June 6, 2011 western SD storms

Tour 5 began in Oklahoma City on June 5, with drivers Jon (Woody) Watson, Jennifer Dunn and Brian Morganti.  We made it up to eastern Colorado around Eads and Brandon for some high-based junky cells around sunset, and arrived at our motel in Fort Morgan late.

The chase forecast for June 6 was not clear-cut, as the timing of an approaching disturbance into MT was poor.  A slight risk area was painted from the Rockies in MT eastward through the Dakotas to WI and MI.  Tornado chances were slightly better in MT than in SD.  Here is my forecast post late morning:

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Initially I was thinking that Lame Deer, MT, would be a good starting point for today’s chase. We are expediting northward from Fort Morgan this morning and should be near Broadus by 23Z or so. The negative-tilt trough that is swinging NE-ward towards WY is a tad late (for my liking) with regard to aiding with the lift above the nice E-W CAPE axis from Billings to Broadus to Buffalo SD. But, daylight persists until 10 p.m. or so up there, and we’ll give it a go. I’m not really sure yet as to where to set up along the warm front/CAPE axis. One obvious spot is near Billings, close to the surface low. The road network around there is a little better than most areas of southeastern MT. Moisture might be quite a bit more plentiful near the ND/SD/MT triple-point near Ekalaka, and the 15Z RUC has some nice moisture convergence and a small precip signal there. Otherwise, the latest models are quite stingy with any precip at all through 02-03Z—-UGH.

We’ll continue to Belle Fourche (or Gillette) and figure it out as we go, as usual.

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and, two NOW posts around 6 p.m. and 7 p.m.:

We came up to Belle Fourche. Surface obs suggest a circulation of some sorts, or at least good convergence, just to the west of here in extreme SE MT. A small cell near Devils Tower has our interest and is moving this way, into a good environment in terms of wind and moisture and shear, but with a lot of CIN — boohoo. My expectations remain fairly low. We’ll drift NW on 212, but I’m also keeping an eye on the heavier stuff moving NE into the Black Hills.

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The severe-warned cell that is approaching Rapid City looks anemic on radar—apparently it is a high-based junky thing that is spewing outflow and warning-level winds. We will head that way anyway, as I have committed to playing W SD having just booked 15 rooms in Mobridge.

Rapid City doppler radar shows an outflow boundary moving WNW from the earlier convection that moved into SD from Cherry County. This boundary passed through Philip at 0015Z and it may interact with the storm moving out of the Black Hills in an hour or so. We will need some massive surface convergence to force a surface-based parcel through the cap northeast of RAP…perhaps an outflow boundary collision will do the trick.

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We wound up on some marginally interesting activity northeast of Rapid City.  My chase account:

Our group left Fort Morgan mid-morning, unsure where to target along the E-W CAPE axis from Billings to north of the Black Hills. The strong upper level/negative tilt trough was timed a bit late, and convection was not expected until near or after sunset (if at all) in SE MT. Given this and that we wanted to chase the system east towards ND/MN the following day, I decided to forget about the Billings-area (near the surface low) and to hope for something strong N or NE of the Black Hills. Some high-based junky stuff formed in NE WY and moved over the Black Hills towards RAP, and we intercepted it along 34 around Union Center. There were occasional heavy cores, and it was warned for strong outflow winds. An inflow band from the NE persisted for a while and the leading edge exhibited some structure. A shallow lowered area developed on the leading edge, but overall the base was high and the storm was undercut by its outflow.

It weakened towards Faith, but sporadic lightning activity kept us awake along the empty western SD roads. Brian and I managed some photos of the “tower lighting” effect with multiple “strobe” branches from a tall tower near Faith. At our pit stop in Faith, dust was getting kicked up and the temperature was 91F (in light rain) at 04Z due to heat burst effects.

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So, a day with some decent prospects wound up rather so-so.  An impressive supercell did indeed develop near Billings, with some sheriff-nado reports from 03Z to 04Z.  Here are the images from Union Center to Faith, SD: