Some Applications of Indices to Forecasting 12 th Great Divide Workshop, 10/7/2008 Matthew J....

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)*


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)


Lifted Index (LI)*


Lapse Rate (LR)*



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)


Normalized CAPE (nCAPE)*

Bulk Richardson Number Shear (BRNSHR)









Wet Bulb Zero (WBZ)

Melting Level (MLT)

K Index (KI)

Total Totals (TT)


Lifted Index (LI)*


Lapse Rate (LR)*





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)*
















Wet Bulb Zero (WBZ)

Melting Level (MLT)

K Index (KI)

Total Totals (TT)


Lifted Index (LI)*


Lapse Rate (LR)*




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

instability”

HI = Haines Index*HMI = Hybrid Microburst Index



Theta-E Index (TEI)

Wind Index (WINDEX)



















Wet Bulb Zero (WBZ)

Melting Level (MLT)

K Index (KI)

Total Totals (TT)


Lifted Index (LI)*


Lapse Rate (LR)*




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”)


instability”



Theta-E Index (TEI)

Wind Index (WINDEX)



















Wet Bulb Zero (WBZ)

Melting Level (MLT)

K Index (KI)

Total Totals (TT)


Lifted Index (LI)*


Lapse Rate (LR)*





Supercell Composite Parameter (SCP)

This list is not nearly exhaustive!

K Index (KI)

Total Totals (TT)


Lifted Index (LI)*


Lapse Rate (LR)*











Wet Bulb Zero (WBZ)

Melting Level (MLT)











Theta-E Index (TEI)

Wind Index (WINDEX)



Energy-Helicity Index (EHI)*


Supercell Composite Parameter (SCP)*

Significant Tornado Parameter (STP)*

Significant Hail Parameter (SHIP)

Significant Severe Parameter (SSP)

Strong Tornado Parameter (STP)

Indices of Indices (“Inbreeding”)


instability”


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

What’s a forecaster to do?

Outline




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




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

If you use them, know your indices!

Outline




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.

Some Applications of Indices to Forecasting 12 th Great Divide Workshop, 10/7/2008 Matthew J....

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