Hurricane Florence passed very near Bermuda on 11 Sep (IR image | water vapor image), with a peak wind gust of 111 mph reported on the island. The radius of high winds associated with Florence was rather large, and the tight pressure gradient between the tropical cyclone and a large area of high pressure over southeastern Canada (above) was creating strong winds that prompted the issuance of high surf and other marine warnings/advisories along much of the US east coast. GOES-12 low-level visible winds (below) indicated the extent of the strong winds along the western periphery of Florence, with several targets having speeds of 34 knots or greater (bold green or cyan wind barbs on this closer view) a considerable distance from the storm center.

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Severe convection developed in eastern portions of the Texas panhandle region, which produced wind gusts to 67 mph and golf-ball size hail (1.75 inch diameter) around 20:20 to 20:30 UTC (3:20 to 3:30 PM local time) in parts of Cottle county, TX (the county outlined on the images above); a few hours later, this convection was also responsible for flash flooding in that particular county. The 16-panel image (above) shows visible and IR channel images from all 4 of the current operating GOES satellites (GOES-10, GOES-11, GOES-12, and GOES-13) at 20:30 UTC; the development of that same storm can also be viewed at 1-minute intervals from GOES-10 (below), which is still in Super Rapid Scan Operations (SRSO) as the satellite is being re-positioned to 60 W longitude. During the hours leading up to convective initiation, a curved outflow boundary from earlier thunderstorms was apparent across that region, and AWIPS GOES sounder-derived lifted index and total precipitable water depicted an axis of instability (LI = -10.4 C) and moisture (PW = 51 mm / 2.00 in) that was extending west-northwestward into Cottle county along that outflow boundary.

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Cold air was streaming southwestward across Lake Superior, behind a strong Canadian cold front (temperatures the following morning dropped to 19 F at Embarrass MN and 28 F at Hayward WI). On the MODIS true color image (below, left), the appearance of the cloud bands that formed over the lake closely resembled “lake-effect snow bands” that often form in the winter (due to the large temperature difference between the relatively warm water surface and the cold arctic air). While the air behind this particular front wasn’t cold enough for lake-effect snow, there were some areas of lake-effect rain and drizzle in the UP of Michigan and in northern Wisconsin. Once we get into the winter months, MODIS products such as the Cloud Phase and the Cloud Top Temperature (below, right) will be helpful for determining whether snow or freezing rain/drizzle will be the likely precipitation type over a given region. In this case, the MODIS Cloud Phase product indicated thatwater phase clouds (blue enhancement) covered most of Lake Superior (MODIS IR and Cloud Top Temperature values were several degrees below freezing, so it was likely supercooled water droplets these clouds); farther to the south, over northern Wisconsin and the UP, a band of more intense rain showers and thunderstorms (with some cloud to ground lightning strikes) was depicted as ice phase clouds (pink enhancement), with corresponding IR and cloud top temperature values colder than -30 C (dark blue enhancement on the MODIS CTT and IR images).

Note to AWIPS users: Jordan Gerth made a modification to the MODIS Cloud Phase product, to allow AWIPS cursor display of the actual phase category (along with a phase label in the color bar).

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GOES-10 Super Rapid Scan Operations (SRSO) visible and 10.7 micrometer InfraRed (IR) imagery at 1-minute intervals shows a nice view of a small thunderstorm that developed off the Texas coast this morning. The pulsing of overshooting tops could be seen in the visible imagery, along with periods of colder cloud top temperatures (around -65 C, darker red enhancement) in the IR imagery. Toward the end of the animation, an outflow boundary can be seen moving westward away from the convection. Since the storm was offshore, there were no reports of any hail or severe weather with this particular convection…but it was interesting to watch in the 1-minute imagery. Real-time GOES-10 SRSO visible imagery can be viewed here or here.

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