Jesse Risley
Staff member
I chased with Eugene Thieszen. We left Breckenridge, CO early Thursday morning for the initial target of Broadus, MT. Storms were expected to go up along a pre-frontal trough ahead of the cold front, beneath a seasonably strong H5 flow. The only factor that I initially had concerns about was low-level storm relative helicity, though models indicated that it was going to increase closer to 0z. Seeing moisture flow that peaked into very high percentile ranges for late June had me concerned that this could be a significant event given the magnitude of the instability that far north being depicted by the models, and that was supported by actual 12z rawinsonde data with very favorable surface moisture pulling into NE and MT.
CAMs were depicting several different supercells developing across eastern Montana and remaining discreet, at least for the first few hours. Based on surface analysis reviewed at Douglas, Wyoming during a lunch stop, we felt southeast Montana would be the more optimal play. As we headed up towards Broadus, we watched the agitated Cu field begin to form northwest of Gillette by mid-afternoon. After a quick fuel stop, the storm that would go on to produce the tornado spectacle was born southwest of Broadus. We took Highway 212 southeast and began following the storm. It struggled initially, especially the first few hours, with weak and disorganized low-level rotation and occasional shear funnels. The storm began to take on a much more impressive structure north of Alazeda, when It produced its first tornado, which was fairly hard to see because of the contrast. As we followed it east, as it got closer to the state line, it began producing a series of tornadoes, and the supercell would go on to produce no less than 7 tornadoes as it tracked into South Dakota well after dark. I didn't even have very good contrast on all of them. SRH values began to spike, concomitant with the 850 mb jet speed increase, and low-level southeasterly flow ramped up across the area right around 7 p.m. local time (these storms formed well south of the warm front). I am still a little bit in shock that it put on the tornado show that it did, but this type of moisture return into these easterly upslope areas of the high plains tend to reward handily as long as storms move into "CAPE bomb environments" with uncapped air in an otherwise favorable warm sector with easterly / southeasterly low-level flow.
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CAMs were depicting several different supercells developing across eastern Montana and remaining discreet, at least for the first few hours. Based on surface analysis reviewed at Douglas, Wyoming during a lunch stop, we felt southeast Montana would be the more optimal play. As we headed up towards Broadus, we watched the agitated Cu field begin to form northwest of Gillette by mid-afternoon. After a quick fuel stop, the storm that would go on to produce the tornado spectacle was born southwest of Broadus. We took Highway 212 southeast and began following the storm. It struggled initially, especially the first few hours, with weak and disorganized low-level rotation and occasional shear funnels. The storm began to take on a much more impressive structure north of Alazeda, when It produced its first tornado, which was fairly hard to see because of the contrast. As we followed it east, as it got closer to the state line, it began producing a series of tornadoes, and the supercell would go on to produce no less than 7 tornadoes as it tracked into South Dakota well after dark. I didn't even have very good contrast on all of them. SRH values began to spike, concomitant with the 850 mb jet speed increase, and low-level southeasterly flow ramped up across the area right around 7 p.m. local time (these storms formed well south of the warm front). I am still a little bit in shock that it put on the tornado show that it did, but this type of moisture return into these easterly upslope areas of the high plains tend to reward handily as long as storms move into "CAPE bomb environments" with uncapped air in an otherwise favorable warm sector with easterly / southeasterly low-level flow.
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Cute Little Twister
