# Presentation: 108866

## A Preliminary Investigation of Supercell Longevity

- MATTHEW J. BUNKERS, JEFFREY S. JOHNSON, JASON M. GRZYWACZ, LEE J. CZEPYHA, and BRIAN A. KLIMOWSKI
*NWS Rapid City, SD*
*6**th** High Plains Conference*
*Dodge City, KS (10/9/2002 – 10/11/2002)*

## Objectives:

- Study long-lived supercell characteristics, evolution, demise, and environments (lifetimes  4 h)
- Compare and contrast with those of short-lived supercells (lifetimes  2 h)
- “*How long will supercells last on any given day?*”

## Background:

- _Kinematics_ (shear, SRH, storm-relative winds)
- _Thermodynamics_ (CAPE, CIN, LCL, relative humidity)
- _Large-scale environment_ (boundaries, forcing mechanisms, moisture/instability axes, storm mergers/interactions; convective mode)

## Data:

- 42 long-lived supercell *events*—with the majority across the northern High Plains
- 43 short-lived supercell *events*—average lifetime of all supercells  2 h per event
- 22 *moderate-lived* supercell *events* (average lifetime between 2 and 4 h)
- Sounding data (+ a few RUC soundings)

## Long-Lived SC Tracks

**Long-Lived SC Tracks**

## General Observations:(Long-lived supercells)

- 88% of the long-lived supercells were “isolated”
- All severe; 75% produced severe hail _and_ wind; 58% produced tornadoes
- Motion generally constant throughout lifetime

## Example #1

**Example #1**

-  CL  HP

- Start

- End

## Example #2

**Example #2**

-  Warm front

- Start

- End

## Example #3

**Example #3**

-  Elevated 
-    surface-based

- End

- End

- Start

- Start

## Example of Low-End Event:

- Just north of BIS.

## Characteristics of Long-Lived Supercell Demise:

- 70% weakened and/or dissipated
- 20% evolved into bows (some via mergers)
- 10% merged with other storms and lost identity
-    -------------------------------------------------
*Short-lived supercells*:  45%, 45%, 10%

## Kinematic Results:

- _Deep-layer vertical wind shear_ significantly stronger for long- vs. short-lived supercells ( = 0.0001)
*Mean 0****8-km bulk shear (*_*Long-lived*_*) = *_*36.6 m s*__*-1*_* *
*Mean 0****8-km bulk shear (Short-lived) = 21.3 m s**-1*
- _8-km storm-relative wind_ significantly stronger for long- vs. short-lived supercells ( = 0.0001)
*Mean 8-km SRW (*_*Long-lived*_*) = *_*20.5 m s*__*-1*_
*Mean 8-km SRW (Short-lived) = 12.1 m s**-1*

## Slide 14

## Slide 15

## BIS

## Contingency Table Results:(long- vs. short-lived SCs only!)

- _Optimal 0____8-km bulk shear = 30 m s_-1
- 	POD = 0.86, FAR = 0.12, CSI = 0.77
- _Optimal 4____8-km bulk shear = 10 m s_-1
- 	POD = 0.83, FAR = 0.26, CSI = 0.64
- _Optimal 0____3-km SRH = 200 m__2__ s_-2
- 	POD = 0.60, FAR = 0.38, CSI = 0.44

## 10 km

**10 km**

**10 km**

## Thermodynamic Results:

- _Long-Lived Supercells_
- 	MLCAPE = 1415 J kg-1  643
- 	MLCIN = -42 J kg-1  53
- 	MLBRN = 13  8
- 	MLLCL = 1448 m  502
- _Short-Lived Supercells_
- 	MLCAPE = 1623 J kg-1  1241
- 	MLCIN = -68  J kg-1  69
- 	MLBRN = 31  46
- 	MLLCL = 1771 m  565

## Large-Scale Environments:

- Long-lived supercells often moved parallel to a moisture or instability axis, or *moved at a similar speed* as an instability axis
- Supercells were *not* observed to re-orient themselves along boundaries (change direction), but they often occurred in close proximity to them...e.g., the BIS case

## One Possible Setting:

**L**

- SC motion

- 08-km bulk shear > 25-30 m s-1
- 8-km SR wind > 13-15 m s-1
- MLCAPE > 800-1000 J kg-1
- MLCIN < 75-100 J kg-1
- MLBRN = 10 to 25
- MLLCL < 1500-2000 m

- sfc

- 8 km

## One Possible Setting:

**L**

- SC motion

- 08-km bulk shear > 25-30 m s-1 (22)
- 8-km SR wind > 13-15 m s-1 (6)
- MLCAPE > 800-1000 J kg-1 (2483)
- MLCIN < 75-100 J kg-1 (8.9)
- MLBRN = 10 to 25 (12)
- MLLCL < 1500-2000 m (1167)

- sfc

- 8 km

- BIS values
- from earlier
- radar example

## Summary:

- Long-lived supercells ( 4 h):
- typically occur in *strong shear environments*, with *strong storm-relative upper-level flow*
- typically relatively “isolated” (vs. short-lived)
- produce considerable severe weather
- Supercell motion and boundary *orientation* may play a key role in supercell longevity
- External factors may act to limit supercell longevity in an otherwise favorable setting

## Acknowledgments:

- The COMET Program
- The NOAA Central Library
- Wendy Abshire, COMET
- Dave Carpenter, NWS RAP
- Charlie Knight, NCAR
- Steve Williams, NCAR

## Additional Information:

- 21st Conference on SLS, 655-658.
- matthew.bunkers@noaa.gov
- Thank you for your attention—time for questions.