Page 1© Crown copyright 2004 A new approach to nowcasting at the Met Office Brian Golding Head of Forecasting Research Met Office 8 th September 2005.

© Crown copyright 2004 Acknowledgements  Clive Pierce  Stephen Moseley  Humphrey Lean  Nigel Roberts  Malcolm Kitchen  Roger Saunders  Peter Clark  Roderick Smith  Bob Moore  Vicky Bell  & many others

© Crown copyright 2004 Scales of Motion & Predictability Hail shaft Thunderstorm Front Extratropical Cyclone Space Scale Lifetime Predictability Nowcast 10mins1 hr12hrs3 days 30mins3 hrs36hrs9 days 5mins30min 6hrs36hrs 1000km 100km 10km 1km MCS* * Mesoscale Convective System

© Crown copyright 2004 Nimrod  Nimrod implemented 1996  6 hour nowcasts of:  Precipitation rate, accumulation & type  Lightning  Visibility, low cloud, temperature & humidity  Wind & pressure  Based on  Fusion of observation sources including radar & satellite  Extrapolation of analysis  Merged with mesoscale NWP output  5/15km grid – now 2km for precipitation  Hourly output - now 5mins for precipitation  Updated hourly - now 15 mins for precipitation

© Crown copyright 2004 Basis for using convective scale NWP InformationContent Forecast Length LogScale Log Scale (days) 0.010.11 10 Nowcast (Extrapolation Forecast) Limit (“Perfect Forecast”) NWP (Model Forecast) Hi Res NWP

© Crown copyright 2004 Improved observational & NWP forecast data  Radar: Radarnet IV, implemented summer 2005  Satellite: Autosat IV, Meteosat 8, implemented summer 2004  Convective Scale NWP, implemented 2005

© Crown copyright 2004 Improved radar processing  Centralised processing system  Processing in polar coordinates  Vertical profile correction for bright band, beam filling, attenuation & range  Clutter/anaprop removal using advanced signal processing & complementary data sources (satellite, lightning, surface)  Main benefit –  improved infilling in areas of clutter contamination

© Crown copyright 2004 Meteosat-8 Cloud Processing  Cloud mask - combination of single channel threshold tests:  Meteosat-7: Vis, IR  Meteosat-8: Vis0.6, Vis 0.8, IR3.9, IR8.7, IR10.8, IR12.0  Cloud top height -  Meteosat-7: match of satellite BT to NWP forecast temperature allowing for boundary layer stability. (IR only)  Meteosat-8: variational fit of satellite BTs to NWP forecast BTs allowing for boundary layer stability (IR6.2, IR7.3, IR8.7, IR10.8, IR12.0, IR13.4 )  Main benefit –  Low cloud detection at night, especially for use in fog nowcasting and spurious radar echo removal

© Crown copyright 2004 Convective Scale NWP  3-hourly 4km UK NWP system, available within 1 hour of data time, implemented 2005  On-demand 1km sub-area model on trial  Hourly 1km UK NWP system, available within 1 hour of data time, planned for implementation by 2010

© Crown copyright 2004 Future: Nowcasts from post-processed NWP  Integral part of NWP suite – all model output processed – minimise changes, consistent with benefit.  Products transparent to different models at different lead times ( initially T+36 with Rapid Update to T+6 but will be extended to T+144 or longer )  Regrid and downscale to 2km:  Model currently on 4km grid, but only resolves >~20km scales & orography  Rapid Update Cycle to adjust key variables to latest observations  Hourly (15min for precipitation), regardless of model update frequency  Update precipitation to Radar analysis every 15 minutes  Update visibility, cloud (& T, RH) to satellite/surface observations every hour  Update wind/pressure to surface observations every hour  Adjust early part of each forecast towards extrapolated analysis  Integrate uncertainty estimates for all variables  Diagnose required products from updated variables

© Crown copyright 2004 UK NWP model & post-processing domains New 4km grid, ~20km resolution, UK NWP model, implemented 2005 Products downscaled to 2km grid & topography on standard projection and domain

© Crown copyright 2004  Generate analysis using radar where it has good visibility, and elsewhere using variational blending of:  Meteosat visible and infrared imagery calibrated against radar  Lightning fixes (minimum rain rate)  A very short period forecast  Surface in situ weather reports  Generate adjusted NWP forecast using STEPS:  Compute advection field using optic flow algorithm,  Decompose analysis into scale cascade,  Merge model, advected analysis, autocorrelated noise, orographic enhancement,  Recompose forecast. Rapid Update : Precipitation Rate

© Crown copyright 2004 Rapid Update: Cloud Satellite images define highest cloud layer Model forecast & surface visual cloud type observations define intermediate cloud layers Surface visual & instrumental observations define lower cloud layers 29 horizontal levels, focussed near ground Analysis uses METEOSAT imagery & surface observations with forecast 1 st guess Precipitating cloud moved with precipitation vectors Non-precipitating cloud moved with model layer wind Merged with model cloud forecast

© Crown copyright 2004 Rapid Update: Visibility x x x x x x x x x Satellite area of fog/low cloud Observations  2km grid; liquid water temperature and total water variables  analysis based on METEOSAT-8 imagery and surface observations  extrapolation forecast is persistence  merged with mesoscale model forecast  hill fog added from cloud forecast

© Crown copyright 2004 Uncertainty estimates  Precipitation – STEPS noise cascade  Fog – humidity pdf  Snow – land height / fractional melting  Lightning – flash rate expressed as return period  Severe weather – Bayesian predictor combination  NWP positional uncertainty  Short Range EPS  ECMWF EPS Presenting NWP positional forecast uncertainty for Boscastle flash flood (a) exceedance probability (b) probable maximum for warning areas

© Crown copyright 2004 Diagnostic outputs  Precipitation type  Snow & hail probability, freezing rain & drizzle  Severe Weather indicators  Large hail, frequent lightning & tornadoes  Road State  MOSES-PDM-RFM  Soil moisture, run-off & river flow  Fire risk  Structural icing risk  Strong wind risk to power transmission  Distinguish normal impact risk from probability of extreme impact beyond normal planned responses.

© Crown copyright 2004 Summary  Expect 1km grid NWP to be operational by 2010  Improved NWP resolution restricts value of extrapolation to shorter lead times  Extrapolation is one of many techniques for enhancing the value of NWP output  Incorporate nowcasting in NWP post-processing:  downscaling to standard grid  frequent rapid update to latest radar/satellite/in situ observations  incorporation of uncertainty  diagnosis of impacts.

Page 1© Crown copyright 2004 A new approach to nowcasting at the Met Office Brian Golding Head of Forecasting Research Met Office 8 th September 2005.

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Page 1© Crown copyright 2004 A new approach to nowcasting at the Met Office Brian Golding Head of Forecasting Research Met Office 8 th September 2005.

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