Sunday, June 21, 2015

6/19/2015 Moorcroft, WY LP Supercell

Friday featured anomalously high dewpoints for northeast WY and adjacent areas of southeast Montana for severe convection.  Awaking in Miles City, MT, we drifted (took a gravel road shortcut ;]) south toward Gillette, WY.  We met up with the CoD crew to launch a radiosonde from Gillette (data posted below).  The sonde launch was telling, mostly because of the high LCL/LFC of the environment sampled (due to very high T/Td spreads), expressing the low likelihood of tornado producing thunderstorms.  Given this, we chose to stay near GCC and await a nice TCu signal just to our west along the Bighorn Mountains.  This cell eventually matured into a beautiful LP supercell near Moorcroft, WY (see timelapse below).

As our LP began to decay (see RADAR loop), we pushed east toward Spearfish with hopes that a long lived cell originating in the Broadus, MT area would be able to reach the better surface moisture/winds and become tornadic.  Now east of Rapid City, this storm became significantly tornadic with strong gate-to-gate shear and a CC debris signature noted on RADAR.  We stayed ahead of this storm until our hotel location of Wall, SD, with a few in between to take in the majestic storm.  We took shelter in Wall as the storm hit, knocking out power to the entire town with large hail and winds reported near 90 mph.  Definitely a night I will never forget!

MISC: Overnighted (with no power) at the Frontier Cabins in Wall, SD.

Morning severe weather target forecast
Verification of severe weather reports
College of DuPage NEXLAB radiosonde launch from KGCC (21 UTC)
MLCAPE (colored contours) and visible satellite. Our position is the green 'x'
200 image RADAR loop from KUDX (Rapid City, SD)
A rare 'PDS' T-storm watch from the Storm Prediction Center
LP Supercell near Moorcroft, WY
Monster tornadic supercell after dark northwest of Wall, SD

LP supercell lapse

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