Chase Log: July 06th, 2003

Click on any of the SPC products below (Convective Outlooks, Watches, or MCDs) to see the SPC's "Severe Thunderstorm Events" page pertaining to this event.

MAP

Total Distance: 480 miles
Target Area: Marshall, MN
Chase Area: Benson to Alexandria to Sauk Centre, MN
Maximum SPC Risk category: Moderate
Watches: Tornado Watches 656, 660, 661, and 662
Mesoscale Discussions (MCDs): 1644, 1651, 1652, 16556, 1658, 1661, 1665, and 166

A good chance for catching some tornadic storms today as good shear and high instability juxtposed in western Minnesota. An approaching cold front was to enter western Minnesota by mid-late afternoon and spark off scattered convection in moist warm sector. The cap today was expected play little role in inhibition. Wrong.

I headed out the door solo around noon, aiming for anywhere west of New Ulm. When I checked the surface map down there, I noticed a significant problem -- the dewpoints were actually dropping. It seems that an MCV spawned from the following night's convection in IA was causing strong subsidence in the lower-middle levels of the atmosphere and actually lowering the dewpoints. I did notice that the RUC model early in the morning was dropping dewpoints, but that model was showing upper 40 tds for western Minnesota, which was just ridiculous, so I discarded the run totally. Oops.

I sat southwestern Minnesota until early evening, meandering slowly westward in hopes that the cap, originally not expected to be too much of a problem, would break in this less-moist-than-forecast environment. I decided to head north on the notion that the cap would be weaker the farther north I went, but I was slightly hesitant to move anywhere because the Td in Ortonville was 59! By the time I was through Marshall, I noticed strong thunderstorms blossoming well north northwest of me. One of these storms was quite visually-impressive, showing a nice backsheared anvil (not that impressive, however, seeing how upper-level winds were generally ~40kts) and good overshooting top. I was nearing Benson, MN, when I got word of a tornado warning fora storm a few miles north of Morris. I jetted northward out of Benson, at which time a nice, rather large wallcloud came into my view. At one point in time, it appeared that two wallclouds were in my view: one from the t-warned storm north of Morris, and another trying to develop from a cell just to its southwest. As I neared I-94 and Alexandria, these two cells began to conglomerate into more of a linear-type system, as was evidenced by the lifting of the wallcloud and the development of a shelf cloud. Since I had to work at 10pm (althought I told them I'd be late), and being able to see that this thing had little chance of producing a tornado, I decided to give up and head home.

All in all, a rather disappointing chase. This was just another example in all too many of how overnight convection can ruin the following day's chase; if it's not a remnant surface cold pool, it's other mesoscale features (e.g. the MCV and related subsidence) that are not handled well by models.