October « 2007 « CIMSS Satellite Blog

Wildfires in southern California

October 21st, 2007

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.

Posted in Air quality, Fire detection, GOES-11, MODIS | No Comments »

TROWAL in the upper Midwest, October 2007

October 16th, 2007

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.

Posted in General interpretation, GOES-12 | No Comments »

Atlantic Tropical Depression 15

October 11th, 2007

The National Hurricane Center began issuing advisories on Tropical Depression 15 (located in the central Atlantic, east of Bermuda) on 11 October 2007. A GOES-12 visible image with ASCAT wind data sourced from the CIMSS Tropical Cyclones website (above) suggested that maximum winds were only around 30 knots.

There was strong southwesterly flow aloft over the developing cyclone with increasing deep layer wind shear, so the bulk of the deep convection was confined to the northeastern quadrant of TD #15 — an animation of GOES-12 visible images (below) shows that the low-level center was close to becoming exposed in that strong wind shear environment.