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TDL WORKSHOP ON MOS INTERPRETIVE GUIDANCE

TDL WORKSHOP ON MOS INTERPRETIVE GUIDANCE. J. Paul Dallavalle paul.dallavalle@noaa.gov 301-713-1065, ext. 174 Mary C. Erickson mary.erickson@noaa.gov 301-763-8151 http://www.nws.noaa.gov/tdl/synop March 31, 2000. OUTLINE. Why Interpretive Guidance? Sample Guidance Products

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TDL WORKSHOP ON MOS INTERPRETIVE GUIDANCE

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  1. TDL WORKSHOP ON MOS INTERPRETIVE GUIDANCE J. Paul Dallavalle paul.dallavalle@noaa.gov 301-713-1065, ext. 174 Mary C. Erickson mary.erickson@noaa.gov 301-763-8151 http://www.nws.noaa.gov/tdl/synop March 31, 2000

  2. OUTLINE • Why Interpretive Guidance? • Sample Guidance Products • MOS Defined • Developmental Strategy • Use of Guidance • New MOS Products • Verification - The Future

  3. REFERENCES • Wilks,D.: Statistical Methods in the Atmospheric Sciences, Chap. 6, p. 159 -210. • Glahn, H.R., and D. Lowry, 1972: The use of model output statistics in objective weather forecasting, JAM, 11, 1203 -1211. • Draper, N.R., and H. Smith, Applied Regression Analysis, Chap. 6, p. 307 - 308. • Carter, G.M., et al., 1989: Statistical forecasts based on the NMC’s NWP System, Wx. & Fcst., • p. 401 - 412.

  4. WHY INTERPRETIVE GUIDANCE? • Assist forecasters • “First Guess” for expected local conditions • “Built-in” model/climo memory for new staff • Add value to direct NWP model output • Objectively interpret model to remove systematic biases and quantify uncertainty • Predict what the model does not • Produce site-specific forecasts

  5. MODEL OUTPUT STATISTICS • Technique in which observed weather elements (predictands) are related statistically to appropriate predictor variables: • NWP Model Forecasts • Prior Surface Weather Observations • Geoclimatic Information

  6. MODEL OUTPUT STATISTICS More Essentials • Current method: Multiple linear regression (forward selection) • Mathematically simple, yet powerful • Non-linearity modeled by NWP variables, grid binaries, variable transformations • Other statistical methods possible, e.g., logistic regression, polynomial regression, neural networks, etc. • Equations applied to similar NWP model

  7. MODEL OUTPUT STATISTICS • Advantages • Optimal predictor selection • Recognition of model predictability • Removal of some systematic bias • Reliable probabilities • Specific element and site forecasts • Disadvantages • Short samples • Changing NWP models

  8. DEVELOPMENTAL STRATEGY • Predictand Definition • Choice of Appropriate Predictors • Sample Size • Terms in Equations • Stratification of Developmental Data - Seasons • Pooling of Developmental Data - Regions • Overfit of Data

  9. PREDICTAND DEFINITIONS Examples • Daytime max temperature: 7am-7pm LST • Nighttime min temperature: 7pm-8am LST • Probability of precipitation (PoP): occurrence of 0.01 inches of liquid equivalent at the gauge within a specified period

  10. PREDICTORS • Describe physical processes associated with occurrence of predictand • PoP: use precipitable water, vertical velocity, moisture divergence, model precipitation • Mimic forecasters’ thought process • PoP: (vertical velocity) × (mean RH)

  11. “REAL” REGRESSION EQUATIONS MOS regressions equations are MULTIVARIATE: Y = a0 + a1X1 + a2X2 + ... + aNXN, where the “ai’s” represent coefficients, and the “Xi’s” represent predictors The maximum number of terms, N, can be QUITE large, e.g., N=15 for QPF, and N=20 for VIS FORWARD SELECTION regression determines the predictors and the order of selection.

  12. PTYPE DEVELOPMENT REGIONS

  13. CURRENT NGM/MRF MOS A Summary • NGM MOS predictors valid at 6-h intervals to 48h; NGM MOS valid to 60h • MRF MOS predictors valid at 12-h intervals to 192h; MRF MOS valid to 192h • NGM MOS predictors on 190.5 km grid; MRF MOS predictors on 381 km grid • NGM MOS predictors at 50-mb resolution in vertical; MRF MOS predictors at mandatory levels

  14. MOS USER TIPS • Inconsistent forecasts occur, especially with categorical elements - check spatial/temporal continuity • Seemingly inconsistent forecasts occur - do you know the predictand definition? • Guidance may be too conservative during persistent abnormal weather patterns • Systematic errors occur with certain “map types” • Guidance does not predict mesoscale events • Regionalized guidance may not account for local effects • NGM/AVN MOS depend on different samples and different models with different initial conditions and physics packages

  15. MOS-2000 What Does It Mean to the Customer? • Enhanced AVN MOS for Short-Range • First phase: NGM MOS look-alike • Guidance to 72 h • 1000+ stations • Enhanced MRF MOS for Medium-Range • New forecast elements • Revised element definitions • Same stations as short-range • Eta MOS for Storm-Related Elements

  16. NEW AVN MOS GUIDANCE A Different Look • Available for 1000+ Sites in CONUS, AK, HI, PR • Predictands from Current Observing System • Predictands to 72 h • Model Predictors from 95.25 km Grid • Model Predictors valid every 3 h to 72 h • 0600 / 1800 UTC AVN MOS Packages

  17. NEW AVN VS. NGM MOS GUIDANCE What to expect? • AVN MOS may be more accurate with max/min, dew point, clouds, PoP, winds • NGM MOS may be more accurate with some temperatures, ceiling height, precip. type, some QPF • Differences are small • http://www.nws.noaa.gov/synop/results.htm

  18. NEW MRF MOS GUIDANCE A Different Look • Available for 1000+ Sites in CONUS, AK, HI, PR • New Weather Element Definitions • Wind, clouds, precip. type • Additional Weather Elements • Temperature, dew pt., QPF, thunderstorms, snowfall

  19. NEW MRF MOS GUIDANCE Unchanged • Forecast projections to 192 h • Daytime max temp (7am - 7pm LST) • Nighttime min temp (7pm - 8am LST) • Probability of .01 inches in 12-h period (PoP)

  20. NEW MRF MOS GUIDANCE Additions • Temp./dew pt. every 6 h from 18 to 192 h • PQPF for 12- and 24-h periods • Categories: 0.10, 0.25, 0.50, 1.00, 2.00 in • Prob. of thunderstorms for 12- and 24-h periods to 192 h • Prob. of 24-h snowfall amounts • Categories: 1, 2, 4, 6, 8, 10 inches

  21. NEW MRF MOS GUIDANCE Changes • Prob. of prevailing sky cover in 12-h period • Categories: clear, partly cloudy, overcast • Prob. of max. sustained hourly wind speed in 12- h period • Categories: 10 kts, 11-21 kts, 22-34 kts, 35 kts • Conditional prob. of precip. type in 12-h period • Categories: liquid, snow, freezing

  22. MOS GUIDANCE Implementation Plans • May 2000 - AVN MOS Message (00Z / 12Z) • May 2000 - New MRF MOS Message • Oct. 2000 - Complete AVN MOS (No Snow) • Oct. 2000 - Complete MRF MOS (No Snow) • Oct. 2000 - Eta MOS Thunderstorm Guidance • Apr. 2001 - NGM MOS Discontinued ? • Apr. 2001 - Old AVN/MRF MOS Discontinued

  23. MOS GUIDANCE Do I use this tool? • Modify the WFO forecast according to my interpretation of MOS • Modify MOS according to my analysis of all available information • Compare MOS packages • ABSOLUTELY NOT!! • WITHOUT QUESTION!!

  24. MOS Future Enhancements • Frequent equation updates • Increased accuracy • More stations • Additional predictands • Dissemination in digital format • Complete AVN MOS package 4x daily • New techniques

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