nowcasting convection
DESCRIPTION
Nowcasting Convection. Fusing 0-6 hour observation- and model-based probability forecasts. Collaborators: Cindy Mueller, Steve Weygandt, Jim Wilson, David Ahijevych, Dan Megenhardt. WWRP Symposium on Nowcasting and Very Short Range Forecasting Toulouse, France, 7 September 2005. - PowerPoint PPT PresentationTRANSCRIPT
Nowcasting ConvectionNowcasting Convection
Fusing 0-6 hour observation- and model-based probability forecasts
WWRP Symposium on Nowcasting and Very Short Range ForecastingToulouse, France, 7 September 2005
Collaborators: Cindy Mueller, Steve Weygandt, Jim Wilson, David Ahijevych,Dan Megenhardt
0 1 2 3 4 5 6 Forecast Length, hours
.2
.4
.6
.8
1.0
Accuracy of Rainfall Nowcasts>1 mm/h
GRID MESH 20 km Jun-Oct 2002
Courtesy of Shingo Yamada JMA
ExtrapolationP
ersistence
NWP
CS
I
Gap in Forecast Skill
Others have also quantified this in various ways (e.g., Golding 2000, and many others at this conference.
I) Probabilistic Forecasting
-> National Convective Weather Forecast (NCWF) – obs-based
-> RUC Convective Probability Forecast (RCPF) – model-based
II) Methodology
III) Results/Verification
IV) Future Work
Outline
just saw Weygandt talk!
See Mueller et al. poster 5.21!
– 0-2 hr probability forecasts
– Includes extrapolation, growth and dissipation
– Available on Experimental ADDS (http://weather.aero/convection)
Operational NCWF
Probabilistic Forecasts Systems
Probabilities based on:
– Spatial coverage of convective precip predicted by the RUC-20 model
– Square filter of 180 km
– Precipitation rate threshold for convection (1-2 mm/hr)
Probabilities based on:– Spatial coverage of MergedGrowth (MG)– Elliptical filter with time-dependent size (1 hr, 2 hr, 3-6 hr : 60 km, 120 km, 180 km)– MG(VIL,ltng) thresholded for convection
P.k
1 h2 h
P
National Convective Weather Forecast RUC Convective Prob. Forecast
Summary of Strengths and Weaknesses of NCWF and RCPF
• Area-coverage– RUC : overestimates coverage and likelihoods
too high
• Initiation– RUC : good (large-scale instability and frontal)– NCWF : not handled
• Motion– RUC : improves with lead time– NCWF : degrades with lead time
• Dissipation– NCWF and RUC: similar skill
Methodology
Schematic of Methodology
NCWF
Validation
MergedProbabilistic
Product
Calibration
RCPF
Summing
WSR-88DClimatology
ClimatologicalDissipation
Coverage Maps WSR-88D
Interpolation to 4km Grid
MethodologyCalibration of RUC Probabilities using June 2005 Validation Data
OBS COV NCWF RUC . 0% 0% 0-35% 5% 5% 35%10% 10% 55%20% 20% 70%
Obs Coverage = 20%Obs Coverage = 10%
2, 4, 6 hr fcsts for each p
Obs Coverage = 5%
50%75% 60%
40%
75%
60%50%
25%
50%
40%30%
RUC Prob Levels, p
Methodology
•Remove excessive coverage values•Shrink Area Coverage without decreasing POD
Original 6hr RUC Prob Fcst
WSI @ Forecast Time
WSI - Validation
Fcst time: 2000 UTC Valid: 0200 UTC
After Scaling
Fcst time: 2000 UTC Valid: 0200 UTC
Use diurnal climo of fractional change in WSR-88D freq of convection to incorporate dissipation.
Freq40+dBZ(UTC) / F40+dBZ(UTC)
WSR-88 D climo from 6 warm seasons frequency of echo > 40 dBZ (Knievel et al. 2004)
Methodology
“…a combination of rainfall statistics containing propagation information with NWP predictions may offer significant improvement in warm rain prediction.” – Davis et al. (2003)
10
F(1)/F(0) in 6 hrs
Area Coverage > 40 dBZ
Trending dissipation using Climo
June 2005 Area Coverage Diurnal Composite
Methodology
*Note: Moving gray box indicates 6 hr period over which fractional change is calculated.
Regionally:• Diurnal Cycle in SE US• Propagation evident across Great Plains
Nationally: Convective area shrinking between 19 and 4 UTC.
Masking of RUC Probabilities using Climo
Methodology
• Apply climo trending by multiplying with RCFP • Reduces RCFP in areas/time where convection is not climatologically preferred (SE at night)
After ScalingAfter Climo MaskingOriginal 6hr RUC Prob Fcst
At Forecast Time
WSI - Validation
Fcst time: 2000 UTC Valid: 0200 UTC
•Remove excessive coverage values•Shrink Area Coverage without decreasing POD
Fcst time: 2000 UTC Valid: 0200 UTC
Case Study
1-6 hr Probability Forecasts
Extrapolation RUC Convective Probabilities
WSI @ Forecast Time
WSI - Validation
Fcst Valid Times: 1600 – 2200 UTC by 60 min
Radar Data 1400- 1600 UTC by 30 min
Fcst Valid Times: 1600 – 2200 UTC by 120 min
1-6 hr Merged Probability Forecast
WSI @ Forecast Time
WSI - Validation
WSI: 1400-1600 UTC by 30 min; Fcst: 1600 – 2200 UTC by 60 min
Statistical Evaluation
Comparing NCWF05-05, RCPF50-05, Merged05-05
Validation Region
Validation Period : 01-14 Aug 2005
Merged
NCWF
RUC
Thank You!
Methodology for Merging
• Calibrate RUC Probabilities to be comparable with NCWF values
- Validation of RCFP and NCWF from June 05 data• Mask RUC Probs. using climatological tendencies observed with National network of WSR-88Ds
-(Carbone et al. 2002, Davis et al. 2003)-Create climatological diurnal cycle of fractional
changes in the coverage of convection.
• Interpolate RCFP to NCWF 4 km grid• Add NCWF and RUC Probabilities• Apply smoothing filter
Box diagram
12 Aug 2005 Case Study
WSI National Mosaic