understanding individual and ensemble forecast behavior ... l. jensen.pdf · understanding...
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UNDERSTANDING INDIVIDUAL AND ENSEMBLE FORECAST BEHAVIOR USING THE METHOD FOR OBJECT BASED DIAGNOSTIC EVALUATION (MODE)
Tara L. Jensen, Barbara Brown, John Halley Gotway, Tressa Fowler and Randy Bullock National Center for Atmospheric Research, Boulder Colorado, USA and Developmental Testbed Center, Boulder Colorado, USA
6th WMO International Verification Methods Workshop, 17-19 March 2014 ° New Dehli, India
Contributions from Marion Mittermeyer (UKMet Office), Wallace Clark (NOAA/Physical Science Division, Edward Tollerud (NOAA/Global Science Division and Adam Clark (NOAA/National Severe Storms Laboratory)
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OVERVIEW • How MODE Works
• Evaluating individual model performance • Examples and results
• Diagnosing ensemble performance • New research
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MODEL EVALUATION TOOLS (MET)
Gridded NetCDF
Gridded GRIB Input:
Observation
Analyses
Model Forecasts
PrepBufr Point Obs
STAT
NetCDF Point Obs
ASCII NetCDF
PS
STAT ASCII
NetCDF
Input Reformat Statistics
= optional
ASCII
ASCII Point Obs
Wavelet Stat
STAT ASCII
NetCDF PS
NetCDF Mask
Analysis
MODE
Grid Stat
Ensemble Stat
Point Stat
MODE Analysis
Stat Analysis
PCP Combine
Gen Poly Mask
STAT ASCII
NetCDF
ASCII
MADIS Point Obs
ASCII2NC
PB2NC
MADIS2NC
Developed by the Developmental Testbed Center, Boulder Colorado, USA
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MODE OBJECT DEFINITION
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OBJECT ORIENTED METHOD: MODE HOW IT WORKS
OBS ENS FCST Radius=5
ObjectThresh >6.35 mm
MergingThresh > 5.7 mm
Radius=5
ObjectThresh >6.35 mm
MergingThresh >5.7 mm
Merging
Matching
No false alarms
Misses
Merging
Matched Object 1 Matched Object 2 Unmatched Object
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EXAMPLE – REFC > 30 DBZ – MODE OBJECTS Convolution Radius Increases
FSS = 0.64
Total Interest: 0.96 Area Ratio: 0.57 Centroid Distance: 95km P90 Intensity Ratio: 1.00
Total Interest: 0.96 Area Ratio: 0.57 Centroid Distance: 94km P90 Intensity Ratio: 1.02
Total Interest: 0.96 Area Ratio: 0.53 Centroid Distance: 92km P90 Intensity Ratio: 1.04
3 gs
9 gs
15 gs
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USE OF ATTRIBUTES OF OBJECTS DEFINED BY MODE
Centroid Distance: Provides a quantitative sense of spatial Displacement. Small is good
Forecast Field
Observed Field
Axis Angle: Provides an objective measure of how well the objects are aligned. Small is good
Area Ratio: Provides an objective measure of whether there is an over- or under- prediction of areal extent. Close to 1 is good
Obs Area
Fcst Area
Area Ratio = Fcst Area Obs Area
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5/14/2010
Symmetric Diff: May be a good summary statistic for how well Forecast and Observed objects match. Small is good
Forecast Field
Observed Field
P50/P90 Int: Provides objective measures of Median (50th percentile) and near-Peak (90th percentile) intensities found in objects. Ratio close To 1 is good
Total Interest: Summary statistic derived from fuzzy logic engine with user-defined Interest Maps for all these attributes plus some others. Close to 1 is good
Symmetric Difference: Non-Intersecting Area
Fcst PWT P50 = 29.0 P90 = 33.4
Obs IWV*10 P50 = 26.6 P90 = 31.5
Total Interest 0.75
USE OF ATTRIBUTES OF OBJECTS DEFINED BY MODE
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MODE IN USE
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6HR ACCUMULATED PRECIPITATION NEAR PEAK (90TH%) INTENSITY DIFFERENCE
D
iffer
ence
(P90
Fcs
t – P
90 O
bs)
High Resolution Deterministic Does Fairly Well
High Resolution Ensemble Mean Underpredicts
Mesoscale Deterministic Underpredicts
Mesoscale Ensemble Underpredicts the most
Overforecast
Underforecast
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Impact of Core & Microphysics
90% Intensity shows over- forecast of precipitation for ARW-Fer and ARW-MY members especially at higher thresholds – which means when it rains it pours in these members
> 25.4mm
Diffe
renc
e (F
cst-
Obs
) in
Nea
r Pea
k In
tens
ity in
MO
DE O
bj (m
m)
Object Threshold (mm)
NMM ARW
HMT NAM GFS
Using Attributes from MODE Objects
Color groups Different Microphysics
Ferrier Milbrant-Yau Thompson
Intense Cores
Optimal
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RADAR ECHO TOPS FOR AVIATION DESK
WRF Members with Different Microphysics Schemes
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RADAR ECHO TOPS – SYMMETRIC & CENTROID DIFFERENCE
Symmetric Difference diverse Centroid Difference not Probably an over-forecast of area
Symmetric Difference large Centroid Difference is also May be a displacement error
Symmetric Difference:
Non-Intersecting Area
Centroid Distance
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INTEGRATED WATER VAPOR AND PRECIPITABLE WATER
Ratios (Fcst/Obs) Area : 1.7 Median Intensity: 1.1 90th% Intensity: 1.1
Forecast: PWAT – 25.0 W/m2; Observation: IWV – 2.50 W/m2
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Strip approximately 1000 km from Coast 96h GFS IVT Forecast 24h GFS IVT Forecast GFS IVT Analysis
Jan 9, 2010 18Z
• Helps with diagnosing model performance of landfall events
• Useful for qualitative analysis
• Fits with hi-res, smaller scale domains like LAPS. IVT = Wind850mb * IWV [cm m/s]
Slide provided by W. Clark and E. Tollerud
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Centroid Difference Longitudinal and Latitudinal Bias?
Direct use of currently available attributes must be done carefully in this domain due to object truncation. • Centroid Difference
provides Qualitative lead/lag information
• Development of special attributes would benefit Quantitative spatial error analysis
• Area attributes (not shown) should be interpreted with truncation in mind
West
East
North South
Slide provided by W. Clark and E. Tollerud
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MODE USED ON NON-CLOUDY AREAS
Clear Sky
Clouds
Cloud forecast objects would have taken up most of domain so non-cloudy areas were identified
Slide provided by M. Mittermaier, 2012
MET package used
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APPLICATIONS - NOT SHOWN HERE Derived Wind Fields (divergence and convergence) A-Train downward looking radar data (X-Z plane) Time Domain (2 dimensional field and Time) Pressure fields including those for Tropical Cyclones
Operational evaluation of precipitation fields by: US NOAA Weather Prediction Center (WPC) and Saudi Arabia Presidential Ministry of the Environment (PME) (experimental)
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ENSEMBLE MODE
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APPLYING SPATIAL METHODS TO ENSEMBLES
As probabilities: Areas do not have “shape” of precipitation areas; may “spread” the area
As mean:
Area is not equivalent to any of the underlying ensemble members
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TREATMENT OF SPATIAL ENSEMBLE FORECASTS
Alternative: Consider
ensembles of “attributes”
Evaluate distributions of “attribute” errors
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EXAMPLE MAY 11, 2013
Ensemble Mean
Matched Forecast Object
Matched Forecast Object
Matched Observed Object
Unmatched Observed Object
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SPREAD INCREASES WITH TIME
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INDIVIDUAL MATCHED OBSERVED OBJECTS
1
2
3
4
5
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median
Mat
ched
For
ecas
t Are
a (g
rid s
quar
es)
Object Areas
Fcst
Obs
2 5 3 1 4
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Mat
ched
For
ecas
t Are
a (g
rid s
quar
es)
May 2013: 25 Days of Matched Observed/Forecast Pairs FORECAST AREA
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Matched Forecast Centroid Distance (grid squares) Matched Forecast Symmetric Difference (grid squares)
May 2013: 25 Days of Matched Observed/Forecast Pairs
Symmetric Difference:
Non-Intersecting Area
Centroid Distance
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ENSEMBLE MEAN MEMBERSHIP How many members typically make up ensemble mean that is matched?
3 or more
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USING MODE ON PROBABILITY FIELDS
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QPE_06 >12.7 MM VS. 50% PROB(APCP_06>12.7 MM)
Good Forecast with Displacement Error?
Traditional Metrics
Brier: 0.07 Area Under ROC: 0.62
Spatial Metrics
Centroid Distance: Obj1) 200 km Obj2) 88km
Area Ratio: Obj1) 0.69 Obj2) 0.65
1
2 Median Of Max Interest: 0.77
Obj PODY: 0.72 Obj FAR: 0.32
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MODE FOR DIFFERENT PROBABILITIES – MAY 11, 2013
Prob>2.54 mm >25%
Prob>2.54 mm >75%
Prob>2.54 mm >50%
Observation Forecast
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SUMMARY • MODE can be used for many applications, including situations
when Forecast Field and Observation field are scaled differently
• Matched pair attributes may be used synergistically to diagnose areas for model development focus and trouble-shooting
• Next steps for Ensemble Distribution Verification • Plot as distribution of attribute errors • Develop score using individual member attributes
• Next steps for Probability Verification • Modify definition of weighting and interest maps based on area-ratio to
better compare probability fields
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THANK YOU EXAMPLE MODE CONFIGURATION FILES
http://www.dtcenter.org/hwt/2010
http://www.dtcenter.org/hmt/2010 http://www.dtcenter.org/hmt/2011
MET: http://www.dtcenter.org/met/users
MET HELP: [email protected]
Email: [email protected]
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MODE TIME DOMAIN
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APPLICATION 1: VISUALIZATION/VERIFICATION OF SIMULATED ROTATING STORM TRACK LENGTHS • Time-domain object code is applied to hourly-max updraft helicity (UH) to identify
number, length, and intensity of time-domain UH objects (i.e. rotating storm tracks).
• A study was done on whether total UH path lengths could be used as a proxy for total tornado path lengths (Clark et al. 2012).
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EXAMPLE UH FORECAST PRODUCT: 27 APRIL 2011
- Max UH from any ensemble member – blue: high-based, red shading for surface-based UH.
- Thick red line – 27 April exceedence probabilities for total tornado path lengths up to 5000 km.
- Thin red – exceedence probs for all other days
- Green line – climo - Grey vertical lines mark
path lengths corresponding to 1, 2, and 10 year return periods - Length of
entire row is the total UH path length for an ensemble member; members are ordered longest to shortest.
- Lengths of segments correspond to path lengths of individual UH objects. Shading level shows max intensity of UH within each object. Red shading is for surface based and green for elevated UH tracks.