Cynthia and Craig’s warnings have two high probability hail swaths for the lead supercell and the trailing storm that continued to advect downstream and decrease slightly in probabilities until they updated the threat areas. At one point the NWS issued one SVR polygon to cover both the storms but then broke it up. Upon review, it’s apparent the advecting threat area allows for more continuous aging off of the swath on the back sides than the NWS severe wx statements. They kept updating everytime the storm moved out of the threat area. There is still some difficulty of comparing hail-only swaths with NWS polygons which cover hail and wind.

There some difficulties handling multi-vertex polygons, such as moving them. Cynthia struggled with moving the polygons. Sometimes she’d inadvertently create multiple vertices.

Brian and Bill were grappling with rapid cycling process of the lead supercell. Their probabilities were more marginal than that of the hail. There was no confirmation despite the number of chasers out there. But they kept the probabilities as high as they were given the mesocylone strengths and the potential for hidden tornadoes. Each meso quickly became wrapped in precip. Later on a line developed south of KDDC with intense horizontal shear across the gust front.

Several vortices wrapped up along the interface and as a response a long, low probability (20%) tornado threat area was added.

The NWS did not issue any tornado warning for the supercell.

There’s some discussion about what TOR probability constitutes a standard warning? Craig would go 40% and Bill would go 50%. Both Bill and Craig don’t relate their warning decision making to a number though Bill didn’t have a problem associating a warning threshold probability here.

Software ran well, even with the big TOR threat area that Brian put out on the squall line.

Jim LaDue (EWP Weekly Coordinator, 5-9 May)