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**Some Applications of Indices to Forecasting**

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

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**Outline Make note of several “indices”**

Discuss utility & attributes of indices (+ / -) Show several examples of testing indices for operations – implications for training

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**A cornucopia of “indices”**

Lifted Index (LI)* Total Totals (TT) K Index (KI) Showalter Index (SI) Severe Weather Threat (SWEAT) CAP Strength (700 mb LI) Lapse Rate (LR)* Relative Humidity (RH)* * Can be calculated over many different layers/levels/parcels

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**A cornucopia of “indices”**

Lifted Index (LI)* Total Totals (TT) K Index (KI) Showalter Index (SI) Severe Weather Threat (SWEAT) CAP Strength (700 mb LI) Lapse Rate (LR)* Relative Humidity (RH)* Lifted Condensation Level (LCL)* Level of Free Convection (LFC)* Equilibrium Level (EL)* Wet Bulb Zero (WBZ) Melting Level (MLT) Warm Cloud Depth (WCD)* Precipitable Water (PW)* Equivalent Potential Temperature (e)* Moisture Flux “Convergence” (MFC)* * Can be calculated over many different layers/levels/parcels

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**A cornucopia of “indices”**

Lifted Index (LI)* Convective Available Potential Energy (CAPE)* Total Totals (TT) Convective Inhibition (CIN)* K Index (KI) Bulk Richardson Number (BRN)* Showalter Index (SI) Bulk Richardson Number Shear (BRNSHR) Severe Weather Threat (SWEAT) Bulk Vertical Wind Shear* CAP Strength (700 mb LI) Total Vertical Wind Shear* Lapse Rate (LR)* Storm-Relative Wind* Relative Humidity (RH)* Storm-Relative Helicity (SRH)* Downdraft CAPE (DCAPE) Lifted Condensation Level (LCL)* Normalized CAPE (nCAPE)* Level of Free Convection (LFC)* Equilibrium Level (EL)* Wet Bulb Zero (WBZ) Melting Level (MLT) Warm Cloud Depth (WCD)* Precipitable Water (PW)* Equivalent Potential Temperature (e)* Moisture Flux “Convergence” (MFC)* * Can be calculated over many different layers/levels/parcels * Can be calculated over many different layers/levels/parcels

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**A cornucopia of “indices”**

Lifted Index (LI)* Convective Available Potential Energy (CAPE)* Total Totals (TT) Convective Inhibition (CIN)* K Index (KI) Bulk Richardson Number (BRN)* Showalter Index (SI) Bulk Richardson Number Shear (BRNSHR) Severe Weather Threat (SWEAT) Bulk Vertical Wind Shear* CAP Strength (700 mb LI) Total Vertical Wind Shear* Lapse Rate (LR)* Storm-Relative Wind* Relative Humidity (RH)* Storm-Relative Helicity (SRH)* Downdraft CAPE (DCAPE) Lifted Condensation Level (LCL)* Normalized CAPE (nCAPE)* Level of Free Convection (LFC)* Equilibrium Level (EL)* Wind Index (WINDEX) Wet Bulb Zero (WBZ) Dry Microburst Index (DMI) Melting Level (MLT) Theta-E Index (TEI) Warm Cloud Depth (WCD)* Microburst Day Potential Index (MDPI) Precipitable Water (PW)* Wet Microburst Severity Index (WMSI) Equivalent Potential Temperature (e)* Moisture Flux “Convergence” (MFC)* * Can be calculated over many different layers/levels/parcels * Can be calculated over many different layers/levels/parcels

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**A cornucopia of “indices”**

Lifted Index (LI)* Convective Available Potential Energy (CAPE)* Total Totals (TT) Convective Inhibition (CIN)* HI = Haines Index* HMI = Hybrid Microburst Index K Index (KI) Bulk Richardson Number (BRN)* LSI = Lid Strength Index Showalter Index (SI) Bulk Richardson Number Shear (BRNSHR) DCI = Deep Convective Index TQ Index = for “low-topped instability” Severe Weather Threat (SWEAT) Bulk Vertical Wind Shear* CAP Strength (700 mb LI) Total Vertical Wind Shear* Lapse Rate (LR)* Storm-Relative Wind* Relative Humidity (RH)* Storm-Relative Helicity (SRH)* Downdraft CAPE (DCAPE) Lifted Condensation Level (LCL)* Normalized CAPE (nCAPE)* Level of Free Convection (LFC)* Equilibrium Level (EL)* Wind Index (WINDEX) Wet Bulb Zero (WBZ) Dry Microburst Index (DMI) Melting Level (MLT) Theta-E Index (TEI) Warm Cloud Depth (WCD)* Microburst Day Potential Index (MDPI) Precipitable Water (PW)* Wet Microburst Severity Index (WMSI) Equivalent Potential Temperature (e)* Moisture Flux “Convergence” (MFC)* * Can be calculated over many different layers/levels/parcels

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**A cornucopia of “indices”**

Lifted Index (LI)* Convective Available Potential Energy (CAPE)* Total Totals (TT) Convective Inhibition (CIN)* HI = Haines Index* HMI = Hybrid Microburst Index K Index (KI) Bulk Richardson Number (BRN)* LSI = Lid Strength Index Showalter Index (SI) Bulk Richardson Number Shear (BRNSHR) DCI = Deep Convective Index TQ Index = for “low-topped instability” Severe Weather Threat (SWEAT) Bulk Vertical Wind Shear* CAP Strength (700 mb LI) Total Vertical Wind Shear* Indices of Indices (“Inbreeding”) Lapse Rate (LR)* Storm-Relative Wind* Energy-Helicity Index (EHI)* Relative Humidity (RH)* Storm-Relative Helicity (SRH)* Vorticity Generation Parameter (VGP)* Downdraft CAPE (DCAPE) Supercell Composite Parameter (SCP)* Lifted Condensation Level (LCL)* Normalized CAPE (nCAPE)* Significant Tornado Parameter (STP)* Level of Free Convection (LFC)* Significant Hail Parameter (SHIP) Equilibrium Level (EL)* Wind Index (WINDEX) Significant Severe Parameter (SSP) Wet Bulb Zero (WBZ) Dry Microburst Index (DMI) Strong Tornado Parameter (STP) Melting Level (MLT) Theta-E Index (TEI) Warm Cloud Depth (WCD)* Microburst Day Potential Index (MDPI) Precipitable Water (PW)* Wet Microburst Severity Index (WMSI) Equivalent Potential Temperature (e)* Moisture Flux “Convergence” (MFC)* * Can be calculated over many different layers/levels/parcels

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**A cornucopia of “indices”**

Lifted Index (LI)* Convective Available Potential Energy (CAPE)* Total Totals (TT) Convective Inhibition (CIN)* HI = Haines Index* HMI = Hybrid Microburst Index K Index (KI) Bulk Richardson Number (BRN)* LSI = Lid Strength Index Showalter Index (SI) Bulk Richardson Number Shear (BRNSHR) DCI = Deep Convective Index TQ Index = for “low-topped instability” Severe Weather Threat (SWEAT) Bulk Vertical Wind Shear* CAP Strength (700 mb LI) Total Vertical Wind Shear* Indices of Indices (“Inbreeding”) Lapse Rate (LR)* Storm-Relative Wind* Energy-Helicity Index (EHI)* Relative Humidity (RH)* Storm-Relative Helicity (SRH)* Vorticity Generation Parameter (VGP)* Vorticity Generation Parameter (VGP)* Downdraft CAPE (DCAPE) Supercell Composite Parameter (SCP) Supercell Composite Parameter (SCP)* Lifted Condensation Level (LCL)* Normalized CAPE (nCAPE)* Significant Tornado Parameter (STP)* Level of Free Convection (LFC)* Significant Hail Parameter (SHIP) Equilibrium Level (EL)* Wind Index (WINDEX) Significant Severe Parameter (SSP) Wet Bulb Zero (WBZ) Dry Microburst Index (DMI) Strong Tornado Parameter (STP) Melting Level (MLT) Theta-E Index (TEI) Warm Cloud Depth (WCD)* Microburst Day Potential Index (MDPI) Precipitable Water (PW)* Wet Microburst Severity Index (WMSI) Equivalent Potential Temperature (e)* Mesoscale Convective System Forecast Index (MCS Index) a recent index published in WAF (2007) Moisture Flux “Convergence” (MFC)* This list is not nearly exhaustive! * Can be calculated over many different layers/levels/parcels

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**What’s a forecaster to do?**

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**Outline Make note of several “indices”**

Discuss utility & attributes of indices (+ / -) Show several examples of testing indices for operations – implications for training

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**Attributes of indices Doswell and Schultz (2006)**

“On the Use of Indices and Parameters in Forecasting Severe Storms” Electronic Journal of Severe Storms Meteorology

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**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

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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

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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

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**The Edge: 20 Jun 2006 – Rushville, NE**

Tornadic left-moving supercell LSCP (1-EF1)

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**The Edge: 16 Sep 2006 – Rogers, MN**

(1-EF2)

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**The Edge: 28 Feb 2007 – Eastern KS**

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

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**Outline Make note of several “indices”**

Discuss utility & attributes of indices (+ / -) Show several examples of testing indices for operations – implications for training

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**Example of testing an index**

Jirak and Cotton (2007, WAF) MCS index for conditional development of MCSs Function of “best” LI, 0-3km shear, and 700mb Tadv Convert terms to standard normal and summed Appears to be physically based Developed using NARR data Tested at WFO Rapid City and found problems Operational datasets produced different results Didn’t implement at our office

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**MCS index on WES Image = MCS index White lines = 700mb Tadv**

MCS index and 700mb Tadv looked very similar Was “verified” with 20 cases

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**MCS index testing Let LI vary from +3 to -12 (C)**

Let shear vary from 0 to 25 (m s-1) Let Tadv vary from -1 to +2 (C hr-1) Mean Std Dev Means and standard deviations based on NARR dataset (JC07).

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**Three terms of MCS index**

Using JC07’s equation and reasonable ranges for the 3 terms Ideally all 3 lines should be the same

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**MCS index summary LI component -2 to 2 Shear component -2 to 2**

Tadv component -4 to 6 (should be -2 to 2) NARR data underrepresented the operational Tadv range MCS index basically proxy for 700mb Tadv Conclusion: not suitable for operations (authors updating to use stddev of range)

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**Outline Make note of several “indices”**

Discuss utility & attributes of indices (+ / -) Show several examples of testing indices for operations – implications for training

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**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)

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**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

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Versions of the STP

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Versions of the STP

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Versions of the STP If you use them, know your indices!

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**Outline Make note of several “indices”**

Discuss utility & attributes of indices (+ / -) Show several examples of testing indices for operations – implications for training

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**Supercell Composite Parameter (SCP)**

Function of MUCAPE, Eff. Shear, and Eff. SRH Can run similar tests as for the STP Testing suggests SCP can be misleading

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SCP Potential Pitfall Dominant right-mover

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**Modeling Results SRH (RM) = 62 SRH (LM) = -226**

Hodograph didn’t turn enough in lowest 36 km to strongly favor LM. Environmental heterogeneity and low-level wind variability also factors.

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**Outline Make note of several “indices”**

Discuss utility & attributes of indices (+ / -) Show several examples of testing indices for operations – implications for training

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**Example of coord system sensitivity**

SWEAT Index (SW): May 2001 OK case SW = 331 What if 850 wspd = 15 kts? (SW = 429) Now what if wdir 30 to left (SW = 331)

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**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!

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**SCM: Excel vs. BUFKIT 12-kt difference between the two!**

275° 28 kts 12-kt difference between the two! …but AWIPS is okay

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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

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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.

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