1. Performance of the Experimental 4.5 km WRF-NMM Model During Recent Severe Weather Outbreaks Steven Weiss, John Kain, David Bright, Matthew Pyle, Zavisa Janjic and Brad Ferrier

2. Why Examine High Res. WRF Models? Severe weather types (tornadoes, hail, wind damage) can be closely related to convective mode –Tornadoes (discrete supercells) –Damaging wind (bow echoes and QLCSs) SPC working to increase lead time of watches and provide probabilistic information about tornado, hail, and wind threats in Day 1 Severe Weather Outlooks Accurate forecasts require knowledge about “where” and “when” storms will develop and how they will evolve –There is a need to better predict convective mode and character of storms (stormscale details) –Environmental clues (CAPE/shear, etc.) may not be sufficient –Operational mesoscale models often lack smaller scale details

3. NOAA Hazardous Weather Testbed SPC/NSSL Spring Programs Spring Programs in 2004 and 2005 examined various configurations of convection-allowing WRF models –Partnerships with EMC, OU-CAPS, and NCAR –Can high resolution WRF provide useful guidance for severe forecasting? –Since April 2004, EMC has been running an experimental 4.5 km version of the WRF-NMM once daily 36 hour forecasts from 00 UTC start Very large domain (eastern three-fourths of CONUS)

4. High Res. WRF-NMM Configuration (No Parameterized Convection) EMC WRF-NMM4 Horiz. Grid Spacing (km) 4.5 Vertical Levels 35 PBL/Turbulence Param. MYJ Microphysical Param. Ferrier Radiation Param. GFDL Initial/Boundary Conditions 00z 32 km NAM ( see http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/cent4km/v2/)

5. Simulated Reflectivity in WRF Output Simulated Reflectivity Computed from model predicted grid-resolved hydrometeor fields Highly dependent on model physics (especially microphysics) Appealing to forecasters because it closely resembles radar images of precipitation systems Allows identification of mesoscale and stormscale structures Easier to subjectively verify model forecasts by comparing directly with observed radar images

6. Simulated Reflectivity in WRF Output High res WRF reflectivity can provide mesoscale and near stormscale details not seen in traditional output 21 hour forecasts valid 21 UTC 15 Nov 2005 NAM-WRF 3h Pcpn 4.5 km WRF-NMM Reflectivity

7. Simulated Reflectivity in WRF Output Model resolution impacts structural detail, intensity, and realism of simulated reflectivity forecasts 21 hour forecasts 1 km AGL reflectivity valid 21 UTC 20 May 2006 12 km NAM-WRF 4.5 km WRF-NMM

8. Recent Significant Tornado Days DateSevere Reports TornadoesKiller Tornadoes Tornado Fatalities 11/5/052938125 11/15/052434911 11/27/052406722 3/11/062551712 3/12/0666914058 4/02/0687286526 4/07/0687191310

10. 4.5 km WRF-NMM and Radar 31 hr WRF forecast valid 07z 6 Nov 2005 WRF-NMM 1 km AGL Reflectivity Radar F3 tornado 0759z 25 fatalities

12. 4.5 km WRF-NMM and Radar 21 hr WRF forecast valid 21z 15 Nov 2005 WRF-NMM 1km AGL Reflectivity Radar F3 tornado 2030z 1 fatality

13. Comments from SPC Forecasters About November 15 WRF-NMM Guidance “One of the best pieces of information was the WRF-NMM 4 km "equivalent reflectivity" product. This product did a GREAT job of persistently depicting a line of forced convection along the front, along with bands of storms ahead of the main line. With the WRF showing these bands…increasing in intensity by late morning well east of the front, we gained confidence that it would be prudent to go much further e than the frontal zone itself with the early watch.” SPC Midnight Shift Mesoscale Forecaster “The WRF-NMM4 provided very useful input regarding the mesoscale organization and character of storms. While there were certain details that the model missed, it was superb in predicting multiple convective lines and their rough extents. I used it to help delineate where/when watches would be required.” SPC Day Shift Lead Forecaster

15. 4.5 km WRF-NMM and Radar 24hr WRF forecast valid 00z 28 Nov 2005 WRF-NMM 1km AGL Reflectivity Radar F3 Tornado 0015z 1 Fatality

17. 4.5 km WRF-NMM and Radar 27hr WRF forecast valid 03z 12 Mar 2006 WRF-NMM 1km AGL Reflectivity Radar F3 Tornado 0310z 4 Fatalities

18. 4.5 km WRF-NMM and Radar 28hr WRF forecast valid 04z 12 Mar 2006 WRF-NMM 1km AGL Reflectivity Radar F3 Tornado 0310z 4 Fatalities

20. 4.5 km WRF-NMM and Radar 27hr WRF forecast valid 03z 12 Mar 2006 WRF-NMM 1km AGL Reflectivity Radar F3 Tornado 0310z 4 Fatalities

22. 4.5 km WRF-NMM and Radar 25hr WRF forecast valid 01z 3 Apr 2006 WRF-NMM 1km AGL Reflectivity Radar 2 F3 Tornadoes 0056 and 0143z 22 Fatalities

24. 4.5 km WRF-NMM and Radar 18hr WRF forecast valid 18z 7 Apr 2006 WRF-NMM 1km AGL Reflectivity Radar

25. 4.5 km WRF-NMM and Radar 19hr WRF forecast valid 19z 7 Apr 2006 WRF-NMM 1km AGL Reflectivity Radar F3 Tornado 1927z 8 Fatalities

26. 4.5 km WRF-NMM and Radar 20hr WRF forecast valid 20z 7 Apr 2006 WRF-NMM 1km AGL Reflectivity Radar

27. 4.5 km WRF-NMM and Radar 21hr WRF forecast valid 21z 7 Apr 2006 WRF-NMM 1km AGL Reflectivity Radar

28. 4.5 km WRF-NMM and Radar 22hr WRF forecast valid 22z 7 Apr 2006 WRF-NMM 1km AGL Reflectivity Radar

29. 4.5 km WRF-NMM and Radar 23hr WRF forecast valid 23z 7 Apr 2006 WRF-NMM 1km AGL Reflectivity Radar

30. 4.5 km WRF-NMM and Radar 24hr WRF forecast valid 00z 8 Apr 2006 WRF-NMM 1km AGL Reflectivity Radar

31. 4.5 km WRF-NMM Summary On many days the 4.5 km WRF-NMM exhibits credible mesoscale prediction skill of convective systems –Especially during strongly forced situations Current 4.5 km grid length permits “approximation” of stormscale structures –Convective mode details often very helpful Discrete cells, quasi-linear and multicell systems But resolution is too coarse to simulate realistic updrafts –“Large” model updrafts are slower to develop –Not uncommon for model storms to develop 1-2 hours late Key forecaster challenge –Hi Res WRF-NMM forecasts often appear plausible –How do we know when to believe the stormscale details and when to discount them? –Suggests role for high resolution ensembles