TDL WORKSHOP ON MOS INTERPRETIVE GUIDANCE
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Transcript of TDL WORKSHOP ON MOS INTERPRETIVE GUIDANCE
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TDL WORKSHOP ON MOS INTERPRETIVE GUIDANCE
J. Paul Dallavalle
301-713-1065, ext. 174
Mary C. Erickson
301-763-8151
http://www.nws.noaa.gov/tdl/synop
March 31, 2000
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OUTLINE
1. Why Interpretive Guidance?
2. Sample Guidance Products
3. MOS Defined
4. Developmental Strategy
5. Use of Guidance
6. New MOS Products
7. Verification - The Future
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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.
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Projection (Hour)6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72
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AVN MOS
AVN DMO
CONUS and Alaska 00z Apr.1 - Sept.30, 1999
Dew Point Mean Absolute Error
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eg F
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24 48 72 96 120 144 168 192Projection (hours)
NEW MOS CLIMO DMO
MRF MOS Max Temp1999 Warm Season - CONUS/AK
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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
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MODEL OUTPUT STATISTICS
Technique in which observed weather elements (predictands) are related statistically to appropriate predictor variables:
1. NWP Model Forecasts
2. Prior Surface Weather Observations
3. Geoclimatic Information
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MODEL OUTPUT STATISTICS
• 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
More Essentials
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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
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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
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PREDICTAND DEFINITIONS
• 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
Examples
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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)
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“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.
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PTYPE DEVELOPMENT REGIONS
* forecasts will not be produced for stations in the hatched areas
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CURRENT NGM/MRF MOS
• 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
A Summary
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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
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MOS-2000
• 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
What Does It Mean to the Customer?
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NEW AVN MOS GUIDANCE
• 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
A Different Look
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NEW AVN VS. NGM MOS GUIDANCE
• 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
What to expect?
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NEW MRF MOS GUIDANCE
• 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
A Different Look
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NEW MRF MOS GUIDANCE
• 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)
Unchanged
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NEW MRF MOS GUIDANCE
• 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
Additions
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NEW MRF MOS GUIDANCE
• 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
Changes
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MOS GUIDANCE
• 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
Implementation Plans
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MOS GUIDANCE
• 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!!
Do I use this tool?
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MOS
• Frequent equation updates
• Increased accuracy
• More stations
• Additional predictands
• Dissemination in digital format
• Complete AVN MOS package 4x daily
• New techniques
Future Enhancements