Storm-scale data assimilation and ensemble forecasting for Warn-on-

Forecast

5th Warn-on-Forecast Workshop

Dusty Wheatley1, Kent Knopfmeier2, and David Dowell3

1,2Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, and NOAA/National Severe Storms Laboratory, Norman Oklahoma

3NOAA/Earth Systems Research Laboratory, Boulder, Colorado

2 April 2014

Work highlights

1) Move to a GEFS-based NSSL Mesoscale Ensemble (NME)

– Provides for a regional convection-allowing (grid spacing ~3 km) ensemble on which to perform radar DA

1) Baseline EnKF experiment for 24 May 2011 using NME background

1) New initialization techniques + radar DA

– Convective initiation/suppression using an updraft nudging technique

NSSL Mesoscale Ensemble (NME)

• Currently: Regional convection-allowing grid (spacing 3 km) is event dependent• Ongoing work to consider the use of a single grid with horizontal spacing of 3 km

Retrospective work:

• 27 April 2011– Spring tornado outbreak– Southeastern United States

• 24 May 2011– Warm season tornadic event– Central Oklahoma

• 17 November 2013– Cool season tornadic event– Midwestern United States

24 May 2011 Tornadic Event

• First tornado reports in Oklahoma between 2015 – 2043 UTC

Ensemble description

• WRF-ARW v3.4.1

• 36-member ensemble, with physics diversity (same for storm-scale ensemble)

– Microphysics: Thompson– Cumulus: Kain-Fritsch, Grell, Tiedtke– Radiation (LW/SW): RRTM/Dudhia, RRTMG/RRTMG– PBL: YSU, MYJ, MYNN

• IC/BCs for *both* parent/nested grids downscaled from 21-member Global Ensemble Forecast System (GEFS) at 0000 UTC 24 May 2011

– No IC/BC perturbations

• Parent/nested grids run simultaneously—from 0000 UTC—in a 1-way nest setup

– Only information exchange occurs at nest’s lateral boundary

Mesoscale data assimilation

• EnKF approach encoded in the Data Assimilation Research Testbed (DART)

• ‘Conventional’ observations (METAR, marine, radiosonde, ACARS, satellite-derived winds) assimilated every 1 h until 0300 UTC 25 May 2011

• Mesonet data assimilation on nested grid only

• No radar data assimilation in producing backgrounds

Ensemble-mean specific humidity at 1800 UTC

• System coupled with either NOAH or RAP land surface models

Dryline

Model soundings at 1800 UTC

• Near convective initiation • At KOUN in Norman, OK

Storm-scale experiments

• Start on nested grid at 1900 UTC

• Assimilate radial velocity and reflectivity (and mesonet) data every 5 min through the period 1900 – 2030 UTC– Frederick (KFDR), Vance Air Force Base (KVNX), and Twin Lakes (KTLX)

WSR-88D’s

• Cleaned radar data objectively analyzed to 6-km grid using Observation Processing and Wind Synthesis (OPAWS)

• Additive noise (T, Td, u, v) where refl. obs. indicate precip.

• Launch 1-h storm-scale ensemble forecasts (with no assimilation) at 2000 and 2030 UTC 24 May

• All plots displayed at 1.5 km AGL

Probability of REFL > 40 dBZ at 1.5 km AGLTop row: 1-h FCST init. @ 2000 UTC

Bottom row: 1-h FCST init. @ 2030 UTC

Vorticity swaths

• Probability of low-level (below ~2 km) vorticity exceeding some threshold; calculated every 5 min during 1-h forecast period

• Maximum probability value retrieved at each model gridpoint

Canton Lake EF-3, 2015-2043Lookeba EF-3, 2031-2046El Reno EF-5, 2050-2235

Forecast cold pools

• Ensemble mean 2-m temp. field calculated every 5 min during forecast period• Minimum 2-m temp. value retrieved at each model gridpoint

Updraft nudging technique

• In the manner of Naylor and Gilmore (2012)

• Modification to w tendency fields in the model

• Use radar reflectivity observations from the NSSL National Mosaic to automatically select where to:– initiate observed storms that are absent in the model forecasts – suppress unobserved regions of simulated storms– REFL obs. swapped out every 10 min

• Ultimately, a complement (not a substitute) to radar DA, similar to additive noise

No wforce

No wforce

With wforce

Vorticity swaths (1915-2015 UTC)

Probability of REFL > 40 dBZ at 1.5 km AGL25-min fcst valid 1940 UTC

Vorticity swaths (1930-2030 UTC)

Ongoing Work

• Collective evaluation of backgrounds generated for earlier listed cases, and severe events during the period 15 – 31 May 2013– Impact of choice of land surface model

• Impact of horizontal resolution, microphysics, etc. on storm-scale results

• Further investigate the use of updraft nudging technique within ensemble-based framework

• Use the Gridpoint Statistical Interpolation (GSI) software for preprocessing observations and computing prior ensemble estimates