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Overview of the Severe Weather Events and NSSL Experiments on 24 May 2011

This document summarizes the key meteorological factors contributing to the severe weather events on May 24, 2011, including the sequence of storm evolution and associated tornadoes in Oklahoma. The left exit region of a jet max within a negatively tilted trough, dryline interactions, and significant moisture advection were critical. The development of extreme instability and exceptional vertical wind profiles resulted in the formation of supercells and multiple tornadoes, including notable EF ratings. The report also discusses experimental data assimilation techniques utilized by the NSSL for improving storm predictions.

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Overview of the Severe Weather Events and NSSL Experiments on 24 May 2011

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  1. Overview of 24 May 2011 Case & NSSL ExperimentsCorey Potvin1,2, Thomas Jones1,2, Dusty Wheatley1,2, Louis J. Wicker21Cooperative Institute for Mesoscale Meteorological Studies2NOAA/OAR National Severe Storms Laboratory

  2. Synoptically evident event • Left exit region of jet max within negatively tilted shortwave trough  strong large-scale ascent • Advancing dryline provided additional lift • Rapid moisture advection from Gulf, aided by southerly flow induced by strong low over OK panhandle • Extreme instability (ML CAPE 3000-4000 J/kg) • Exceptional vertical wind profiles

  3. 500 hPa 0000 Z Surface 1925 Z

  4. Day 2 06 UTC (from 23 May) Day 1 13 UTC

  5. 18 UTC Norman RAOB Fig. 3, Fierro et al. (2012)

  6. Chronology • Dryline initiation ~19 UTC, rapid supercell formation • As low-level jet intensifies, 0-1 km SREH > 300 m2s-2 • Tornadoes develop 2030-2230 UTC and race NE toward OKC metro • Storms weaken as they approach I-35, possibly due to increasing convective inhibition

  7. Storm evolution – MRMS dBZ 2 km AGL 1920 Z 1950 Z 1850 Z 2050 Z 2120 Z 2020 Z

  8. Tornado Paths Canton Lake EF-3 (2015-2043) NSSL-WoF nearly suffers a “setback” Lookeba EF-3 (2031-2046) / El-Reno EF-5 (2050-2235) Goldsby EF-4 (2226-2305) Chickasha EF-4 (2209-2300) 11 fatalities, 293 injuries Adapted from http://www.srh.noaa.gov/oun/?n=events-20110524

  9. Mesoscale DA – GEFS-based NME • Dusty will give more details • WRFv3.4.1; Δ=15 km; 51 levels; 36 members • 1-way 3-km nest – used to initialize storm-scale DA

  10. Storm-scale DA • WRF v3.4.1; Δ=3km; 51 levels; Thompson microphysics • DART-EAKF or NSSL-LETKF • 36 members; 5-min cycles starting ~1845 UTC • Vr, dBZ from KTLX, KVNX, KFDR (OPAWS: Δ=6km) • Objective QC (Chris Karstens web tools) • “no-precip” obs: dBZ < 10 set to 0 • 3 m/s & 5 dBZ errors • Mesonetu, v, T, TD (errors: 1.75 m/s, 1.75 K) • Additive noise (0.5 m/s, 0.5 K) and adaptive inflation • Covariance localization cutoffs: 18 km / 6 km

  11. NSSL Projects • All use mostly the same settings • Dusty – dBZ-based dw/dt forcing • Corey – Running-In-Place • Thomas – satellite DA

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