A 200-image animation (29 MB QuickTime movie, above) of Super Rapid Scan Operations (SRSO) GOES-10 visible channel imagery shows the development of supercell thunderstorms at 1-minute intervals across northern Arkansas and southern Missouri between 17:00 and 22:07 UTC (12:00 Noon and 5:07 PM local time) on 22 September. During that time period, this particular convection produced softball-size hail (4.25 inches in diameter) and multiple tornadoes across southern Missouri (including one producing F4 damage near Crosstown), and 3.0 inch diameter hail in northern Arkansas (SPC storm reports). Heavy rainfall and flash flooding was also reported, with 10.16 inches of rain falling at Myrtle, Missouri (near the Missouri/Arkansas border). Additional details on these storms are available from the St. Louis MO and Springfield MO NWS offices.
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An AWIPS MODIS/GOES comparison of the InfraRed (IR) and visible channel images around 19:30 UTC (below) shows well-defined enhanced-v signatures on the IR “window channel” imagery. At that time, the IR cloud top temperatures in the vicinity of the overshooting tops over northern Arkansas were as cold as -86 C on the 1-km resolution MODIS IR data, versus -68 C on the 4-km resolution GOES IR data. A 100-image QuickTime animation of the GOES-10 IR window channel imagery shows the evolution of the various enhanced-v signatures during the 17:45-20:19 UTC time period (12:45-3:19 PM local time).

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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.

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Cold air advection in the wake of a secondary cold front helped to generate some well-defined lake effect rain bands over Lake Huron on 20 September (QuickTime animation of GOES-12 visible images). The cold air mass allowed daily minimum temperatures at the surface to fall into the 30s to 40s F across the Great Lakes region (getting as cold as 26 F at Hayward WI and Embarrass MN). The air temperatures aloft (850 hPa, near 5000 feet) were 0 to -3 C; as this cold air flowed over the relatively warm waters of Lake Huron (water temperatures of 15-18 C), the release of the thermal instability helped elongated cloud bands to form (generally parallel to the boundary layer wind direction. The AWIPS MODIS cloud phase product indicated that most of the lake-effect clouds were water phase clouds (blue enhancement), although it did flag portions of the longest cloud band as “mixed phase” (darker gray enhancement) where the cloud top temperatures were as cold as -12 C. With daytime surface air temperatures warming into the 50s F, the precipitation falling from these cloud bands was in the liquid form; similar cloud band features produce significant lake-effect snowfall during the colder winter months.

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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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