The large wildfires continued to burn across parts of southern California on 23 October 2007. AWIPS images of the GOES-11 imager visible channel (upper left panel), 6.7 µm water vapor channel (upper right panel), 10.7 µm IR channel (lower left panel), and the GOES-11 Sounder 4.0 µm IR channel (lower right panel) reveal an interesting signature of the smoke pall that had been transported westward out over the Pacific Ocean — on the water vapor channel! Since H2O is a byproduct of combustion, the water vapor content of the aged smoke pall is somewhat elevated compared to the rather dry ambient atmosphere over the eastern Pacific Ocean; this allows a subtle signature of the smoke feature to appear on the GOES imager water vapor channel. There is no signal on either of the IR channel images (bottom 2 panels) since smoke is transparent to thermal radiation at those wavelengths.

A comparison of two 500-meter resolution Terra MODIS red/green/blue (RGB) image composites (above) shows a closer view at the fires in the Los Angeles and San Diego region. The MODIS Channel 01/04/03 RGB image approximates the “true color” images that appear on the SSEC MODIS Direct Broadcast site. The MODIS Channel 07/02/01 RGB image takes advantage of the temperature sensitivity of the “near-IR” Channel 07 (2.1 µm) to make the hottest active fires appear with a pink to red enhancement (the red pixels over water are due to sun glint). The large dark burn scar resulting from the 70,000-acre fire just southwest of San Diego (station identifier KSAN) is just starting to become evident on the 07/02/01 RGB image, even through the thick smoke plume seen on the 04/03/01 RGB image.

The IDEA MODIS aerosol optical depth (AOD) trajectory forecast (above) suggested that some of the thick smoke could get recirculated back over portions of northern California within the 48-hour forecast period; however, the trajectory trend indicated that these aerosols might remain just above the boundary layer, which would limit their impact on surface air quality in the San Francisco region. The National Weather Service also provides a 1-hour average vertical smoke integration product as part of their Air Quality Forecast Guidance.

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Rope clouds are elongated lines of cumuliform clouds that develop at the leading edge of an advancing cold front. They are most commonly seen over the ocean, where friction and topography effects that might disrupt the development of a line are minimal. For the example seen today, a RUC temperature analysis over the Gulf to the east of the line show temperatures in the 80s (Fahrenheit) at 1500 UTC; RUC analysis temperatures drop quickly into the 60s and 70s behind the line, even over the warm waters of the Gulf.

Satellites other than geostationary viewed this line. Click here to view the rope cloud as seen by NOAA-17, and click here for the MODIS imagery. Both polar orbiters give higher spatial resolution views — at the cost of lower temporal resolution.

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According to the National Interagency Fire Center, there were 11 fires with a total of 90,679 acres burning in California on 22 October 2007  –  many of the larger fires where described as “0% contained”, and large-scale evacuations were declared from San Diego to Malibu. An animation of GOES-11 visible channel images (above) shows large wildfire smoke plumes being advected a significant distance (up to 1000 miles) westward over the Pacific Ocean. It is interesting to point out that some of the smoke had recirculated back to the coast of California, with additional local eddy circulations evident near the Point Conception region and farther north. Also note the appearance of several plumes of blowing dust/sand farther to the south in Mexico, streaming off of Baja California and also into the northern Gulf of California.

A MODIS true color image (below; 3.8 MB file size) from around 21:00 UTC (2:00 PM local time) helps to differentiate between the smoke plumes (gray shades) and the blowing dust/sand plumes (brown to orange shades). Separate close-up MODIS images are also available centered over Los Angeles and San Diego.

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AWIPS images (from the previous nighttime hours – around 05:30 UTC or 11:30 PM local time) of the 1-km resolution MODIS 3.7 µm IR channel (above) and the 4-km resolution GOES-11 3.9 µm IR channel (below) show a number of very large fire “hot spots” (black to yellow to red enhancement).

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Hot and dry Santa Ana conditions across southern California (with wind gusts as high as 91 mph in Los Angeles county and 87 mph in Ventura county) caused widespread blowing dust/sand (reducing surface visibility to 3 miles at Ontario, station identifier KONT) and created an environment that allowed several large wildfires to burn out of control on 21 October 2007. Note that the dew point temperature at Ontario dropped from 50ºF (+10º C) down to +2ºF (-17º C) in a 3-hour period once the strong northeasterly Santa Ana winds developed. AWIPS images of the GOES-11 3.9 µm IR channel (above) showed very hot pixels (black to yellow to red enhancement) associated with the larger fires (including one fire that caused multiple injuries and at least one fatality near San Deigo, and another fire farther to the north near Malibu – just northwest of Los Angeles KLAX – which shut down portions of the Pacific Coast Highway).

The IDEA MODIS Aerosol Optical Depth product (below) and GOES-11 visible imagery (QuickTime animation) revealed several large plumes of smoke (which could have also contained some blowing dust and/or blowing sand) drifting westward over the adjacent offshore waters of the Pacific Ocean. The airborne particulate matter was causing air quality problems at several sites across southern California on that day.

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