Aspects of the May 13/14 th northern high plains Derecho

Aspects of the May 13/14th northern high plains Derecho

Jeffry S. Evans

Storm Prediction Center

10/10/07

Overview

• Derecho-producing MCS- 66 severe wind reports/wind damage along with 6 significant wind reports measured up to 75 mph.

• Severe and near severe winds extended swd for nearly 100 mi south of main convection.

Quick OverviewQuick Overview

• Strong, progressive shortwave trough moving across nrn Rockies.

• E-W surface cold front moving swd across ern MT through the day.

• Moderate instability and strong effective bulk-shear develop ahead of and just behind front.– Low and deep layer shear strengthens in E-

NE surface flow behind front.

GOES-W IR12z (5/13) – 08z (5/14)

SHR- 45G55 0145z

BYG- 40G54 0232z

RAWS site M60 mph 0350z

E60 mph 0430z

RAP- 35G48 0652z

Environment

21z

23z

01z

03z

2150z

2153z BIL 04020G26

2223z

2253z

2323z

2353z

2340z BIL PK WND 36043

0030z

0053z

0123z

0148z SHR 31037G520153z SHR 31045G55

0150z

Conclusions/QuestionsConclusions/Questions

• Appears convective cold pool enhanced cold front, surging front ssewd.

• Strong capping limited new thunderstorm development into MT, but not into ND.

• Measured wind gusts were amplified along eastern slopes of Big Horn mountains and Black Hills.– Blocking effect enhanced frontal surge?

Conclusions/QuestionsConclusions/Questions

• WFOs Billings and Riverton both addressed wind threat with short term forecasts.

• WFO Rapid City used severe thunderstorm warnings.

• How should the NWS handle these events with current product suite?

The EndThe End