Chase Logs 2007
The Midnight Express: Shelf Cloud Rolls over the N. Twin Cities
July 13, 2007
10:30pm-11:30pm
Anoka, MN
About a week ago I installed a version of Windows XP Pro. on my home workstation (now the third operating system to co-exist on the system) designed solely for operating weather programs, primarily WeatherScope, IDV, and StormWarn. With these programs I can now turn my desktop into a weather monitoring monster, capable of tracking different aspects of a storm at the same time. Since I completed the system just prior to my vacation, today (Sunday) would be the first day I could try it out. And sure enough, a line of showers and thunderstorms, some borderline severe, developed over eastern North Dakota and cruised southeastward at 30mph. At 6:00pm, with the storms located near Fergus Falls, I booted into my new OS and launched WeatherScope and StormWarn. Within minutes I was actively monitoring and archiving all radar levels and satellite images of the storm system.Cell P0 became severe shortly before 10:00pm, and at 9:58pm the NWS MPX issued a severe thunderstorm warning for SE Morrison, Mille Lacs, and Benton Counties. I noted an area of rotation appear on the MPX composite velocity scan, as well as the base reflectivity scan (a small hook echo that lasted just a few sweeps) at 10:10pm as the system crossed the Morrison/Mille Lacs/Benton County border. This rotation increased in strength, becoming TVS as it passed through Isanti County between 10:30 and 11:00pm. The storm became more linear after 11:00pm, but the rotation persisted near the front of the cell. The five radar images below depict the fluctuating line of thunderstorms as they move towards the Cities. The first composite radar scan shows the line of storms as storm D0 achieved severe status (over SE Morrison County with the 3D wind shear icon). The next two images, a composite velocity and base reflectivity slice, show the area of rotation over the Morrison/Mille Lacs/Benton County border. The final two scans highlight the TVS rotation over Isanti County and the storm becoming linear over Anoka County at 11:10pm.
Originally I did not plan on chasing this storm, but with the lightning coverage increasing through the trees on the north side of my yard, I decided to make a dash for the Anoka High School parking lot, again, to watch the storm pass by. After weathering a shower courtesy of a cell that developed directly over me, I started taking photos and monitoring the main event. A gust front spanned the skyline from due north to about 70 degrees from north (ENE). The cell was moving at a good clip, so I didn't have time to set up the DSLR but was able to get the PowerShot A630 P&S camera ready and firing. The storm's gust front is highlighted by both lightning flashes and the lights of the Twin Cities in the five photos below. Note the rain curtain evident just behind the front. Since the storm was moving so fast and I used a 15 second shutter speed, the storm will appear slightly blurry. The first four photos were enhanced to better illuminate the storm's structure, so I decided to include the original photos, which located below the first row.
Gusts of cold wind whistled eerily through my camera tripod as the front loomed overhead. The distance between me and the lightning, resulting in only heat lightning for me, made the scene even more haunting. While peering into the main rain filled storm cluster, now located about 15 miles to the ENE, I noticed a pencil thin funnel shape extending about a third of the way from the base of the storm. By the time I swung the camera around and adjusted the aperture/film speed, however, the cloud had disintegrated into a heap of scud. But over the course of the next few minutes, the scud reorganized around that particular region of the storm and formed what appeared to be a small wall cloud. But it was night and the intermediate flashes of lightning that offered me a brief glimpse of the cloud could easily play tricks on my eyes. I settled for the idea that it was just scud that might be organizing around the TVS area. The first four photos below trace the history of the cloud, and are once again enhanced to show the cloud in greater detail. The original photos from this batch are below the enhanced ones. The last photo is an overview of the storm as it moved into Ramsey County and is not enhanced. Note the very low scud cloud over the bulldozer on the left side of the photo.
It was now 11:30pm, and with the storm already located in northern Ramsey County and weakening fast, I called it a night. Back to updating the website. . .
