Rope Cloud in the Gulf of Mexico

October 23rd, 2007 |

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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.

Wildfires in southern California – Part 2

October 22nd, 2007 |

GOES-11 visible images (Animated GIF)

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.

MODIS true color image

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MODIS 3.7 µm IR image

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).

GOES-11 3.9 µm IR image

Wildfires in southern California

October 21st, 2007 |

GOES-11 3.9 µm IR images (Animated GIF)

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.

IDEA MODIS AOD

TROWAL in the upper Midwest, October 2007

October 16th, 2007 |

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An occluded storm that affected the upper midwest early in the morning of 16 October displayed cloud characteristics that can be interpreted as the development of a TROWAL (A TROugh of Warm air ALoft). The highest, coldest clouds tops that at the start of the loop are in north-central Illinois can be interpreted as the edge of the warm conveyor belt in this occluded system. As that edge translates northeastward across Lake Michigan and into lower Michigan, cold cloud tops blossom over southeast and east-central Wisconsin and then move westward or northwestward. These cold clouds can be interpreted as the development of precipitation in the TROWAL airstream, which originates in the warm sector and then turns cyclonically into the cold air on the cyclonic shear side of the warm conveyor belt.

TROWALs are characterized by warm air aloft, and RUC model output for this day shows warmth aloft in a region that overlays a region of precipitation. Here is the temperature on the 320 K theta-e surface at 0900 UTC — the midpoint of the IR loop above. A tongue of warm air — which would be a depression on this isentropic surface — extends west-northwestward from eastern Wisconsin towards northwest Wisconsin. Note how well the canyon correlates spatially with radar echoes shown here. Note also that the warm tongue at 850 mb, shown here, does not overlay as well with the radar echoes. (A loop of the three images is here). TROWALs move through isobaric surfaces and lie along isentropic surfaces. Care must therefore be taken when interpreting thermodynamic parameters associated with a TROWAL.