Status and Challenges in Nowcasting High Impact Weather Rita - PowerPoint PPT Presentation

Status and Challenges in Nowcasting High Impact Weather Rita Roberts National Center for Atmospheric Research With contributions from Jim Wilson WSN16 7/25/2016 Rita Roberts NCAR/RAL

Nowcasting Timeline WMO Forecast Kano, Nigeria, 1956 Demonstration Program Sydney 2000 Olympics Microburst Aviation Accident Herb Ligda WSR-57 Radar Detection of Colliding Sea Breezes Extrapolation of Radar Echoes 1976 1960 2000 1984 1953 1965 First U.S. weather satellite launched from Cape Canaveral, FL International Nowcasting James Purdom: Some uses of GOES imagery Demonstrations in mesoscale convection forecasting WSN16 7/25/2016 Rita Roberts NCAR/RAL

Use of satellite soundings and imagery for nowcasting and very-short-range forecasting J. F. W. Purdom A scheme for the delineation and extrapolation of thunderstorms from GOES We’ve been at this for a long time!! satellite data G. L. Austin and A. Bellon Nowcasting with Doppler radar: the forecaster-computer relationship J. Wilson and R. Carbone Short-period forecasts in West Africa using Meteosat data J. R. Milford and G. Dugdale Digital radar data as an aid in nowcasting in Hong Kong C. Y. Lam The United Kingdom Meteorological Office mesoscale forecasting system Are we making progress? B. W. Golding and N. A. Machin A one-level mesoscale model suitable for nowcasting and short-term forecasting in regions of complex terrain C. F. Mass and D. P. Dempsey FRONTIERS – Progress with a system for nowcasting rain K. M. Carpenter and K. A. Browning Interactive computer display systems in nowcasting D.A. Chisholm and A. J. Jackson Nowcasting using lightning location techniques R. E. Orville User requirements for very short range weather forecasts: Some key issues A. M. Murphy and B. B. Brown 1984 WSN16 7/25/2016 Rita Roberts NCAR/RAL

Marine Weather Tornadoes Aviation Lake Victoria fisherman What is it going to take to improve nowcasts, watches and warnings of high impact weather so that people will take action to save lives and property? Transportation Sporting Events Flash floods/ land slides Road weather WSN16 7/25/2016 Rita Roberts NCAR/RAL

OUTLINE • Status of 0-6 hour nowcasting • Challenges in nowcasting • Promising technologies and needs WSN16 7/25/2016 Rita Roberts NCAR/RAL

NOWCASTING STATUS We know the importance of convergence boundaries for convection Initiation, thunderstorms, wind shifts and heavy rain Bamako, Mali 9 June 2008 Bamako-Senou International Airport WSN16 7/25/2016 Rita Roberts NCAR/RAL

NOWCASTING STATUS Colorado, Tiwi Islands, Convergence boundaries are ubiquitous! U.S.A. Australia They play a role in : • convection initiation • surface moisture gradients • storm growth • updraft and downdraft intensities Bamako, Beijing, Mali China • storm dissipation • upscale growth of storms into MCSs Gust front Dust RGB plots of low-level convergence boundaries and storm initiation and evolution above these boundaries (Jochen Kerkmann and Daniel Rosenfeld). b) 0900 UTC c) 1800 UTC a) 0100 UTC WSN16 7/25/2016 Rita Roberts NCAR/RAL

NOWCASTING STATUS Long-lived nature of gust fronts associated with MCS convection in North-Western Africa The track of the dusty gust front, using RGB dust imagery, associated with a synoptic-scale event from 3-5 August 2006, propagating northward through West Africa. For the period from June-September 2006, the distances traveled by gust fronts ranged from 160 km – 1920 km! M. McGraw-Herdeg, M.S. Thesis, 2010 WSN16 7/25/2016 Rita Roberts NCAR/RAL

NOWCASTING STATUS Nowcasting Tools Radar echo extrapolation is still primary tool ( over 59 years) Among the most used are: TITAN, SCIT, MAPLE, TREC, Optical Flow TITAN as used in Australia Trending size and intensity Extrapolation skill not very useful drops rapidly with time Storm echo Time 1 Time 2 Time 3 North Time 4 Skill Nowcast for Time 5 Nowcast lead time East WSN16 7/25/2016 Rita Roberts NCAR/RAL

Diurnal Storm Tracks along the Colorado Rocky Mountains Storm extrapolation techniques over complex TITAN Storm tracks terrain do not take into for 01 July 2015 account the impact of terrain on storm growth and decay. During the period from 01 June – 15 Aug 2014 Colorado High Plains 91% of storms that initiated Rocky 1400 m elevation above an elevation of 2600 m Mountains dissipated before reaching 1400 m NCAR Autonowcaster system now accounts for impact of terrain on storm extrapolation WSN16 7/25/2016 Rita Roberts NCAR/RAL

NOWCASTING STATUS There have been some noteworthy nowcast successes Lead times for supercell tornadoes and severe weather warnings have increased significantly Automated wind shear Forecaster warnings warnings at airports of flash floods WSN16 7/25/2016 Rita Roberts NCAR/RAL

Aviation Ground De-icing Display Continuous measurements of the Liquid Water Equivalent (LWE) of snowfall and rainfall rates used to support decisions on when to de-ice planes… … what type of fluid to use, and how long to de-ice…. Increasing Rate Radar, snow gauge and Cross-correlation tracker is used in this system Rasmussen et al., BAMS 2001 WSN16 7/25/2016 Rita Roberts NCAR/RAL

NOWCASTING STATUS Need for Integrated Displays The message is being heard! More forecast offices are setting up integrated displays for viewing nowcast products and producing watches and warnings Met́ éo France Rapid Development Thunderstorm (RDT) display WSN16 7/25/2016 Rita Roberts NCAR/RAL

NOWCASTING STATUS Expert Systems (heuristic nowcasting tools) can add improved skill over extrapolation Example from NCAR AutoNowcaster 1hr nowcast of rainfall amount Radar Reflectivity at 08Aug2008 0711PM Reflectivity one hour before flash flood Flash Flood in Denver Where will the flood be? WSN16 7/25/2016 Rita Roberts NCAR/RAL

NOWCASTING STATUS Limitations and Increasing Capabilities in Numerical Weather Prediction for Nowcasting Real-time WRF forecast (4 km) Initialized 04 June 2005 00 UTC Composite NEXRAD Radar NWP Reflectivity forecast WSN16 7/25/2016 Rita Roberts NCAR/RAL

NOWCASTING STATUS Blending Systems Extrapolation Forecast Consolidated Storm Prediction for Aviation (CoSPA) Blended Forecast (12-20 UTC ) Blending Extrap Dash : 15 to 00 UTC Solid : 00 to 15 UTC Model Calibration + Phase Corr Courtesy of James Pinto WSN16 7/25/2016 Rita Roberts NCAR/RAL

Nowcasting Status: Assimilation of Radar Data into NWP 07 Aug 2015 3 hr rainfall Accumulation (21-24 Z) Radar Reflectivity, VDRAS winds at 21Z , at forecast time MRMS 3hr rain accumulation (21-24 Z) 3DVar with Radar Assimilation 3hr forecast of rain accum (21-24 Z) 3DVar NO Radar Assimilation 3hr forecast of rain accum (21-24 Z) WSN16 7/25/2016 Rita Roberts NCAR/RAL

NOWCASTING STATUS Current Status of NWP with Radar Data Assimilation We asked some experts….. Sue Ballard Jenny Sun Ming Xue Isztar Zawadzki Limitations 1. The spin-up cycle of NWP models limits ability to use model forecasts in the 0-2hr time period. 2. Representation of background errors. 3. Insufficient observations of wind, temperature and moisture in the non-precipitating environment. 4. Insufficient techniques for extracting multi-scale information from observations and forecast background. Increasing Capabilities 1) More frequent NWP update cycles and higher resolution models. 2) Reflectivity data assimilation is showing clear improvements in convective storm forecasts. Not so much with radial velocity assimilation. 3) Germany, France and UK operation centers are showing convective scale benefit with radar assimilation in 3D-Var, 4D-Var and nudging. 4) Most radar data assimilation systems have shown positive impact on hourly precipitation forecasts up to 6-8 hours (others say impact is only out to 4 hrs). WSN16 7/25/2016 Rita Roberts NCAR/RAL

Status in NWP Nowcasting In summary:  For larger scale precipitation systems, radar data assimilation into numerical model is improving forecasts in roughly the 3 -6 hr forecast period  However that improvement has not yet been realized for smaller scale convective events.  For example the models may tell us that western Kansas will have an MCS, but they are not able to forecast which community will have a flash flood and how intense it may be. WSN16 7/25/2016 Rita Roberts NCAR/RAL

Challenges in Nowcasting Additional barriers to improving nowcasting Must capture boundary layer convergence lines Automated convergence line detection : Automated methods have been tried for years with only modest success. The time maybe right to try again with more advanced feature detection tools and using dual-polarization radar fields. WSN16 7/25/2016 Rita Roberts NCAR/RAL

Challenges in Nowcasting using NWP and Radar Data Assimilation Prediction of Elevated Convection Initiation • 50 % of nighttime convection arises from elevated convection initiation above a stable boundary layer over the Great Plains and eastern U.S. • Elevated convection often organizes into MCSs, producing heavy precipitation and flash floods • Specific challenges in nowcasting -Location and onset of initial development To improve scientific understanding, the Plains Elevated Convection At Night (PECAN) experiment (courtesy Frederic Fabry) was conducted in June-July 2015. WSN16 7/25/2016 Rita Roberts NCAR/RAL