An occluding cyclone (at 1 minute intervals)
A deepening mid-latitude cyclone (located over southeastern Colorado / southwestern Kansas at 12 UTC) began to transition from the mature stage to the occluded stage during the morning hours on 21 September. The tell-tale occluding cyclone signature (consisting of a wrapping “dry slot swirl”) was depicted on the 8-km resolution GOES-10 6.7 micrometer “water vapor channel” imagery (above) — a 200-image QuickTime animation shows the evolution of the occlusion process at 1-minute intervals, since the GOES-10 satellite was still in Super Rapid Scan Operations (SRSO) mode. By 15 UTC, HPC analyzed the feature as an occluded low; later that afternoon several tornadoes were reported in northcentral Kansas as the low moved over that region.
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Additional structure is revealed on the 1-km resolution MODIS water vapor imagery at 17 UTC. Also, strong winds were causing a plume of blowing dust along the advancing cold frontal boundary — this dust plume exhibits a signal (yellow to orange enhancement) on the MODIS 11-12 micrometer IR difference product (below). Note the observation of blowing dust at Lubbock, Texas (station identifier LBB in the lower left corner of the image), where westerly surface winds were 38 mph (gusting to 47 mph); the blowing dust was reducing visibility to 3 miles at that particular time.
