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Some Applications of Indices to Forecasting 12 th 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” 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)*

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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)*

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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)*

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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)*

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* Can be calculated over many different layers/levels/parcels LSI = Lid Strength Index DCI = Deep Convective Index TQ 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)*

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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 Index DCI = Deep Convective Index TQ 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)*

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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 Index DCI = Deep Convective Index TQ 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)

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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 LSCP Tornadic left-moving supercell (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 (1-EF4) 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 T adv 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 T adv MCS index and 700mb T adv 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 ) Std Dev Mean 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 T adv component -4 to 6 (should be -2 to 2) NARR data underrepresented the operational T adv range – MCS index basically proxy for 700mb T adv – 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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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 3 6 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! …but AWIPS is okay 275° 28 kts

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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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