the 10th annual northeast regional operational workshop, albany, ny northeast regional ensemble...

The 10th annual Northeast Regional Operational Workshop, Albany, NY

Northeast Regional Ensemble Northeast Regional Ensemble Simulations of the Simulations of the

10 February 2008 Lake Effect Snow 10 February 2008 Lake Effect Snow Event:Event:

WRF Wind Biases and their Implications on WRF Wind Biases and their Implications on Forecasted Snow Band PositionForecasted Snow Band Position

Justin Arnott and Michael EvansJustin Arnott and Michael Evans

NOAA / NWS Binghamton, NYNOAA / NWS Binghamton, NY


IntroductionIntroduction Zaff and Ballentine (COMET partners Zaff and Ballentine (COMET partners

project) showed a southward bias for project) showed a southward bias for forecasted Erie/Ontario LES bands for a forecasted Erie/Ontario LES bands for a collection of 2006-2007 casescollection of 2006-2007 cases

Has this bias continued into 2007-2008? Has this bias continued into 2007-2008? If so, is this bias adversely impacting the If so, is this bias adversely impacting the

Northeast Regional Ensemble?Northeast Regional Ensemble? What causes the bias/how do we fix it?What causes the bias/how do we fix it?

Both WRF cores exhibited a southward bias. Both WRF cores exhibited a southward bias.

The The ARW’s south bias was greater than the ’s south bias was greater than the NMMARW (mean -18.7 km) NMM (mean -6.3 km).


The Northeast Regional EnsembleThe Northeast Regional Ensemble

Six 12 km WRF-EMS runsSix 12 km WRF-EMS runs

Goal: Probabilistic LES guidance that adds Goal: Probabilistic LES guidance that adds to what is provided by operational 12 km to what is provided by operational 12 km NAM (NMM)NAM (NMM)

Member WRF Core

IC/BC Physics PBL CPS

BGM ARW NAM Lin et al. YSU KF

CTP* NMM NAM Ferrier MYJ TKE BMJ

CLE ARW GFS Lin et al. YSU KF

ALB ARW NAM Lin et al. YSU KF

BTV NMM GFS Ferrier MYJ TKE BMJ

BUF NMM GFS Ferrier MYJ TKE KF

Experimental* ARW NAM Ferrier MYJ TKE BMJ


The Event – 10Feb2008The Event – 10Feb2008 Persistent deep, cold westerly flowPersistent deep, cold westerly flow

““Easy” case for modelsEasy” case for models

LAPS Sounding 0611FEB2008

RUC 850 hPa Analysis 0611FEB2008


The Event – 10Feb2008The Event – 10Feb2008


A good forecast?A good forecast?

Ensemble does a good job pointing Ensemble does a good job pointing out band locationout band location

Some question about whether band Some question about whether band sinks into Onondaga/Madison countiessinks into Onondaga/Madison counties

Do any ARW/NMM biases exist here?Do any ARW/NMM biases exist here?


----- NMM Members

----- ARW Members

The Event – 10Feb2008The Event – 10Feb2008


ARW vs. NMMARW vs. NMM

Bias is apparent – ARW further southBias is apparent – ARW further south ARW “upwind band development point” ARW “upwind band development point”

near or even on shore!near or even on shore! ARW members alone in bringing band ARW members alone in bringing band

into northern half of Onondaga/Madison into northern half of Onondaga/Madison countiescounties

Current BGM run is ARW…uh oh!Current BGM run is ARW…uh oh! Can we change the settings in this run Can we change the settings in this run

to improve its performance?to improve its performance?


Sensitivity Simulation Sensitivity Simulation

Member WRF Core

IC/BC Physics PBL CPS

BGM ARW NAM Lin et al. YSU KF

CTP* NMM NAM Ferrier MYJ TKE BMJ

CLE ARW GFS Lin et al. YSU KF

ALB ARW NAM Lin et al. YSU KF

BTV NMM GFS Ferrier MYJ TKE BMJ

BUF NMM GFS Ferrier MYJ TKE KF

Experimental* ARW NAM Ferrier MYJ TKE BMJ

mm

QPF, for the one hour ending 06Z11FEB008 (mm).


Sensitivity ResultsSensitivity Results

Sensitivity simulation shows Sensitivity simulation shows nono improvementimprovement This run was identical to CTP-NMM run except This run was identical to CTP-NMM run except

model coremodel core Numerous other sensitivity simulations showed Numerous other sensitivity simulations showed

nearly identical resultsnearly identical results

Implications for ensembleImplications for ensemble ARW members biased (this bias was seen during ARW members biased (this bias was seen during

other 2007-2008 events)other 2007-2008 events) Bias causes Bias causes unnecessary spreadunnecessary spread in the ensemble in the ensemble Usefulness of the ensemble suffersUsefulness of the ensemble suffers


Reason for BiasReason for Bias10 m wind speed, averaged through a 24 hour simulation (m/s).

m/s


The SolutionThe Solution

Still working with NMM/ARW developers on Still working with NMM/ARW developers on the reason for this low-level wind differencethe reason for this low-level wind difference Surface roughness computation changes?Surface roughness computation changes?

WRF version 3 (WRF EMS uses version WRF version 3 (WRF EMS uses version 2.1.2) was released in 2008. Can a newer 2.1.2) was released in 2008. Can a newer WRF version help?WRF version help? Let’s try an identically configured run using Let’s try an identically configured run using

version 3version 3


The Solution…for now!The Solution…for now!

mm

m/s

10 m wind speed, averaged through a 24 hour simulation (m/s).

QPF, for the one hour ending 06Z11FEB008 (mm).


The Solution…continuedThe Solution…continued

WRF ARW version 3 outperforms WRF ARW version 3 outperforms version 2 even with identical settingsversion 2 even with identical settings Smaller (although not removed) wind biasSmaller (although not removed) wind bias Smaller LES Band position errorSmaller LES Band position error

Suggestion:Suggestion: If using ARW, consider version 3 for 2008-If using ARW, consider version 3 for 2008-

2009 LES season2009 LES season


ConclusionsConclusions LES band position bias continues for 2007-LES band position bias continues for 2007-

20082008 Significantly worse for ARWSignificantly worse for ARW

Bias degradingBias degrading Bias must be removed before ensemble can reach Bias must be removed before ensemble can reach

full potentialfull potential Bias appears linked to overly strong low Bias appears linked to overly strong low

level wind fields in ARWlevel wind fields in ARW Numerous sensitivities show that this bias may be Numerous sensitivities show that this bias may be

core (and not physics) dependentcore (and not physics) dependent Version 3 of WRF ARW improves simulationsVersion 3 of WRF ARW improves simulations


Future WorkFuture Work Expand study to additional casesExpand study to additional cases

Similar results so far for 25JAN2008Similar results so far for 25JAN2008

Migrate local BGM WRF run to version 3Migrate local BGM WRF run to version 3 WRF-EMS version 3 expected this fallWRF-EMS version 3 expected this fall Determine optimal local settings for LESDetermine optimal local settings for LES

Hone in on reason for version 2Hone in on reason for version 23 change in ARW 3 change in ARW performanceperformance

Perform 2008-2009 case studiesPerform 2008-2009 case studies


AcknowledgementsAcknowledgements

Stephen Jascourt (UCAR/COMET)Stephen Jascourt (UCAR/COMET) Jimy Dudhia (UCAR)Jimy Dudhia (UCAR) Robert Rozumalski (NWS/OCWWS) Robert Rozumalski (NWS/OCWWS)

……for guidance on model formulations, for guidance on model formulations, model changes and suggestions for model changes and suggestions for sensitivity simulationssensitivity simulations

the 10th annual northeast regional operational workshop, albany, ny northeast regional ensemble...

Documents

ny arw

ny slide

nmm arw

southward bias

event 10feb2008 slide

band location ensemble

apparent arw

band sinks