THE WINTER STORM RECONNESSAINCE PROGRAM OF THE US NATIONAL WEATHER SERVICE

1. Zoltan Toth GSD/ESRL/OAR/NOAA Formerly at EMC/NCEP/NWS/NOAA Acknowledgements: Yucheng Song – Plurality at EMC Sharan Majumdar – U. Miami Istvan Szunyogh – Texas AMU Craig Bishop - NRL Rolf Langland - NRL THORPEX Symposium, Sept 14-18 2009, Monterey, CA THE WINTER STORM RECONNESSAINCE PROGRAM OF THEUS NATIONAL WEATHER SERVICE

2. OUTLINE / SUMMARY • History • Outgrowth of FASTEX & NORPEX research • Operationally implemented at NWS in 2001 • Contributions / documentation • Community effort • Refereed and other publications, rich info on web • Highlights • Operational procedures for case selection, ETKF sensitivity calculations • Positive results consistent from year to year • Open questions • Does operational targeting have economic benefits? • Can similar or better results be achieved with cheaper obs. systems? • What are the limitations of current techniques?

3. HISTORY OF WSR • Sensitivity calculation method • Ensemble Transform (ET) method developed around 1996 • Field tests • FASTEX – 1997, Atlantic • Impact from sensitive areas compared with that from non-sensitive areas (“null” cases) • NORPEX – 1998, Pacific • Comparison with adjoint methods • CALJET, PACJET, WC-TOST, ATReC, AMMA, T-PARC • WSR • 1999 - First test in research environment • 2000 - Pre-implementation test • 2001 - Full operational implementation

4. CONTRIBUTIONS • Craig Bishop (NASA, PSU, NRL) • ET & ETKF method development • Sharan Majumdar (PSU, U. Miami) • ETKF method development and implementation • Rolf Langland (NRL), Kerry Emanuel (MIT) • Field testing and comparisons in FASTEX, NORPEX, TPARC • Istvan Szunyogh (UCAR Scientist at NCEP, U. MD, Texas AMU) • Operational implementation, impact analysis, dynamics of data impact • Yucheng Song (Plurality at EMC/NCEP/NWS/NOAA) • Updates, maintenance, coordination • Observations • NOAA Aircraft Operations Center (G-lV) • US Air Force Reserve (C130s) • Operations • Case selection by NWS forecasters (NCEP/HPC, Regions) • Decision making by Senior Duty Meteorologists (SDM)

5. DOCUMENTATION • Papers (refereed / not reviewed) • Methods • ET Bishop & Toth • ETKF Bishop et al, Majumdar et al • Field tests • Langland et al FASTEX • Langland et al NORPEX • Szunyogh et al FASTEX • Szunyogh et al NORPEX • Song et al TPARC (under preparation) • Operational implementation • Toth et al 2 papers • WSR results • Szunyogh et al • Toth et al (under preparation) • Web • Details on procedures • Detailed documentation for each case in WSR99-09 (11 years, ~200+ cases) • Identification of threatening high impact forecast events • Sensitivity calculation results • Flight request • Data impact analysis

6. OPERATIONAL PROCEDURES • Case selection • Forecaster input – time and location of high impact event • Based on perceived threat and forecast uncertainty • SDM compiles daily prioritized list of cases for which targeted data may be collected • Ensemble-based sensitivity calculations • Forward assessment • Predict impact of targeted data from predesigned flight tracks • Backward sensitivity • Statistical analysis of forward results for selected verification cases • Decision process • SDM evaluates sensitivity results • Consider predicted impact, priority of cases, available resources • Predesigned flight track # or no flight decision for next day • Outlook for flight / no flight for day after next • Observations • Drop-sondes from manned aircraft flying over predesigned tracks • Aircraft based in Alaska (Anchorage) and/or Hawaii (Honolulu) • Real time QC & transmission to NWP centers via GTS • NWP • Assimilate all adaptively taken data along with regular data • Operational forecasts benefit from targeted data

7. HIGHLIGHTS • Case selection • No systematic evaluation available • Some errors in position / timing of threatening events in 4-6 day forecast range • Affects stringent verification results • Need for objective case selection guidance based on ensembles • Sensitivity calculations • Predicted and observed impact from targeted data compared in statistical sense • Sensitivity related to dynamics of flow • Variations on daily and longer time scales (regime dependency) • Decision process • Subjective due to limitations in sensitivity methods • Spurious correlations due to small sample size • Observations • Aircraft dedicated to operational observing program used • Are there lower cost alternatives? • Thorough processing of satellite data • UAVs? • NWP forecast improvement • Compare data assimilation / forecast results with / without use of targeted data • Cycled comparison for cumulative impact • One at a time comparison for better tracking of impact dynamics in individual cases

8. Observed data impact Predicted data impact Forecastimprovement / degradation

9. WHY TARGETING MAY WORK Impact of data removal over Pacific - Kelly et al. 2007 Figure 1. Winter Pacific forecasts: Verification of mean 500 hPa geopotential rmse up to day 10 for SEAOUT in grey dotted and SEAIN in black: Both experiments are verified using ECMWF operational analysis. Verification regions: (a) North Pacific, (b) North America, (c) North Atlantic and (d) the European region.

10. FORECAST EVALUATION RESULTS Based on 10 years of experience (1999-2008) • Error reduced in ~70% of targeted forecasts • Verified against observations at preselected time / region • Wind & temperature profiles, surface pressure • 10-20% rms error reduction in preselected regions • Verified against analysis fields • 12-hour gain in predictability • 48-hr forecast with targeted data as skillful as 36-hr forecast without

11. WSR Summary statistics for 2004-07 Wind vector error, 2007 25+22+19+26= 92 POSITIVE CASES 0+1+0+0 = 1 NEUTRAL CASE 10+7+8+11 = 36 NEGATIVE CASES 71.3% improved 27.9% degraded OVERALL EFFECT: Without targeted data With targeted data

12. Valentine’s day Storm2007 • Weather event with a large societal impact • Each GFS run verified against its own analysis – 60 hr forecast • Impact on surface pressure verification • RMS error improvement: 19.7% • (2.48mb vs. 2.97mb) • Targeted in high impact weather area marked by the circle Surface pressure from analysis (hPa; solid contours) Forecast Improvement (hPa; shown in red) Forecast Degradation (hPa; blue)

13. Average surface pressure forecast error reduction from WSR 2000 The average surface pressure forecast error reduction for Alaska (55°–70°N, 165°–140°W), the west coast (25°–50°N, 125°–100°W), the east coast (100°–75°W), and the lower 48 states of the United States (125°–75°W). Positive values show forecast improvement, while negative values show forecast degradation (From Szunyogh et al 2002)

14. Forecast Verification for Wind (2007) 10-20% rms error reduction in winds Close to 12-hour gain in predictability RMS error reduction vs. forecast lead time

15. Forecast Verification for Temperature (2007) 10-20 % rms error reduction Close to 12-hour gain in predictability RMS error reduction vs. forecast lead time

16. CONCLUSIONS • High impact cases can be identified in advance using ensemble methods • Data impact can be predicted in statistical sense using ET / ETKF methods • Optimal observing locations / times for high impact cases can be identified • It is possible to operationally conduct a targeted observational program • Open questions remain

17. OPEN QUESTIONS • Does operational targeting have economic benefits? • Cost-benefit analysis needs to be done for different regions – SERA research • Are there differences between Pacific (NA) & Atlantic (Europe)? • Can similar or better results be achieved with cheaper observing systems? • Observing systems of opportunity • Targeted processing of satellite data • AMDAR • UAVs? • Sensitivity to data assimilation techniques • Advanced DA methods extracts more info from any data • Better analysis without targeted data • Larger impact from targeted data (relative to improved analysis with standard data)? • What are the limitations of current techniques? • What can be said beyond linear regime? • Need larger ensemble for that? • Can we quantify expected forecast improvement (not only impact)? • Distinction between predicting impact vs. predicting positive impact • Effect of sub-grid scales ignored so far • Ensemble displays more orderly dynamics than reality? • Overly confident signal propagation predictions?

18. DISCUSSION POINTS How to explain large apparent differences between various studies regarding effectiveness of targeted observations? • Case selection important • Only every ~3rd day there is a “good” case • Targeting is not cure for all diseases • If all cases averaged, signal washed out at factor of 1/3 • Measure impact over target area • Effect expected in specific area • If measured over much larger area, signal washes out by factor of 1/3 • 2 factors above may explain 10-fold difference in quantitative assessment of utility in targeting observations • Not all cases expected to yield positive results • Artifact of statistical nature of DA methods • Should expect some negative impact • Current DA methods lead to forecast improvements in 70-75% of cases • Geographical differences • Potentially larger impact over larger Pacific vs smaller Atlantic basins?

19. BACKGROUND

20. Example: Impact of WSRP targeted dropsondes Binned Impact 1 Jan – 28 Feb 2006 00UTC Analysis Beneficial (-0.01 to -0.1 J kg-1) Non-beneficial (0.01 to 0.1 J kg-1) NOAA-WSRP 191 Profiles Small impact (-0.01 to 0.01 J kg-1) Average dropsonde ob impact is beneficial and ~2-3x greater than average radiosonde impact

21. Composite summary maps 139.6W 59.8N 36hrs (7 cases) - 1422km 92W 38.6N 60hrs (5 cases)- 4064km 80W 38.6N 63.5hrs (8 cases) - 5143km 122W 37.5N 49.5hrs (8 cases) - 2034km Verification Region Verification Region

22. North Pacific observation impact sum - NAVDAS Change in 24h moist total energy error norm (J kg-1) 1-31 Jan 2007 (00UTC analyses) Error Reduction

23. North Pacific forecast error reductionper-observation Change in 24h moist total energy error norm (J kg-1) 1-31 Jan 2007 (00UTC analyses) Error Reduction (x 1.0e5) Ship Obs Targeted dropsondes = high-impact per- ob, low total impact

24. ETKF predicted signal propagation

25. ETS 5mm 10mm 16.35 18.56 CTL 16.50 20.44 OPR Positive vs. negative cases 4:1 3:1 Precipitation verification • Precipitation verification is still in a testing stage due to the lack of station observation data in some regions.