Numerical Weather Prediction and EPS Products Severe Weather

Numerical Weather Prediction and EPS Products: Severe Weather and Quantitative Precipitation Forecasts Hamza Kabelwa Contributions from Richard H. Grumm

Motivation and overview A good forecasts is of little meaning If it does not allow for a good decision NWP and Ensembles aid in assigning confidence to a forecast Forecasting severe weather is key role Including convection, flooding and flash flooding Click to edit Master subtitle style How to effectively accomplish this Flooding requires good QPF Tools to predict high impact weather and assign confidence is our focus

The intial elements of a good Forecast Click to edit Master subtitle style

Severe Weather Ingredients associated with severe weather Critical and favorable large scale pattern Critical parameters • Instability (CAPE, helicity, stability indices) • Precipitable water moisture is critical • Lift Click to edit Master subtitle style – Terrain, density currents, and larger scale features • Models – Omega show ascent – QPF may show or imply convection

Quantitative Precipitation Forecasting (QPF) High confidence a low uncertainty Need good QPF Best QPF is likely a probabilistic QPF • Based on key thresholds which relate to flood potential Best potential for QPF in high probability areas Click to edit Master subtitle style Convection will limit predictability at times. Best QPF during floods require known Patterns and Probabilities Can refine high end amounts with higher resolution models

Precipitation Probabilities 10 mm in 24 hours Click to edit Master subtitle style

Why the focus? Instability, convergence, model ascent Click to edit Master subtitle style

Mesoscale model QPF Click to edit Master subtitle style

Ensemble Spaghetti 50 mm Click to edit Master subtitle style

Salient points Use known meteorological reasoning Know the favorable patterns Instability where expect region of convection Gain confidence in pattern, instability, and forcing Tie in ensemble data Click to edit outcomes Master subtitle stylegain confidence High probability and Better region and better confidence of event This case locally heavy rainfall • But in this case not record rainfall. • Anomalies can help with the pattern and with high end events

Raw GEFS Po. Ps and spaghetti Click to edit Master subtitle style

What Ensemble Add Patterns and probabilities Confidence in the pattern – To include high values of PW; other parameters we forecast with – Implies knowledge of patterns of high impact weather – Standardized anomalies add value too. Probabilities – Outcomes we can assign a number too. Click to edit Master subtitle style – Highlight areas of concern and interest Forecasters – Need to tie in confidence with the pattern and probabilities from the EPS

Severe weather forecast summary Know the pattern(s) associated with severe weather Determine if the pattern is present Determine instability and shear Click to edit Master subtitle style High probability Of instability such has high CAPE/TTI/KI Of precipitation in the region Of the pattern you expect with severe weather

Satellite evolution of the example Click to edit Master subtitle style

Rainfall estimates http: //www. cpc. ncep. noaa. gov/products/fews/global/CMORPH/cmorph_dly_africa_east. png Click to edit Master subtitle style

QPF forecasting We reversed and improved the severe weather version Use EFS to determine a high probability Of instability associated with convective rainfall? Of heavy rainfall in the region based ensembles? Of a pattern conducive for heavy rainfall? • Assumes you know the patterns Check Click thetopattern parameters edit Masterand subtitle style In single models and high resolution models You are already confident of the large scale Check instability and shear In high resolution models compare to EFS

End-to-end forecast-QPF Flood Example Area of high probability for high QPF Area or region you will likely predict Temper or adjust with high resolution model Think of high end amounts as a probability Impacts (A good forecast is useless if it cannot aid in making a good decision!) Click to edit Master subtitle style You need to know the antecedent conditions • Is the ground saturated or dry? • Are flows in rivers already high? • Antecedent conditions can be as important as the forecast. Ensure good forecast aids in good decisions

Revised Forecast Concept Click to edit Master subtitle style

Review A good forecasts is of little meaning If it does not allow for a good decision NWP and Ensembles aid in assigning confidence to a forecast Forecasting severe weather is key role Including convection, flooding and flash flooding Click to edit Master subtitle style How to effectively accomplish this Tools to predict high impact weather and assign confidence is our focus

Test Drive Site for Products • Try main entry point • http: //www. cpc. ncep. n oaa. gov/products/afric • Examine text products an_desk/cpc_intl/ bulletin • http: //www. cpc. ncep. n Click to edit Master subtitle style oaa. gov/products/afric • Examine use of maps an_desk/cpc_intl/afric and data+a/africa. shtml

Links • International Jump off point: – http: //www. cpc. ncep. noaa. gov/products/africa n_desk/cpc_intl/ • Main Forecast entry point – http: //www. cpc. ncep. noaa. gov/products/africa Click to edit Master subtitle style n_desk/cpc_intl/africa. shtml • East Africa tools: – http: //www. cpc. ncep. noaa. gov/products/africa n_desk/cpc_intl/eafrica. shtml