(Updated with latest metrics and definitions, Version 6, December 2019). The QI or Quality Index is a proposed method to quantify the overall quality of a storm chasing event using objective criteria. The term "quality" itself is subjective, but we will define and use the following factors to determine the final QI: daytime photogenic tornadoes, storm structure, lightning, terrain, road network, forecast lead time, storm impacts, rare features and human impacts.
The following is a screen capture of the most recent application (v6) of the QIS formula to a selection of chase days. QIS of 10 and up is "good", 20 and up is "exceptional":
The "QIS Base" is the calculated value before considering negative human impact metrics (what the QIS would have been if the tornadoes had not hit anything).
QI: Definitions & metrics
ABOVE: Examples of daytime photogenic tornadoes. Low contrast does not disqualify a tornado from being considered "photogenic" if the low contrast is due to viewing from great distances and not from heavy precipitation surrounding the tornado.
TargetLevel Quality Index (QIS)
The TargetLevel Quality Index or QIS considers the quality of a single chase target, either primary or secondary. The QIS evaluates the best possible outcome of a reasonable chase involving one or more storms within reach of that target. The QIS can cover multiple storms if all of them were observed by the majority of chasers in the target (example: May 5, 2007 involved tornadoes on 3 different storms in one central Kansas target).
The proposed formula (current v6) is as follows:
QIS = ((DPT*300)+(FL*100)+(H*500)+(TF*50)+(RF*100)+(R*100)+(TRF*100)+(D*150)+(I*350)+(FT*500)+(MD*1200)+(L*100)+(T*150)+(HT*70)+(DPTmins*1.1)*(60speed)+(Smins/30)*(60speed))/100
EventLevel Quality Index (QIE)
The EventLevel Quality Index or QIE is the average of the QIS for all primary targets. If secondary targets are present, the QIE is the weighted mean of the primary targets average QIS (weighted at 75%) and the secondary targets average QIS (weighted at 25%).
Seasonal or Monthly Quality Index (QIY or QIM)
Seasonal or yearly QIs are simply calculated as the sum of QIE for all dates in the period. The larger the QIY or QIM, the better the season, month or other defined period.
Javascript Calculator
Online QIS calculator is available here:
QIS Calculator
Spreadsheet formula
You can download an OpenOffice Calc spreadsheet file containing the formula here:
qualitystormsv6.ods
The formula in spreadsheet form is as follows:
OpenOffice Calc:
=ROUND((((C2*300)+(J2*100)+(K2*100)+(L2*100)+(M2*100)+(N2*100)+(O2*100)+(W2*100)+(X2*100)+(U2*100)+(V2*500)+(P2*100)+(Q2*150)+(R2*350)+(S2*500)+(T2*1200)+(D2*100)+(H2*150)+(I2*5)+(E2*1.1)*(60G2)+(F2/30)*(60G2))/100))
Excel:
=ROUND((((C2*300)+(J2*100)+(K2*100)+(L2*100)+(M2*100)+(N2*100)+(O2*100)+(W2*100)+(X2*100)+(U2*100)+(V2*500)+(P2*100)+(Q2*150)+(R2*350)+(S2*500)+(T2*1200)+(D2*100)+(H2*150)+(I2*5)+(E2*1.1)*(60G2)+(F2/30)*(60G2))/100), 0)
The following is a screen capture of the most recent application (v6) of the QIS formula to a selection of chase days. QIS of 10 and up is "good", 20 and up is "exceptional":
The "QIS Base" is the calculated value before considering negative human impact metrics (what the QIS would have been if the tornadoes had not hit anything).
QI: Definitions & metrics
 Standard chaser positions: The most common stormviewing positions employed by chasers, mainly from south, east and north of a mesocyclone. Distance from the storm is not a factor considered by the QI.
 Primary targets (PT): Traditionallyevident targets where the majority of chasers ended up. PTs include but are not limited to dryline bulges, warm fronts, triple points, outflow boundaries, boundary intersections, upperlevel speed maxima, etc. There can be multiple primary targets in a single event (common, for example, during big outbreaks).
 Secondary targets (ST): Nontraditional target areas such as coldcore, DVCZ, upslope or Midwest warm/stationary front storms where only a small percentage of chasers deliberately target. Note that these types of targets can become primary if the traditional target areas are too marginal or not present. Secondary targets that become primary should be counted as PTs in QI calculations.
 Daytime photogenic tornado (DPT): The number of daytime tornadoes with complete structure consisting of a funnel and/or debris spanning at least 75% of the distance from ground to cloud base, clearly visible to observers at least 180 degrees surrounding the tornado (standard chaser positions). Photogenic tornadoes assume good visibility to all chasers in the vicinity (distance from the tornado is not considered by the QI).
ABOVE: Examples of daytime photogenic tornadoes. Low contrast does not disqualify a tornado from being considered "photogenic" if the low contrast is due to viewing from great distances and not from heavy precipitation surrounding the tornado.
 Standard tornadoes (T): The total number of tornadoes visible from standard chaser positions during a chase in one target area  including photogenic tornadoes, tornadoes at night, or lowcontrast rainwrapped tornadoes (as long as at least one edge of the condensation funnel and/or debris cloud can be discerned visually and on photos and videos).
 HP tornadoes (HT): The number of tornadoes only visible from within the notch of a highprecipitation supercell. (Tornadoes counted as HTs should not be counted in the T total)
 Good structure (S): Welldeveloped and symmetric supercell structure, including highcontrast striations, banding and inflow tails.
 Good lightning (L): Frequent, dramatic, remarkable and/or otherwise photogenic lightning accompanying the storm for at least 30 minutes.
 Terrain factor(TF):
 Good: Flat terrain with few trees or hills (example: western Kansas)
 Fair: Mostlyflat terrain with a few hills and viewing obstacles (example: eastern Kansas)
 Poor: Terrain with mostly trees and/or hills, few clear views (example: eastern Oklahoma)
 Roads factor(RF):
 Good: 1 or 2mile grid, average spacing between paved or gravel secondaries no more than 4 miles
 Fair: No grid with half or more of secondaries paved or gravel. Average distances between paved/gravel roads between 4 and 6 miles.
 Poor: Few secondary roads, most secondaries dirt. No grid with average spacing between paved/gravel routes of more than 7 miles.
 Forecast lead time(FL): Forecast lead time refers to the ability of chasers to see the event coming in enough time to make a decision to travel to the target. "Tornado potential" refers to at least a 5% SPC tornado risk or equivalent level of confidence.
 Evening before & prior: Tornado potential evident before and up to 00z model runs the previous day
 Morningof: Tornado potential only evident in morning data (day of the event).
 None: No clear tornado/supercell potential evident (mesoscale accident).
 Rare features(R):
 Multiple simultaneous tornadoes
 Sunlit tornadoes
 Audible roar
 Highcontrast mammatus covering at least 1/4 of the sky
 Prolific upward lightning from towers and/or wind turbines
 Historic (H): Tornadoes/supercells that broke records or were otherwise exceptionally rare in their strength, number or configuration. NOTE: tornadoes that caused major disasters should not be counted as historic at the same time (the "major disaster" metric covers this aspect of historical significance).
 Negatives(N):
 Problematic traffic (TRF): Traffic (from chasers, locals or both) interfered with more than 10% of the chase in terms of slow travel speeds, delays at intersections and most available pulloffs occupied.
 Damage (D): Tornadoes that produced significant damage to homes.
 Human impact: tornadoes that caused injuries (I) OR fatalities (FT).
 Major disaster (MD): tornadoes that caused destruction to more than 1/3 of a town, more than 30 homes and/or 10 or more deaths.
TargetLevel Quality Index (QIS)
The TargetLevel Quality Index or QIS considers the quality of a single chase target, either primary or secondary. The QIS evaluates the best possible outcome of a reasonable chase involving one or more storms within reach of that target. The QIS can cover multiple storms if all of them were observed by the majority of chasers in the target (example: May 5, 2007 involved tornadoes on 3 different storms in one central Kansas target).
The proposed formula (current v6) is as follows:
QIS = ((DPT*300)+(FL*100)+(H*500)+(TF*50)+(RF*100)+(R*100)+(TRF*100)+(D*150)+(I*350)+(FT*500)+(MD*1200)+(L*100)+(T*150)+(HT*70)+(DPTmins*1.1)*(60speed)+(Smins/30)*(60speed))/100
EventLevel Quality Index (QIE)
The EventLevel Quality Index or QIE is the average of the QIS for all primary targets. If secondary targets are present, the QIE is the weighted mean of the primary targets average QIS (weighted at 75%) and the secondary targets average QIS (weighted at 25%).
Seasonal or Monthly Quality Index (QIY or QIM)
Seasonal or yearly QIs are simply calculated as the sum of QIE for all dates in the period. The larger the QIY or QIM, the better the season, month or other defined period.
Javascript Calculator
Online QIS calculator is available here:
QIS Calculator
Spreadsheet formula
You can download an OpenOffice Calc spreadsheet file containing the formula here:
qualitystormsv6.ods
The formula in spreadsheet form is as follows:
OpenOffice Calc:
=ROUND((((C2*300)+(J2*100)+(K2*100)+(L2*100)+(M2*100)+(N2*100)+(O2*100)+(W2*100)+(X2*100)+(U2*100)+(V2*500)+(P2*100)+(Q2*150)+(R2*350)+(S2*500)+(T2*1200)+(D2*100)+(H2*150)+(I2*5)+(E2*1.1)*(60G2)+(F2/30)*(60G2))/100))
Excel:
=ROUND((((C2*300)+(J2*100)+(K2*100)+(L2*100)+(M2*100)+(N2*100)+(O2*100)+(W2*100)+(X2*100)+(U2*100)+(V2*500)+(P2*100)+(Q2*150)+(R2*350)+(S2*500)+(T2*1200)+(D2*100)+(H2*150)+(I2*5)+(E2*1.1)*(60G2)+(F2/30)*(60G2))/100), 0)
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