Vortex2 tornado study finally gets some twisters to study

A proven way to reduce the incidence of dangerous weather phenomena is to schedule a multi-million dollar field experiment to study the phenomena. Up until this past weekend, that has certainly been true of this year's $10 million Vortex2 tornado study. The 7-week study (which also runs next year) has deployed an armada of over 100 storm chasing vehicles across the Great Plains this Spring, but has largely been frustrated by an exceptionally quiet tornado season. Tornado activity in May was less than half of what was observed last year in May, thanks to a ridge of high pressure that has dominated the weather. The residents of Tornado Alley ran out of luck over the weekend, though, as a strong low pressure system and associated cold front brought severe weather and multiple tornadoes to the region. Sixteen tornado reports were received by NOAA's Storm Prediction Center yesterday, and three on Friday. The team of University of Michigan students that has been writing our featured Vortex2 blog caught some excellent pictures of tornadoes on both Friday and Sunday. Yesterday was probably the last best chance for the Vortex2 project to document a strong tornado, since the project ends this Saturday and no significant tornado outbreaks appear likely for the remainder of this week.

Aurora, Colorado tornado yesterday
A tornado with a 3/4 mile wide debris cloud swept through Aurora, Colorado yesterday, staying on the ground for 8 - 11 miles and damaging a shopping mall, but causing no deaths or injuries. The tornado passed close to one of the high-resolution Terminal Doppler Weather Radars (TDWRs) that we now feature on our web site (see the radar FAQ for more details on these great new additions to our radar offerings). Posted below are the reflectivity and Doppler velocity images from the tornado, showing the amazing fine-scale details these high-resolution radars offer.



Figure 1. Radar reflectivity (top) and Doppler velocity (bottom) from the Denver, Colorado Terminal Doppler Weather Radar (TDWR), which caught the classic signature of a supercell thunderstorm tornado over Aurora, Colorado. A tornado dropped down from the low-level mesocyclone inside the parent supercell thunderstorm at the time of these images. Yellow colors located right next to greens/blues indicate that winds are moving towards and away from the radar in close proximity, the signature of strong rotation at low levels. Also visible on the plot are the winds spreading out from a downdraft on the rear side of the tornado. Black arrows denote the direction of wind flow. The dryline was bent back into a E-W orientation near Denver, creating an area of moisture convergence, which triggered thunderstorm formation.

Western Caribbean disturbance unlikely to develop this week
As area of disturbed weather over the Western Caribbean has brought rains of 2 - 3 inches over portions of Nicaragua and Honduras over the past few days. Wind shear is a high 20 - 30 knots over the disturbance, and no computer models are indicating that the disturbance will develop this week.

Jeff Masters, with help from wunderground's tornado expert, Dr. Rob Carver