Some Applications of Indices to Forecasting

12th Great Divide Workshop, 10/7/2008Matthew J. Bunkers, SOO Rapid City,

SD

Outline

• Make note of several “indices”

• Discuss utility & attributes of indices (+ / -)

• Show several examples of testing indices for operations – implications for training

A cornucopia of “indices”

K Index (KI)

Total Totals (TT)

Severe Weather Threat (SWEAT)

Lifted Index (LI)*

Showalter Index (SI)

Lapse Rate (LR)*

* Can be calculated over many different layers/levels/parcels

CAP Strength (700 mb LI)

Relative Humidity (RH)*

A cornucopia of “indices”

Lifted Condensation Level (LCL)*

Level of Free Convection (LFC)*

Equilibrium Level (EL)*

* Can be calculated over many different layers/levels/parcels

Moisture Flux “Convergence” (MFC)*

Equivalent Potential Temperature (e)*

Precipitable Water (PW)*

Warm Cloud Depth (WCD)*

Wet Bulb Zero (WBZ)

Melting Level (MLT)

K Index (KI)

Total Totals (TT)

Severe Weather Threat (SWEAT)

Lifted Index (LI)*

Showalter Index (SI)

Lapse Rate (LR)*

CAP Strength (700 mb LI)

Relative Humidity (RH)*

A cornucopia of “indices”Convective Available Potential Energy (CAPE)*Convective Inhibition (CIN)*

Bulk Richardson Number (BRN)*

Storm-Relative Helicity (SRH)*

Bulk Vertical Wind Shear*

Total Vertical Wind Shear*

Storm-Relative Wind*

Downdraft CAPE (DCAPE)

* Can be calculated over many different layers/levels/parcels

Normalized CAPE (nCAPE)*

Bulk Richardson Number Shear (BRNSHR)

* Can be calculated over many different layers/levels/parcels

Lifted Condensation Level (LCL)*

Level of Free Convection (LFC)*

Equilibrium Level (EL)*

Moisture Flux “Convergence” (MFC)*

Equivalent Potential Temperature (e)*

Precipitable Water (PW)*

Warm Cloud Depth (WCD)*

Wet Bulb Zero (WBZ)

Melting Level (MLT)

K Index (KI)

Total Totals (TT)

Severe Weather Threat (SWEAT)

Lifted Index (LI)*

Showalter Index (SI)

Lapse Rate (LR)*

CAP Strength (700 mb LI)

Relative Humidity (RH)*

A cornucopia of “indices”

* Can be calculated over many different layers/levels/parcels

Dry Microburst Index (DMI)

Theta-E Index (TEI)

Wind Index (WINDEX)

Wet Microburst Severity Index (WMSI)

Microburst Day Potential Index (MDPI)

* Can be calculated over many different layers/levels/parcels

Convective Available Potential Energy (CAPE)*Convective Inhibition (CIN)*

Bulk Richardson Number (BRN)*

Storm-Relative Helicity (SRH)*

Bulk Vertical Wind Shear*

Total Vertical Wind Shear*

Storm-Relative Wind*

Downdraft CAPE (DCAPE)

Normalized CAPE (nCAPE)*

Bulk Richardson Number Shear (BRNSHR)

Lifted Condensation Level (LCL)*

Level of Free Convection (LFC)*

Equilibrium Level (EL)*

Moisture Flux “Convergence” (MFC)*

Equivalent Potential Temperature (e)*

Precipitable Water (PW)*

Warm Cloud Depth (WCD)*

Wet Bulb Zero (WBZ)

Melting Level (MLT)

K Index (KI)

Total Totals (TT)

Severe Weather Threat (SWEAT)

Lifted Index (LI)*

Showalter Index (SI)

Lapse Rate (LR)*

CAP Strength (700 mb LI)

Relative Humidity (RH)*

* Can be calculated over many different layers/levels/parcels

LSI = Lid Strength IndexDCI = Deep Convective IndexTQ Index = for “low-topped

instability”

HI = Haines Index*HMI = Hybrid Microburst Index

A cornucopia of “indices”

Dry Microburst Index (DMI)

Theta-E Index (TEI)

Wind Index (WINDEX)

Wet Microburst Severity Index (WMSI)

Microburst Day Potential Index (MDPI)

Convective Available Potential Energy (CAPE)*Convective Inhibition (CIN)*

Bulk Richardson Number (BRN)*

Storm-Relative Helicity (SRH)*

Bulk Vertical Wind Shear*

Total Vertical Wind Shear*

Storm-Relative Wind*

Downdraft CAPE (DCAPE)

Normalized CAPE (nCAPE)*

Bulk Richardson Number Shear (BRNSHR)

Lifted Condensation Level (LCL)*

Level of Free Convection (LFC)*

Equilibrium Level (EL)*

Moisture Flux “Convergence” (MFC)*

Equivalent Potential Temperature (e)*

Precipitable Water (PW)*

Warm Cloud Depth (WCD)*

Wet Bulb Zero (WBZ)

Melting Level (MLT)

K Index (KI)

Total Totals (TT)

Severe Weather Threat (SWEAT)

Lifted Index (LI)*

Showalter Index (SI)

Lapse Rate (LR)*

CAP Strength (700 mb LI)

Relative Humidity (RH)*

A cornucopia of “indices”

Energy-Helicity Index (EHI)*

Vorticity Generation Parameter (VGP)*

Supercell Composite Parameter (SCP)*

Significant Tornado Parameter (STP)*

Significant Hail Parameter (SHIP)

* Can be calculated over many different layers/levels/parcels

Significant Severe Parameter (SSP)

Strong Tornado Parameter (STP)

Indices of Indices (“Inbreeding”)

LSI = Lid Strength IndexDCI = Deep Convective IndexTQ Index = for “low-topped

instability”

HI = Haines Index*HMI = Hybrid Microburst Index

Dry Microburst Index (DMI)

Theta-E Index (TEI)

Wind Index (WINDEX)

Wet Microburst Severity Index (WMSI)

Microburst Day Potential Index (MDPI)

Convective Available Potential Energy (CAPE)*Convective Inhibition (CIN)*

Bulk Richardson Number (BRN)*

Storm-Relative Helicity (SRH)*

Bulk Vertical Wind Shear*

Total Vertical Wind Shear*

Storm-Relative Wind*

Downdraft CAPE (DCAPE)

Normalized CAPE (nCAPE)*

Bulk Richardson Number Shear (BRNSHR)

Lifted Condensation Level (LCL)*

Level of Free Convection (LFC)*

Equilibrium Level (EL)*

Moisture Flux “Convergence” (MFC)*

Equivalent Potential Temperature (e)*

Precipitable Water (PW)*

Warm Cloud Depth (WCD)*

Wet Bulb Zero (WBZ)

Melting Level (MLT)

K Index (KI)

Total Totals (TT)

Severe Weather Threat (SWEAT)

Lifted Index (LI)*

Showalter Index (SI)

Lapse Rate (LR)*

CAP Strength (700 mb LI)

Relative Humidity (RH)*

A cornucopia of “indices”

Vorticity Generation Parameter (VGP)*

Supercell Composite Parameter (SCP)

This list is not nearly exhaustive!

K Index (KI)

Total Totals (TT)

Severe Weather Threat (SWEAT)

Lifted Index (LI)*

Showalter Index (SI)

Lapse Rate (LR)*

CAP Strength (700 mb LI)

Relative Humidity (RH)*

Lifted Condensation Level (LCL)*

Level of Free Convection (LFC)*

Equilibrium Level (EL)*

* Can be calculated over many different layers/levels/parcels

Moisture Flux “Convergence” (MFC)*

Equivalent Potential Temperature (e)*

Precipitable Water (PW)*

Warm Cloud Depth (WCD)*

Wet Bulb Zero (WBZ)

Melting Level (MLT)

Convective Available Potential Energy (CAPE)*Convective Inhibition (CIN)*

Bulk Richardson Number (BRN)*

Storm-Relative Helicity (SRH)*

Bulk Vertical Wind Shear*

Total Vertical Wind Shear*

Storm-Relative Wind*

Downdraft CAPE (DCAPE)

Normalized CAPE (nCAPE)*

Bulk Richardson Number Shear (BRNSHR)

Dry Microburst Index (DMI)

Theta-E Index (TEI)

Wind Index (WINDEX)

Wet Microburst Severity Index (WMSI)

Microburst Day Potential Index (MDPI)

Energy-Helicity Index (EHI)*

Vorticity Generation Parameter (VGP)*

Supercell Composite Parameter (SCP)*

Significant Tornado Parameter (STP)*

Significant Hail Parameter (SHIP)

Significant Severe Parameter (SSP)

Strong Tornado Parameter (STP)

Indices of Indices (“Inbreeding”)

LSI = Lid Strength IndexDCI = Deep Convective IndexTQ Index = for “low-topped

instability”

HI = Haines Index*HMI = Hybrid Microburst Index

Mesoscale Convective System Forecast Index (MCS Index) a recent index published in WAF (2007)

What’s a forecaster to do?

Outline

• Make note of several “indices”

• Discuss utility & attributes of indices (+ / -)

• Show several examples of testing indices for operations – implications for training

Attributes of indices

Benefits of indices

• Can summarize large amounts of data

• Can quickly draw attention to “critical” areas for further diagnosis

– Both are attractive when under time pressure

Index limitations

• Not necessarily forecast parameters; may be diagnostic (e.g., SPC meso page)– Diagnostic variables give current state

(≠ /t), where = STP, SCP, CAPE, etc.

• Most indices are not rigorously developed or validated – arbitrarily combined variables

Index limitations

• Can lead to faulty perceptions of atmosphere via over-simplification– Little value in isolation; different combos can

produce similar values– Flavor of the parameter? (e.g., EHI and its inputs)– Constituents can evolve quasi-independently

• Action often occurs at “The Edge” – next three slides

The Edge: 20 Jun 2006 – Rushville, NE

LSCP

Tornadic left-moving supercell

(1-EF1)

The Edge: 16 Sep 2006 – Rogers, MN(1-EF2)

The Edge: 28 Feb 2007 – Eastern KS

(1-EF4)

Important to train new forecasters not to focus on bulls-eyes.

Outline

• Make note of several “indices”

• Discuss utility & attributes of indices (+ / -)

• Show several examples of testing indices for operations – implications for training

The STP index

• Thompson et al. (2003, WAF)– Significant Tornado Parameter (STP)

• Mean-layer CAPE (MLCAPE, lowest 100mb)• 0-6km shear vector magnitude (SHR6)• 0-1km storm-relative helicity (SRH1)• Mean layer LCL (MLLCL, lowest 100mb)

Let’s test this

• Estimate valid ranges and calculate each term– For example: MLCAPE ~ 100 to 5000 J kg-1

• Term 1 thus ranges from 0.1 to 5– (100/1000) = 0.1– (5000/1000) = 5

Versions of the STP

Versions of the STP

Versions of the STP

If you use them, know your indices!

Outline

• Make note of several “indices”

• Discuss utility & attributes of indices (+ / -)

• Show several examples of testing indices for operations – implications for training

Example of coord system sensitivity

Supercell motion example: BUFKIT

• Bunkers et al. (2000)– Non-weighted MW for

supercell motion, every 500 meters

• BUFKIT– Uses ALL data for MW;

produces low-level bias– Supercell motion often

too slow…so beware of BUFKIT algorithm!

SCM: Excel vs. BUFKIT

12-kt difference between the two!

…but AWIPS is okay

275° 28 kts

Summary for indices

• Look at the raw data (e.g., surface maps, soundings, 0-1km shear, MLLCL, etc.)

• View the indices’ constituent components (e.g., 4-panel mode)…”STP = 2 means what?”

• Test new indices before implementing them in operations (e.g., the MCS index)– Folly to develop indices away from operations

One final thought

“The author’s most regrettable severe storm forecast mistakes have arisen from ignoring data that were relevant to the daily diagnosis…and/or failing to complete the diagnosis on what initially appeared to be a benign weather day.”

– Al Moller (2001, Severe Convective Storms Monograph)

• Analysis and diagnosis of observational data is critical – yet this has become a lost art.