1. Nowcasting and Short Range NWP at the Australian Bureau of Meteorology
Peter Steinle
Earth System Modelling Group
Alan Seed
Weather & Environmental Prediction Group

2. Rainfall Nowcasting in the BoM …
Short Term Ensemble Prediction System (STEPS)
Estimation & Nowcast (radar & gauge)
Short forecast (radar, gauge & NWP)
NWP in the BoM …
Aust. Community Climate & Earth System Simulator (ACCESS)
Met Office Unified Modelling System
Bringing them together ….
Strategic Radar Enhancement Program (SREP)
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

3. Initializing the nowcast: Multi-radar QPE
Mosaic of Sydney area radars
10 min, 2 km resolution
Gauge adjusted QPE for each radar
Advect images to a common time:
1-5 min forecasts
Blend the radars:
inverse error variance as weights
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

4. STEPS QPN Spectral decomposition of a rainfall fieldkm km km km km
2-4-8 km km
We break up the rainfall map into a collection of maps where only the patterns of a small range of sizes are allowed. The centre top image is the pattern for 512 – 1024 km scales, the top right image contains only km scales and so on to the smaller scales. We make a nowcast for each of the scales and then add the scales together to get the rainfall forecast. We replace the observed pattern with a statistical pattern during the forecast period, the large scales evolve slowly and the small scales are made to evolve quickly, like rainfall.
Use Fourier notch filters to isolate narrow bands of wavelengths in the field
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

5. Short Term Ensemble Prediction System STEPS QPN: 0 – 90 minutes
Estimate the advection field using rainfall fields
Decompose the rainfall field into components
Estimate the LaGrange auto-correlation for each component
Generate 30-member ensemble every 6 minutes
Perturb the radar analysis with a radar estimation error model
Perturb the advection field
Generate the deterministic nowcasts based on the perturbed radar data and advection field
Generate a series of synthetic rainfall (noise) using the multiplicative cascade statistical model and parameters that have been estimated from the current rain field
Add the noise to the deterministic nowcasts; the weight of the noise is calculated using the skill of the nowcast for that lead time and spatial scale
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

6. STEPS QPN 60 minute rainfall accumulation forecasts
Forecast – ensemble mean
Radar accumulation
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

7. STEPS QPN 60 minute probability products
Probability accumulation > 10 mm
Probability accumulation > 20 mm
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

8. STEPS QPF: 0 – 6 hours
Probability of rain > 1 mm for 2 & 3 hour lead times, Melbourne
Rainfall intensity forecast,
150 min lead time, Sydney
Melbourne, Sydney, Brisbane – 500 km domain, 2 km & 10 min resolution
Blends radar forecasts with Numerical Weather Prediction
30 member ensemble updated every hour
10-min forecasts of rainfall intensity out to 6 hours
Probability products for hourly accumulations for next 6 hours
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

9. STEPS QPF 0 – 6 hour with NWP blending
Skill of nowcast is a function of scale and lead time
Skill of NWP is a function of scale
Decompose the NWP into components
Blend the NWP and nowcast components, weights a function of lead time and scale
Generate the ensemble by adding statistical noise that represents the error in the deterministic blended forecast for each component
Combine the components into the forecasts
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

10. STEPS QPF Weights for nowcast & NWP
Blending
Weights for components for scales centred on 125km. Weights chosen to presevve VARIANCE
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

11. NWP systems Met Office Unified Model (UM7.5,L70) 4km City Systems
6 hourly 4dVAR : Global, Region & TC
4km City Systems
No Assimilation (3dVAR expt.)
1.5km UM7.6/L70 (Experimental)
3dVAR
+ radar winds & precip(LHN)
Relocatable
Ensembles
Global & Regional EPS in research
Need deterministic high res.
Global: N320 (~40km) + 4dVAR
Regional 0.11o +4dVAR
City: 4km ; no DA
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

12. SREP to deliver:
4 new radars delivering QPE & F products as appropriate for radar location
STEPS blending radar nowcasts with NWP in the Capital Cities
NWP assimilating radar data operationally
Start with Latent Heat Nudging for simplicity & baseline
Begin moving to VAR soon
Rapid update cycle and relocatable domains tested and made ready for transition into operations
Prototype radar QC system ready for transition into operations
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

13. Extensive testing on Brisbane Jan2-14 2011
Hourly precipitation
Radar+Gauge
Analysis
SREP 1.5km
6hr forecast
Operational 0.05o
6hr forecast
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

14. Have STEPS & NWP…So all done & dusted???
Apart from one or two problems…
Rainfall estimation
Systematic errors from clutter and quality control
Model calibration
Overdoes heavy precipitation in tropics
Assimilation
Large initial rainfall in the tropics
Dirty laundry time…..
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

15. QPE Errors Climatology – truth from rain gauges
Melbourne
Mean daily rain rate
Gauge data only
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

16. QPE Errors Climatology – radar
Systematic errors are
obvious in long
accumulations
Blocking from hills
Clutter
Radar clutter rejection
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

17. Area & Volume vs Rainfall Rate (2-11 Jan)
Obs
3dVAR+LHN
3dVAR only
1.5km – too much convection & too strong
4,5 & 6 hour forecasts
Model calibration
Latent Heat Nudging needs calibration
One of the worse events
Sydney events looked much better
0.05o & 0.11o problems with heavy precipitation too
3,4,5,….,14 hour forecasts
Little sensitivity to forecast length
3dVAR / no 3dVAR similar
Obs
3dVAR+LHN
0.05o (FC only)
0.11o 4dVAR
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

18. After effects from Latent Heat Nudging …
Hourly precipitation
Radar+Gauge
Analysis
SREP 1.5km
4hr forecast
Operational 12km
4hr forecast
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology

19. Summary Rainfall nowcasting established NWP “developing”
In the queue for operations
Improved radar quality control being tested
NWP “developing”
Seems better much behaved away from tropics
More extensive trials in Sydney underway
Tropical NWP still a challenge
Restrain LHN
Systems are in place
Analysis → Nowcast → NWP blend → NWP
Calibration/tuning of components ongoing
The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology