# Presentation: 124574

## Use of High-Resolution WRF Simulations to

**Use of High-Resolution WRF Simulations to**
**Forecast Lightning Threat**

- Photo, David Blankenship
- Guntersville, Alabama

**E. W. McCaul, Jr.****1****, K. La Casse****2****, S. J. Goodman****3****, **
**and D. J. Cecil****2**
- 1: USRA Huntsville
- 2: University of Alabama in Huntsville
- 3: NASA Marshall Space Flight Center
- Huntsville, Alabama, USA

- SPoRT Meeting
- 14 February 2007

## Premises and Objectives

- WRF: Weather Research and Forecast Model
- CRM: Cloud Resolving Model

- _Additional Forecast Interests_
- CI - convective initiation
- Ti  - First lightning (35 dBZ at -15C, glaciation)
- Tp - Peak flash rate  VIL (Mass)
- Tf  - Final lightning

- Given:
- Precipitating ice aloft is correlated with LTG rates
- Mesoscale CRMs are being used to forecast convection
- CRMs can represent many ice hydrometeors (crudely)
- Goals:
- Create WRF forecasts of LTG threat, based on ice flux
-       in layers near -15 C, and on simulated reflectivity.

## Flash Rate Coupled to Mass in the Mixed Phase Region

**Flash Rate Coupled to Mass in the Mixed Phase Region**
**Cecil et al., Mon. Wea. Rev. 2005 (from TRMM Observations)**

##   - Pr (CPTP) >= 1 x Pr (PCPN) >= .01”

**F15 SREF 3-hr COMBINED**
**PROBABILITY OF LIGHTNING**

-   **- Pr (CPTP) >= 1 x Pr (PCPN) >= .01”**

**Uncalibrated probability**
**of lightning**

- SPC Experimental Product

## WRF Lightning Threat Forecasts:Methodology 

- Use high-resolution (2-km) WRF simulations to prognose
-       convection
- Develop diagnostics from model output fields to serve as
-       proxies for LTG: graupel fluxes; reflectivity profiles
- Create 0-6, 0-8 or 0-12 h forecasts of LTG threat based on WRF output for the selected diagnostics
- Calibrate WRF forecasts with actual total LTG rates from HSV LMA and reflectivity from TRMM PR radar
- Assess WRF capabilities for forecasting LTG threat

## WRF Lightning Threat Forecasts:10 December 2004Cold-season hailstorms, little LTG 

## WRF Configuration (typical)10 December 2004 Case Study

- 2-km horizontal grid mesh
- 50 vertical sigma levels
- Dynamics and physics:
- Eulerian mass core
- Dudhia SW radiation
- RRTM LW radiation
- YSU PBL scheme
- Noah LSM
- WSM 6-class microphysics scheme (graupel; no hail)
- 8h forecast initialized at 12 UTC 10 December 2004 with AWIP212 NCEP EDAS analysis;
- Also used METAR, ACARS, and WSR-88D radial vel at 12 UTC;
- Eta 3-h forecasts used for LBC’s

## WRF Sounding, 2004121019Z

- Lat=34.8
- Lon=-85.9
- CAPE~500

## LTG ground truth: flash density10 December 2004, 19Z 

## WRF Reflectivity at 1.25 km:10 December 2004 

## LTG threat derived from WRF graupel flux at -15C

- Compute field of upward graupel flux at -15C
- Rescale dynamic range of values against observed LTG flash rates on the same 1 km grid; for experiments looked  at thus far, scale coefficient is ~0.2 (this will change)
- With histogram truncation, could match areal coverage to observations; not done here because of loss of some simulated storms which appear to be important
- After applying scaling factor, obtain field of LTG flash rates in units of fl/(5 min)/km2

## LTG threat methodology advantages

- Method based on LTG physics
- Method supported by solid observational evidence
- Can be used to obtain quantitative estimates of flash rates
- Method is fast and simple; based on basic model output fields; no need for complex electrification modules
- Graupel flux method can be expanded to include a flux threshold, which will allow truncation of flux histogram so as to allow matching of areal coverages of predicted and observed LTG activity, as model accuracy improves

## LTG threat based onWRF graupel flux at -15 C

## WRF Lightning Threat Forecasts:30 March 2002Supercell ahead of Squall Line 

## WRF Sounding, 2002033003Z

- Lat=34.4
- Lon=-88.1
- CAPE~2800

## LTG ground truth: LMA flash rate30 March 2002, 04Z 

## WRF Reflectivity at 1.25 km:30 March 2002, 04Z 

## LTG threat based onWRF graupel flux at -15C

##                                Conclusions:1. On 100 km scales, WRF forecasts of LTG are useful in terms    of location, timing and amplitude2. On 10 km scales, LTG forecasts are only as good as the model3. Inclusion of WSR-88D velocity data helps; so does dBZ if storms                  already up at t=04. WRF microphysics still too simple; need more ice categories;    need double-moment or better microphysics5. Finer model mesh may improve updraft representation, and    hydrometeor amounts6. Biggest limitation is likely errors in initial mesoscale fields

##                                Future Work:1. Expand catalog of simulation cases to obtain better statistics2. Test newer versions of WRF, when available:    - more hydrometeor species    - double-moment microphysics3. Run on 1-km or finer grids, whenever feasible4. In future runs, examine fields of interval-cumulative wmax,    and associated hydrometeor and reflectivity data, not just the    instantaneous values; for save intervals of 15-30 min, events     happening between saves may be important for LTG threat5. Refine dBZ-based LTG threat computation to account for    size of individual storms, not just storm systems6. Assess WRF utility in prognosing LTG onset, cessation

##                           Acknowledgments:This research was funded by the NASA Science Mission Directorate’s Earth Science Division in support of the Short-term Prediction and Research Transition (SPoRT) Project at Marshall Space Flight Center, Huntsville, AL.