Water-Vapor Analysis Uncertaintyand Implications for Storm-ScaleRadar-Data Assimilation

David Dowell and Curtis AlexanderNOAA ESRL GSD AMB, Boulder, CO

Acknowledgments:Ming Hu, Steve Weygandt, Tanya Smirnova, Stan Benjamin, John Brown, Eric James, Patrick Hofmann,Jian Zhang

Hourly Updated NOAA NWP Models13km Rapid Refresh (mesoscale)13km RUC (mesoscale)3km HRRR (storm-scale)RUC current oper Model, new 18h fcst every hour

High-Resolution Rapid Refresh Experimental 3km nest inside RR, new 15-h fcst every hour Rapid Refresh (RR) replaces RUC at NCEP in 2011 WRF, GSI with RUC features

NOAA/ESRL/GSD/AMB Models

ModelVersionAssimilationRadar DFIRadiationMicrophysicsCum ParamPBLLSMRUCN/ARUC-3DVARYesRRTM/DudhiaThompsonGrell-DevenyiBurk-ThompsonRUCRRWRF-ARW v3.2+GSI-3DVARYesRRTM/GoddardThompsonG3 + ShallowMYJRUCHRRRWRF-ARWv3.2+None: RR I.C.NoRRTM/GoddardThompsonNoneMYJRUC

ModelRun at:DomainGrid PointsGrid SpacingVertical LevelsVertical CoordinateBoundary ConditionsInitializedRUCGSD, NCOCONUS451 x 33713 km50Sigma/ IsentropicNAMHourly (cycled)RRGSD,EMCNorth America758 x 56713 km50SigmaGFSHourly (cycled)HRRRGSDCONUS1799 x 10593 km50SigmaRRHourly (no-cycle)

HRRR Reflectivity VerificationEastern US, Reflectivity > 25 dBZ11-20 August 2011

Reflectivity DA in RR/RUC increases HRRR forecast skillHRRR bias depends strongly on parent modelCSI 40 kmRUC->HRRR RadarRR->HRRR Radar

RR->HRRR No RadarRUC->HRRR No RadarRR->HRRR RadarRR->HRRR No RadarRUC->HRRR RadarRUC->HRRR No RadarBIAS 03 kmOptimal

NOAA/ESRL/GSD/AMB Models

ModelVersionAssimilationRadar DFIRadiationMicrophysicsCum ParamPBLLSMRUCN/ARUC-3DVARYesRRTM/DudhiaThompsonGrell-DevenyiBurk-ThompsonRUCRRWRF-ARW v3.2+GSI-3DVARYesRRTM/GoddardThompsonG3 + ShallowMYJRUCHRRRWRF-ARWv3.2+YesMultiple Radar DA ExperimentsRRTM/GoddardThompsonNoneMYJRUC

ModelRun at:DomainGrid PointsGrid SpacingVertical LevelsVertical CoordinateBoundary ConditionsInitializedRUCGSD, NCOCONUS451 x 33713 km50Sigma/ IsentropicNAMHourly (cycled)RRGSD,EMCNorth America758 x 56713 km50SigmaGFSHourly (cycled)HRRRGSDCONUS1799 x 10593 km50SigmaRRHourly (no-cycle)

Composite Reflectivity 2100 UTC 11 May 2011

Composite Reflectivity 0200 UTC 11 May 2011

Composite Reflectivity 0200 UTC 11 May 2011

Impressions from Reflectivity DataAssimilation on HRRR (x=3 km) GridForecast skill from radar DAImprovement in 00-03 hr forecastsLittle change in 06-12 hr forecasts meso-/synoptic-scale forcing quickly dominates forecast?

Model inability to sustain some observed stormsConvective-scale model error and/or storm-environment analysis error?

Spurious convective stormsPervasive problemUnclear solution on convective scale

Back to the MesoscaleRapid Refresh (RR) and Rapid Update Cycle (RUC)Similarities: resolution (Dx=13 km), 3DVar DA, hourly cyclingDifferences: resulting HRRR forecasts

How different are the RR and RUC mesoscale analyses?Two realizations of a mesoscale analysisDifferences representative of analysis uncertainty?

RR->HRRR No RadarBIAS 03 kmOptimalRUC->HRRR No Radar

RR and RUC Temperature BiasCONUSAll 00/12 UTC Raobs08 July 08 Sept 2011

Very small temperature bias in both RR and RUCRRRUCRR - RUC00 hr (analysis)12 hr fcstsRRRUCRR - RUC

RR and RUC Humidity BiasCONUSAll 00/12 UTC Raobs08 July 08 Sept 2011

RUC/RR drier/moister below 650 mb, opposite aboveRR a closer fit to the observations by 6 hrs in lower tropWater vapor is the dominant source of the RH biasRRRUCRR - RUC00 hr (analysis)06 hr fcstsRRRUCRR - RUC

RR and RUC Humidity BiasCONUSAll 00/12 UTC Raobs11-22 August 2011NO RADAR DA

Without radar DA, model bias even more pronouncedRRRUCRR - RUC00 hr (analysis)06 hr fcstsRRRUCRR - RUC

HRRR Water Vapor HistogramsCONUS11-22 August 2011NO RADAR DA0 hr forecasts

RUC->HRRRhigherSurface~800 mbDifferences large enough to affect convective forecasts RR->HRRRhigherRUC->HRRRhigherRR->HRRRhigher

HRRR Reflectivity VerificationEastern US, Reflectivity > 25 dBZ11-20 August 2011NO RADAR DA04 hr fcsts

RR->HRRRRUC->HRRRRR->HRRR RUC->HRRRBIAS 03 kmOptimalRR->HRRRRUC->HRRRRR->HRRR RUC->HRRRCSI 40 kmSame SkillNo difference

HRRR Reflectivity VerificationEastern US, Reflectivity > 25 dBZ11-20 August 2011NO RADAR DA04 hr fcsts

RR->HRRRRUC->HRRRRR->HRRR RUC->HRRRBIAS 03 kmOptimalRR->HRRRRUC->HRRRRR->HRRR RUC->HRRRCSI 40 kmSame SkillNo difference

Composite Reflectivity 0800 UTC 13 Aug 2011obs2-h fcst RUC->HRRR2-h fcst RR->HRRRstorm coverage somewhat underforecast (overforecast) inRUC->HRRR(RR->HRRR)

Water VaporAnalyses8 m AGL 0600 UTC 13 Aug 2011RUC->HRRRRR->HRRRRR RUCdifferencestorm coverage somewhat underforecast (overforecast) inRUC->HRRR(RR->HRRR)

Water VaporAnalyses2600 m AGL 0600 UTC 13 Aug 2011RUC->HRRRRR->HRRRRR RUCdifferencestorm coverage somewhat underforecast (overforecast) inRUC->HRRR(RR->HRRR)

AnalysisVerticalProfiles 0600 UTC 13 Aug 2011RUC->HRRRRR->HRRRRR->HRRR

Composite Reflectivity 1500 UTC 14 Aug 2011obs3-h fcst RUC->HRRR3-h fcst RR->HRRRspurious convectionin RR->HRRR

Water VaporAnalyses8 m AGL 1200 UTC 14 Aug 2011RUC->HRRRRR->HRRRlocation ofspurious convectionin RR->HRRRRR RUCdifference

Water VaporAnalyses600 m AGL 1200 UTC 14 Aug 2011RUC->HRRRRR->HRRRdifferencesas much as10 g/kg !RR RUCdifference

AnalysisVerticalProfiles 1200 UTC 14 Aug 2011RUC->HRRRRR->HRRRRR->HRRRObservedProfile

Water-Vapor AnalysisSmall analysis differences near surfaceAbundance of surface observations

Large analysis differences (several g/kg) at low levels above surfaceMuch larger than what is considered important for convective-storm formation and evolution

Limited potential of storm-scale radar DA in the presence of large water-vapor analysis and forecast errorsSpurious convective stormsModel inability to sustain some observed storms

Reducing analysis uncertainty and biasRadar and/or satellite data?DA methods? => 3DVar cloud analysis; flow-dependent b. e. c.Model improvements? => PBL scheme

*