Chase Logs 2009
Boats or Storms?: Shelf Cloud Spectacle over the Harbor
July 22, 2009
12:00pm-8:00pm
Duluth, MNAs the summer of boredom (weather-wise) rolls on, it only figures that my first really good storm encounter of the year would happen when I didn't want it to. In fact, I got to deal with TWO storms today! Boy, I sound pathetic, but with the way this severe weather season has been going, I'll take anything. Anyway, today's event occurred during my wee-long vacation in Duluth, where all I do is watch boats. So one can imagine that I was none too pleased when CU/CB towers began cluttering the lakeshore shortly before noon. I snapped a few photos of the clouds (first row of photos below), but otherwise continued watching boats. One storm to the northwest of the city boasted a nice anvil (first three photos of second row below). As I left the canal after the arrival of a boat, I noticed a collapsing anvil on the northern Wisconsin shore which featured virga tentacles hanging from it has the updraft dissipated and the ice crystals in the anvil fell back toward Earth (last two photos in second row below).
The northern storm arrived shortly after 1:00pm, and besides featuring a nice gust front (first three photos below), produced little more than some rain showers and a some miscellaneous rumbles of thunder. However, it still prevented me from watching a boat enter the harbor. As the northern half of the storm moved out over the lake, it quickly interacted with the stable marine air and dissipated by 3:00pm. The southern half over northern Wisconsin retained its intensity (last two photos below of the weakening northern half and strong southern half).
The most exciting part of the day occurred when I watched the radar screen during the mid-afternoon hours as the outflow boundary from the dying storm system propagated northwestward over the southern Arrowhead of Minnesota. Meanwhile, another outflow boundary from a line of storms in west central St. Louis County raced southeastward, on a crash course with the other outflow boundary. They collided just before 3:30pm about 50 miles north of Duluth, and by 3:45pm a line of strong thunderstorms had erupted along this convergence zone. The radar images below from 12:57pm to 4:39pm document this event. The blue arrows denote the initial outflow boundary from the storm over Duluth at the time, the black arrows denote the northern outflow boundary, red arrows indicate a secondary outflow boundary that emerged from the southern half of the Duluth storm, and the dark blue arrows indicate the outflow boundary from the line of storms spawned by the initial collision.
The photos below from 4:10pm to 5:10pm, showcase the event from the deck of my hotel room, looking northwest.
Shortly after 5:15pm, the shelf/gust front began creeping over the hillside, and soon was draped like a curtain across the entire skyline. And lo and behold, another boat arrived. So I did double duty for awhile, watching the encroaching shelf to my northwest and photographing the vessel entering the ship canal. At times, shark's teeth reached down from under the shelf and looked ominous for a few minutes before dissipating. As the shelf spread across the harbor, it soon became easier to take photos of the boat and the storm, since they were now in the same frame :) (last photo below).
It quickly became apparent, however, that the storm was fading. The shelf cloud quickly dissipated as it moved overhead and left a mess of scud clouds in its wake. It rained for a good hour as the system moved overhead, but little else came from this storm.
The three radar images below from 5:11pm to 7:39pm confirm the quick death of the storm as its energy source faded and the lake airmass took over. The dark blue arrows denote the outflow boundary of the system.
