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

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

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

STEPS QPN Spectral decomposition of a rainfall field 128-256-512 km 64-128-256 km 32-64-128 km 16-32-64 km 8-16-32 km 2-4-8 km 4-8-16 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 256-512 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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