the challenge of convective forecasting “predictability does not necessarily imply ability to...
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The Challenge of Convective Forecasting
“Predictability does not necessarily imply ability to predict”
ASP/MMM Colloquium July 10-21, 2006
Morris Weisman NCAR/MMM
Introduction/Motivation
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“Weather prediction is the principal reason for the support which we are given by our fellow citizens……
I believe it is time for convective-storm scientists to apply our knowledge to this purpose and to subject our products to its discipline……
……..The task is not trivial…..”
Doug Lilly, Q. J. of the Royal Meteor. Soc., 1990
Numerical prediction of thunderstorms—has its time come?
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QuickTime™ and aBMP decompressor
are needed to see this picture.
Initialized 05 Nov 2005 00 UTC
Reflectivity forecast Composite NEXRAD Radar
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Reflectivity forecast Composite NEXRAD Radar
06 Nov 2005
31 h valid 07 UTC 08 UTC
(tiff)
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Evansville Tornado ???
Well, actually from Greg Thompson’s Web page
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WRF Modeling System
Obs Data,Analyses
Post Processors,Verification
WRF Software Infrastructure
Dynamic Cores
ARW Core
NMM Core…
Standard Physics Interface
Physics Packages
StaticInitialization
3DVAR DataAssimilation
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• Terrain-following hydrostatic pressure vertical coordinate
• Arakawa C-grid, two-way interacting nested grids (soon)
• 3rd order Runge-Kutta split-explicit time differencing
• Conserves mass, momentum, entropy, and scalars using flux form prognostic equations
• 5th order upwind or 6th order centered differencing for advection
• Multiple physics combinations (many converted from MM5), Noah and RUC land-surface submodels
WRF-ARW Mass Coordinate Core
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WRF Model Physics
• “Plug-compatible” interface defined for physics modules
• Physics options implemented in WRF:
– Microphysics: Kessler-type (no-ice) Lin et al. (graupel
included),WSM6 NCEP Cloud3, Cloud5,
Ferrier– Cumulus Convection: New Kain-Fritsch, Grell Ensemble
Betts-Miller-Janjic – Shortwave Radiation: Dudhia (MM5), Goddard, GFDL– Longwave Radiation: RRTM, GFDL– Turbulence: Prognostic TKE,
Smagorinsky, constant diffusion– PBL: MRF, MYJ, YSU– Surface Layer: Similarity theory, MYJ– Land-Surface: 5-layer soil model, RUC LSM
Noah unified LSM, HRLDAS
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Idealized WRF Simulations
PBL LES, x = 50 m Density current, x = 100 m
Supercell thunderstorm, x = 1 km
Mountain wave, x = 20 km
Baroclinic wave, x = 100 km
5 min 10 min 15 min
(Chin-Hoh Moeng)
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WRF Realtime Convective Forecasting
May 1 – July 31 4 km 00 UTC -- 36h
2003, 2004, 2005
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00Z 10 June – 13Z 11 June 2003
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Real-time WRF 4 km BAMEX Forecast
Composite NEXRAD RadarReflectivity forecast
Initialized 00 UTC 9 June 03
QuickTime™ and aBMP decompressor
are needed to see this picture.
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Real-time WRF 4 km BAMEX Forecast
Initialized 00 UTC 10 June 03
Reflectivity forecast Composite NEXRAD Radar
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Realtime WRF 4 km BAMEX Forecast
Composite NEXRAD Radar30 h Reflectivity Forecast
Missed
Valid 6/12/03 06Z
= MCS “position”
Correspond
Correspond
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1 10 100 km
Cumulus ParameterizationResolved Convection
LES PBL Parameterization
Two Stream Radiation3-D Radiation
Model Physics in High Resolution NWP
Physics“No Man’s Land”
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4 km? 2 km?BAMEX OBS, Reflectivity
100m?
How much resolution do we need??George Bryan NCAR/MMM (Thursday morning)
What does it take to simulate convection??
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ARW2 BREF
NMM4ARW4
0500 UTC 29 April 2005: 1 km model reflectivity, NEXRAD BREF
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Power Spectra for 3 h Precipitation
12Z forecasts,15-18 Z accum precip,valid 4 June 2002
(From Mike Baldwin and Matt Wandishin, NOAA/NSSL)
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NEXRAD Composite
Reisner Scheme SB2004 Scheme
WSM-6 SchemeLin, et al. Scheme
4 km WRF-ARW12 h reflectivity forecast, Valid 10 June 2003 12 Z
Column Max Reflectivity (dBZ)
Does microphysics matter at all???
Axel Seifert (DWD), Friday morning
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4 km WRF 12 h Precipitation Forecast
NCEP Stage 4 Data
Reisner Scheme SB2004 Scheme
WSM-6 SchemeLin, et al. Scheme
Valid 10 June 2003 12 Z
Total Precipitation (mm)
(Axel Seifert, 2004)
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Reisner
Lin WSM-6
SB2004
12 h Surface Theta
Cold Pools??
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Are we properly representing the structure and evolution of the PBL??
Jack Kain (NSSL) PBL observations and forecasting issues: Friday afternoon
Bjorn Stevens (UCLA), PBL theory and parameterization: Monday Morning
Fei Chen (NCAR/RAL), Land surface modeling: Monday Afternoon
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Sounding comparison: 24h forecast valid 00Z 18 May at DDC
ARW4
NMM4
Too dry in PBL, too moist above; Where is the PBL top?
Good forecast…
Model Raob
Model Raob
MYJ
YSU
(Jack Kain, NSSL)
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Sounding comparison: 24h forecast valid 00Z 24 May at DDC
ARW4
NMM4
Good forecast…
PBL too shallow, cold, & moist…clouds just broke up!
Model Raob
Model Raob
MYJ
YSU
(Jack Kain, NSSL)
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Black Contours: Surface Mixing Ratio Colors: Surface Volumetric Soil Moisture
(b) 4-km HRLDAS fields (a) 40-km EDAS soil fields
Similar large-scale heterogeneity in OK EDAS is wetter along the TX dryline
dry wet
Land Surface Sensitivities:(19 June 2002 IHOP, Stan Trier)
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Trier, Chen and Manning, 2004.
Coarse resolution soil moisture High resolution soil moisture
3 hour precip.
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Theoretical Predictability Limits??
Thunderstorms (~10 km): ~ 1h Convective Systems (300 km): ~12 h
Subsynoptic waves (~1200 km): ~1.5 days
Lorenz, 1969Atmos. Energy Spectrum
Predictability Limit for given scale
Scale (km)
Error spectrum at given time
Rich Rotunno (NCAR/MMM) Tuesday morning (wk 2)
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What can data assimilation offer us??
Chris Snyder, (NCAR/MMM) Fundamentals of data assimilation, Tuesday morning
David Dowell (NCAR/MMM-RAL) Ensemble Kalman Filters, Wednesday morning
Jenny Sun (NCAR/MMM-RAL) The VDRAS system, Thursday morning
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Three hour forecast
(4DVar data assimilation system, Juanzhen Sun)
Observed reflectivity
(KVNX radar)
IHOP case, June 12, 2002
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EnKF assimilation of KOUN NEXRAD data (50 ensemble members)
Dowell et al. 2004
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What is the future for Mesoscale Observations?
Howard Bluestein (OU) Thursday morning (wk 2)
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Sensitivity studies indicate that moisture is the key observable for improved short range forecasts of hazardous weather.
REFRACTIVITY GPS PRECIPITABLE WATER
WATER VAPOR DIAL LIDAR
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POLARIMETRIC RADAR OBSERVATIONS
Particle discrimination
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So, will we ever be able to predict this….
….hours,days in advance???
Lou Wicker (NSSL) Tuesday afternoon (wk 2)
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Hurricane Frances Reflectivity near Landfall
Melbourne Radar
48 h forecast from 4 km WRF valid at 00Z Sept 5
Chris Davis (NCAR/MMM), Wednesday (wk 2)
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Convective storms/systems
Morris Weisman (NCAR/MMM)
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X0600 UTC 10 June, 2003
11 June, 2003
0540 UTC 10 June, 2003
Upscale Growth of Convection
Chris Davis (NCAR/MMM) Bow echoes
MCV
MCSs
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Synoptic and mesoscale influences……
Lance Bosart (SUNY), Howard Bluestein (OU), Stan Trier (NCAR/MMM), Steve Weiss (SPC)
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Colloquium Goals:
•What are our current capabilities related to convective NWP in the 0-36 h range?
•What are our current limitations? (numerics, physics, observations, assimilation techniques,computer capacity…i.e.,where do we need research?)
What can we hope to achieve? e.g., predictability!!!