image above: (1) the first regional sign of peak Autumn tree color is showing up in southern Ontario; note the amber color along the eastern shore of Lake Superior (closer view), and (2) farther east, the light gray features over Quebec are areas of smoke aloft, from wildfires in Ontario 1-2 days earlier.

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GOES-11 visible imagery (above) revealed a nice example of a von Karman vortex street downwind of Guadalupe Island (located off the west coast of Baja California: MODIS true color image). Guadalupe Island has a maximum elevation of about 1.3 km, which was high enough to act as a barrier to the northwesterly boundary layer wind flow; the resulting vortex pattern is apparent in the marine stratoculumus field. A QuickTime animation shows the evolution of the individual vortex features — note that some vortex circulations are cyclonic, while others are anticyclonic.

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