Performance of 4D‐Var NWP‐based nowcasting of precipitation at the Met Office for summer 2012

The Met Office developed and demonstrated an hourly cycling 1.5 km resolution NWP-based nowcast system (0–6 hour forecasts) using 4-dimensional variational data assimilation (4D-Var). This was known as the Nowcasting Demonstration Project (NDP), and was principally for prediction of convective storms for flood forecasting. The NDP was run in real-time from March 2012 to April 2013 to cover the period of the London Olympics 2012. The system was run on a domain covering southern England and Wales nested in the UK variable resolution model (UKV). The UKV used a UK-wide 1.5 km domain with 3-hourly cycling 3-dimensional variational data assimilation (3D-Var) and produced 36 hour forecasts every 6 hours. The NDP 4D-Var included standard observations, Doppler radar radial winds, humidity derived from a 3D cloud cover analysis and geostationary satellite upper-tropospheric water vapour radiances not contaminated by cloud. This was used in combination with latent heat nudging of radar-derived precipitation rates. Example case studies compare the NDP precipitation forecasts to both the operational extrapolation/merged nowcast system and the UKV forecasts. Objective comparison of fraction skill score for the period June to August 2012 shows that the NDP skill was greater than the latest UKV forecasts, available to forecasters at the same time as the NDP, for the whole 6 hour forecast period. The skill of the NDP was greater than the operational extrapolation/merged nowcast beyond T+2 hours.

[1]  I. Zawadzki,et al.  Scale-Dependence of the Predictability of Precipitation from Continental Radar Images. Part I: Description of the Methodology , 2002 .

[2]  V. Masson,et al.  The AROME-France Convective-Scale Operational Model , 2011 .

[3]  P. Courtier,et al.  A strategy for operational implementation of 4D‐Var, using an incremental approach , 1994 .

[4]  David Simonin,et al.  Doppler radar radial wind assimilation using an hourly cycling 3D‐Var with a 1.5 km resolution version of the Met Office Unified Model for nowcasting , 2014 .

[5]  S. P. Ballard,et al.  Efficient moist physics schemes for data assimilation. I: Large‐scale clouds and condensation , 2009 .

[6]  Lawrence L. Takacs,et al.  Data Assimilation Using Incremental Analysis Updates , 1996 .

[7]  Juanzhen Sun,et al.  Radar Data Assimilation with WRF 4D-Var. Part I: System Development and Preliminary Testing , 2013 .

[8]  Claude Lemaréchal,et al.  Some numerical experiments with variable-storage quasi-Newton algorithms , 1989, Math. Program..

[9]  M. Dixon,et al.  TITAN: Thunderstorm Identification, Tracking, Analysis, and Nowcasting—A Radar-based Methodology , 1993 .

[10]  Chris G. Collier,et al.  GANDOLF: a system for generating automated nowcasts of convective precipitation , 2000 .

[11]  A. Staniforth,et al.  A new dynamical core for the Met Office's global and regional modelling of the atmosphere , 2005 .

[12]  A. Slingo,et al.  Studies with a flexible new radiation code. I: Choosing a configuration for a large-scale model , 1996 .

[13]  Nigel Roberts,et al.  Characteristics of high-resolution versions of the Met Office unified model for forecasting convection over the United Kingdom , 2008 .

[14]  Elizabeth E. Ebert,et al.  Sydney 2000 Forecast Demonstration Project: Convective Storm Nowcasting , 2004 .

[15]  Neill E. Bowler,et al.  Use of a stochastic precipitation nowcast scheme for fluvial flood forecasting and warning , 2005 .

[16]  Peter N. Francis,et al.  Variational assimilation of cloud fraction in the operational Met Office Unified Model , 2011 .

[17]  Peter Clark,et al.  Prediction of visibility and aerosol within the operational Met Office Unified Model. I: Model formulation and variational assimilation , 2008 .

[18]  N. B. Ingleby,et al.  Improved variational analyses using a nonlinear humidity control variable , 2013 .

[19]  Keith A. Browning,et al.  Review Lecture: Local weather forecasting , 1980, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[20]  René Laprise,et al.  Predictability of Precipitation Patterns: An Operational Approach , 1994 .

[21]  Marion Mittermaier,et al.  Improving short‐range high‐resolution model precipitation forecast skill using time‐lagged ensembles , 2007 .

[22]  Nigel Roberts,et al.  Impact of Data Assimilation on Forecasting Convection over the United Kingdom Using a High-Resolution Version of the Met Office Unified Model , 2009 .

[23]  T. Davies.  Lateral boundary conditions for limited area models , 2014 .

[24]  N. Roberts,et al.  Scale-Selective Verification of Rainfall Accumulations from High-Resolution Forecasts of Convective Events , 2008 .

[25]  Chris G. Collier,et al.  On the performance of a conceptual model of convection during preparations for the world weather research project nowcasting intercomparison during the olympic games in Sydney, Australia , 2000 .

[26]  Nancy Nichols,et al.  Breakdown of hydrostatic balance at convective scales in the forecast errors in the Met Office Unified Model , 2012 .

[27]  Damian R. Wilson,et al.  A microphysically based precipitation scheme for the UK meteorological office unified model , 1999 .

[28]  John Derber,et al.  The National Meteorological Center's spectral-statistical interpolation analysis system , 1992 .

[29]  Gérald Desroziers,et al.  Background‐error covariances for a convective‐scale data‐assimilation system: AROME–France 3D‐Var , 2011 .

[30]  Olivier Caumont,et al.  Operational Implementation of the 1D+3D-Var Assimilation Method of Radar Reflectivity Data in the AROME Model , 2014 .

[31]  Anthony Hollingsworth,et al.  The statistical structure of short-range forecast errors as determined from radiosonde data , 1986 .

[32]  G. Martin,et al.  A New Boundary Layer Mixing Scheme. Part I: Scheme Description and Single-Column Model Tests , 2000 .

[33]  M. J. P. Cullen,et al.  Adaptive mesh method in the Met Office variational data assimilation system , 2011 .

[34]  Rita D. Roberts,et al.  Nowcasting Challenges during the Beijing Olympics: Successes, Failures, and Implications for Future Nowcasting Systems , 2009 .

[35]  B. Macpherson,et al.  The Impact of MOPS Moisture Data in the U.K. Meteorological Office Mesoscale Data Assimilation Scheme , 1996 .

[36]  Jean-François Caron,et al.  Mismatching Perturbations at the Lateral Boundaries in Limited-Area Ensemble Forecasting: A Case Study , 2013 .

[37]  A. Seed,et al.  STEPS: A probabilistic precipitation forecasting scheme which merges an extrapolation nowcast with downscaled NWP , 2006 .

[38]  Jorge Nocedal,et al.  On the limited memory BFGS method for large scale optimization , 1989, Math. Program..

[39]  Adrian Lock,et al.  A New Boundary Layer Mixing Scheme. Part II: Tests in Climate and Mesoscale Models , 2000 .

[40]  P. J. Mason,et al.  Large‐eddy simulation of stable atmospheric boundary layers with a revised stochastic subgrid model , 1994 .

[41]  L. Berre,et al.  The representation of the analysis effect in three error simulation techniques , 2006 .

[42]  K. Browning,et al.  Quantification of the importance of wind drift to the surface distribution of orographic rain on the occasion of the extreme Cockermouth flood in Cumbria , 2013 .

[43]  A. Lorenc,et al.  The Met Office global four‐dimensional variational data assimilation scheme , 2007 .

[44]  Donald W. Burgess,et al.  The Sydney 2000 World Weather Research Programme Forecast Demonstration Project: Overview and Current Status , 2003 .

[45]  C. G. Collier,et al.  Nowcasting of precipitation systems , 1989 .

[46]  P. Bauer,et al.  Satellite cloud and precipitation assimilation at operational NWP centres , 2011 .

[47]  B. Golding.  Nimrod: a system for generating automated very short range forecasts , 1998 .

[48]  Harold E. Brooks,et al.  Verification of Nowcasts from the WWRP Sydney 2000 Forecast Demonstration Project , 2004 .

[49]  Yong-Run Guo,et al.  The Weather Research and Forecasting Model's Community Variational/Ensemble Data Assimilation System: WRFDA , 2012 .

[50]  N. B. Ingleby,et al.  The Met. Office global three‐dimensional variational data assimilation scheme , 2000 .

[51]  C. Schraff,et al.  Assimilation of radar‐derived rain rates into the convective‐scale model COSMO‐DE at DWD , 2008 .

[52]  B. Macpherson,et al.  A latent heat nudging scheme for the assimilation of precipitation data into an operational mesoscale model , 1997 .

[53]  Ken Mylne,et al.  Forecasting Capabilities for the London 2012 Olympics , 2014 .

[54]  Kazuo Saito,et al.  The Operational JMA Nonhydrostatic Mesoscale Model , 2006 .

[55]  M. J. P. Cullen,et al.  A new implementation of the adaptive mesh transform in the Met Office 3D‐Var System , 2012 .

[56]  Olivier Dupont,et al.  AROME–NWC: a new nowcasting tool based on an operational mesoscale forecasting system , 2015 .

[57]  Andrew C. Lorenc,et al.  Why does 4D‐Var beat 3D‐Var? , 2005 .

[58]  C. Donlon,et al.  The Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) system , 2012 .

[59]  Juanzhen Sun,et al.  A Frequent-Updating Analysis System Based on Radar, Surface, and Mesoscale Model Data for the Beijing 2008 Forecast Demonstration Project , 2010 .

[60]  I. Zawadzki,et al.  Predictability of Precipitation from Continental Radar Images. Part III: Operational Nowcasting Implementation (MAPLE) , 2004 .

[61]  James W. Wilson,et al.  Impacts of Forecaster Involvement on Convective Storm Initiation and Evolution Nowcasting , 2012 .

[62]  Clive Pierce,et al.  Radar products for hydrological applications in the UK , 2012 .

[63]  Juanzhen Sun,et al.  Use of NWP for Nowcasting Convective Precipitation: Recent Progress and Challenges , 2014 .

[64]  Clive Pierce,et al.  Formulation and evaluation of a scale decomposition‐based stochastic precipitation nowcast scheme , 2013 .

[65]  Y. Honda,et al.  A pre‐operational variational data assimilation system for a non‐hydrostatic model at the Japan Meteorological Agency: formulation and preliminary results , 2005 .

[66]  I. Zawadzki,et al.  Predictability of Precipitation from Continental Radar Images. Part IV: Limits to Prediction. , 2006 .