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Convective Storm types Convective Storm types James LaDue James LaDue FMI Severe Storms Workshop FMI Severe Storms Workshop June 2005 June 2005

Convective Storm types

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Convective Storm types. James LaDue FMI Severe Storms Workshop June 2005. Outline. Single cell convection Ordinary cell convection Sheared cell convection Multicell convection. Fundamental Concepts of Convection. Ordinary cell convection. Dominate when the vertical shear is small - PowerPoint PPT Presentation

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Page 1: Convective Storm types

Convective Storm typesConvective Storm typesConvective Storm typesConvective Storm types

James LaDueJames LaDue

FMI Severe Storms WorkshopFMI Severe Storms Workshop

June 2005June 2005

James LaDueJames LaDue

FMI Severe Storms WorkshopFMI Severe Storms Workshop

June 2005June 2005

Page 2: Convective Storm types

OutlineOutlineOutlineOutline

• Single cell convectionSingle cell convection– Ordinary cell convectionOrdinary cell convection– Sheared cell convectionSheared cell convection

• Multicell convectionMulticell convection

Page 3: Convective Storm types

Fundamental Concepts of Fundamental Concepts of ConvectionConvection

Fundamental Concepts of Fundamental Concepts of ConvectionConvection

Page 4: Convective Storm types

Ordinary cell convectionOrdinary cell convectionOrdinary cell convectionOrdinary cell convection

• Dominate when the Dominate when the vertical shear is smallvertical shear is small

• Dominated by Dominated by buoyancy processesbuoyancy processes

Mogollon Rim, AZ1999 James LaDue

Page 5: Convective Storm types

Ordinary cell evolutionOrdinary cell evolutionOrdinary cell evolutionOrdinary cell evolution

TCU + 7 min

-10° C

Page 6: Convective Storm types

Ordinary cell evolutionOrdinary cell evolutionOrdinary cell evolutionOrdinary cell evolution

TCU + 14 min

-10° C

Page 7: Convective Storm types

Ordinary cell evolutionOrdinary cell evolutionOrdinary cell evolutionOrdinary cell evolution

TCU + 21 min

-10° C

Page 8: Convective Storm types

Ordinary cell evolutionOrdinary cell evolutionOrdinary cell evolutionOrdinary cell evolution

TCU + 28 min

-10° C

Page 9: Convective Storm types

Pulse storm downburstsPulse storm downburstsPulse storm downburstsPulse storm downbursts

TCU + 35 min

-10° C

Page 10: Convective Storm types

Radar and visual view of an Radar and visual view of an ordinary cell thunderstormordinary cell thunderstormRadar and visual view of an Radar and visual view of an ordinary cell thunderstormordinary cell thunderstorm

• Look for onset of Look for onset of elevated reflectivity elevated reflectivity core as the updraft core as the updraft reaches the freezing reaches the freezing levellevel

• Note the time when the Note the time when the intense reflectivity intense reflectivity reaches groundreaches ground

• Note the time of Note the time of dissipation dissipation

Link to loop

Page 11: Convective Storm types

What CAPE is the storm realizing?What CAPE is the storm realizing?What CAPE is the storm realizing?What CAPE is the storm realizing?

CAPE = 1490 J/kgWmax = (2CAPE)1/2

= 54 m/sAssume 50% or 27 m/sEL temp = -60 C

But does this storm appear to have a 27 m/s updraft and an EL = -60 C?

Page 12: Convective Storm types

What CAPE is the storm realizing?What CAPE is the storm realizing?What CAPE is the storm realizing?What CAPE is the storm realizing?

A more realistic parcel path is more like the new curve Causes?•Dry air entrainment •Lower initial parcel e

Page 13: Convective Storm types

Influence of CAPE profilesInfluence of CAPE profilesInfluence of CAPE profilesInfluence of CAPE profiles

• Which sounding Which sounding is most likely to is most likely to produce a produce a stronger updraft?stronger updraft?

• Sounding ASounding A– Stronger initial Stronger initial

accelerationacceleration– Less Less

precipitation dragprecipitation dragCAPE (A) = CAPE (B)

Page 14: Convective Storm types

Influence of CAPE profilesInfluence of CAPE profilesInfluence of CAPE profilesInfluence of CAPE profiles

• CAPE density = CAPE/depth CAPE density = CAPE/depth – When high, expect rapid upward parcel accelerationWhen high, expect rapid upward parcel acceleration– Occurs with steep lapse rates above and below the LFCOccurs with steep lapse rates above and below the LFC

Page 15: Convective Storm types

Influence of CAPE profilesInfluence of CAPE profilesInfluence of CAPE profilesInfluence of CAPE profiles

• Two temperature profiles Two temperature profiles with the same moisture.with the same moisture.

• Both yield 800 j/kg of CAPEBoth yield 800 j/kg of CAPE

• Lowering the Lowering the maximum buoyancy maximum buoyancy level increases updraft level increases updraft strength at low levels.strength at low levels.

Zb = 5.5 km

Zb = 2.5 kmAfter McCaul and Weisman 2000 - MWR

Page 16: Convective Storm types

DowndraftsDowndraftsDowndraftsDowndrafts

• Commonly initiate in Commonly initiate in the 3 – 5 km AGL the 3 – 5 km AGL layerlayer

• Initiated by Initiated by precipitation loadingprecipitation loading

• Evaporational Evaporational cooling adds cooling adds significant significant contributioncontribution

Precipitation loading becomes strong with reflectivity > 55 dBZ

Page 17: Convective Storm types

Downdraft buoyancyDowndraft buoyancyDowndraft buoyancyDowndraft buoyancy

• From evaporational From evaporational coolingcooling

• Measured by Measured by Downdraft CAPE Downdraft CAPE (DCAPE)(DCAPE)

• Similar to CAPE Similar to CAPE but in reversebut in reverse

Average w

of the downdraft

Average w of the 700-500 mb layer

w of the updraft

Downdraft initiation level

DCAPE

Page 18: Convective Storm types

Downdraft buoyancyDowndraft buoyancyDowndraft buoyancyDowndraft buoyancy

• Larger DCAPE Larger DCAPE mostly means mostly means stronger stronger downdraftsdowndrafts

• However, stronger However, stronger CAPE can result in CAPE can result in stronger stronger precipitation precipitation loadingloading

Average w

of the downdraft

Average w of the 700-500 mb layer

w of the updraft

Downdraft initiation level

DCAPE

Page 19: Convective Storm types

Downdraft buoyancyDowndraft buoyancyDowndraft buoyancyDowndraft buoyancy

• DCAPE is never DCAPE is never fully utilized by the fully utilized by the downdraftdowndraft

• Downdrafts are not Downdrafts are not saturated and do saturated and do not follow the not follow the w to to

the surfacethe surface

Average w

of the downdraft

Average w of the 700-500 mb layer

w of the updraft

Downdraft initiation level

DCAPE

DCAPE is still a good starting place to estimate downdraft strength

Page 20: Convective Storm types

Downdrafts in single cellsDowndrafts in single cellsDowndrafts in single cellsDowndrafts in single cells

• Downdraft strength Downdraft strength – amount of DCAPEamount of DCAPE– precipitation loadingprecipitation loading– Nonhydrostatic vertical pressure profilesNonhydrostatic vertical pressure profiles

Page 21: Convective Storm types

Updraft/shear interactionsUpdraft/shear interactionsUpdraft/shear interactionsUpdraft/shear interactions

Page 22: Convective Storm types

Shear interactions with updraftsShear interactions with updraftsShear interactions with updraftsShear interactions with updrafts

• Updraft tilt Updraft tilt

• Causes separation Causes separation of precipitation and of precipitation and updraftupdraft

• Precipitation Precipitation loading a lesser loading a lesser threat to integrity of threat to integrity of the updraftthe updraft

Page 23: Convective Storm types

Shear interactions with updraftsShear interactions with updraftsShear interactions with updraftsShear interactions with updrafts

• Updraft tilt is a Updraft tilt is a function of its function of its strengthstrength– Given same shear, Given same shear,

a weaker updraft a weaker updraft tilts moretilts more

• Updraft tilt also a Updraft tilt also a function of shear function of shear strengthstrength

Page 24: Convective Storm types

Origins of updraft rotation from Origins of updraft rotation from straight shearstraight shear

Origins of updraft rotation from Origins of updraft rotation from straight shearstraight shear

• Incipient updraft Incipient updraft tilts horizontal tilts horizontal vorticity vorticity

• Result is a Result is a counterrotating counterrotating twin vortex on twin vortex on either side of an either side of an updraftupdraft

Page 25: Convective Storm types

Origins of updraft rotation from Origins of updraft rotation from straight shearstraight shear

Origins of updraft rotation from Origins of updraft rotation from straight shearstraight shear

• Vortices generate Vortices generate ‘dynamic’ lows at ‘dynamic’ lows at the points of the points of maximum rotation maximum rotation (usually in (usually in midlevels)midlevels)

Page 26: Convective Storm types

Origins of updraft rotation from Origins of updraft rotation from straight shearstraight shear

Origins of updraft rotation from Origins of updraft rotation from straight shearstraight shear

• Dynamic midlevel Dynamic midlevel lows encourage new lows encourage new updraft growth within updraft growth within the rotation axis.the rotation axis.

• Updraft appears to Updraft appears to move right and left of move right and left of the shear vector.the shear vector.

• Core initiates a Core initiates a downdraft in the downdraft in the middle.middle. • Result is a rotating Result is a rotating

updraft.updraft.

Page 27: Convective Storm types

Origins of updraft rotation from Origins of updraft rotation from straight shearstraight shear

Origins of updraft rotation from Origins of updraft rotation from straight shearstraight shear

• The result is a The result is a splitting stormsplitting storm

• The left and right The left and right moving members moving members rotating in opposite rotating in opposite directions directions

Page 28: Convective Storm types

Directional shearDirectional shearDirectional shearDirectional shear

L

H

L

H

Low

High

Page 29: Convective Storm types

Directional shearDirectional shearDirectional shearDirectional shear

From COMET (1996)

Page 30: Convective Storm types

Behavior of rotating storms Behavior of rotating storms from curved shearfrom curved shear

Behavior of rotating storms Behavior of rotating storms from curved shearfrom curved shear

• Clockwise turning Clockwise turning shear with height shear with height favors the cyclonically favors the cyclonically rotating supercellrotating supercell

• Counter clockwise Counter clockwise turning shear with turning shear with height favors the height favors the anticyclonically anticyclonically rotating supercellrotating supercell

Page 31: Convective Storm types

Estimating supercell motionEstimating supercell motionEstimating supercell motionEstimating supercell motion

• The Internal Dynamics (ID) methodThe Internal Dynamics (ID) method– Plot the 0-6 km mean windPlot the 0-6 km mean wind– Draw the 0-6 km shear vectorDraw the 0-6 km shear vector– Draw a line orthogonal to the shear vector through the mean Draw a line orthogonal to the shear vector through the mean

windwind– Plot the left (right) moving storm 7.5 m/s to the left (right) of Plot the left (right) moving storm 7.5 m/s to the left (right) of

the mean wind along the orthogonal line.the mean wind along the orthogonal line.

Page 32: Convective Storm types

Estimating supercell motionEstimating supercell motionEstimating supercell motionEstimating supercell motion

• The Internal Dynamics (ID) methodThe Internal Dynamics (ID) method– Plot the 0-6 km mean windPlot the 0-6 km mean wind– Draw the 0-6 km shear vectorDraw the 0-6 km shear vector– Draw a line orthogonal to the shear vector through the mean Draw a line orthogonal to the shear vector through the mean

windwind– Plot the left (right) moving storm 7.5 m/s to the left (right) of Plot the left (right) moving storm 7.5 m/s to the left (right) of

the mean wind along the orthogonal line.the mean wind along the orthogonal line.

Page 33: Convective Storm types

Estimating supercell motionEstimating supercell motionEstimating supercell motionEstimating supercell motion

• The Internal Dynamics (ID) methodThe Internal Dynamics (ID) method– Plot the 0-6 km mean windPlot the 0-6 km mean wind– Draw the 0-6 km shear vectorDraw the 0-6 km shear vector– Draw a line orthogonal to the shear vector through the mean Draw a line orthogonal to the shear vector through the mean

windwind– Plot the left (right) moving storm 7.5 m/s to the left (right) of Plot the left (right) moving storm 7.5 m/s to the left (right) of

the mean wind along the orthogonal line.the mean wind along the orthogonal line.

Page 34: Convective Storm types

Estimating supercell motionEstimating supercell motionEstimating supercell motionEstimating supercell motion

• The Internal Dynamics (ID) methodThe Internal Dynamics (ID) method– Plot the 0-6 km mean windPlot the 0-6 km mean wind– Draw the 0-6 km shear vectorDraw the 0-6 km shear vector– Draw a line orthogonal to the shear vector through the mean Draw a line orthogonal to the shear vector through the mean

windwind– Plot the left (right) moving storm 7.5 m/s to the left (right) of Plot the left (right) moving storm 7.5 m/s to the left (right) of

the mean wind along the orthogonal line.the mean wind along the orthogonal line.

Bunkers et al. (2000)

Page 35: Convective Storm types

Other types of supercellsOther types of supercellsOther types of supercellsOther types of supercells

• High precipitationHigh precipitation

• ClassicClassic

• Low PrecipitationLow Precipitation

Page 36: Convective Storm types

LP supercellsLP supercellsLP supercellsLP supercells

• No official No official definitiondefinition

• Poorly efficient Poorly efficient precipitation precipitation producersproducers

• Generate outflows Generate outflows too weak to too weak to generate strong generate strong low level low level mesocyclonesmesocyclones

Page 37: Convective Storm types

LP supercellsLP supercellsLP supercellsLP supercells

• Tornado/wind Tornado/wind threat is smallthreat is small

• Large hail threat Large hail threat is largeis large

• Near zero fl flood Near zero fl flood threatthreat

Page 38: Convective Storm types

Classic supercellsClassic supercellsClassic supercellsClassic supercells

• No official definitionNo official definition

• More efficient More efficient precipitation precipitation producersproducers

• Generate sufficient Generate sufficient outflows to generate outflows to generate strong low level strong low level mesocyclonesmesocyclones

Page 39: Convective Storm types

Classic supercellsClassic supercellsClassic supercellsClassic supercells

• Tornado/wind Tornado/wind threat is largethreat is large

• Large hail threat Large hail threat is largeis large

• Increasing fl Increasing fl flood threat for flood threat for slow moving slow moving cellscells

Page 40: Convective Storm types

High Precipitation supercellsHigh Precipitation supercellsHigh Precipitation supercellsHigh Precipitation supercells

• No official definitionNo official definition

• Most commonMost common

• Moderate efficient Moderate efficient precipitation precipitation producersproducers

• Strong outflows Strong outflows generate strong generate strong low-level mesos but low-level mesos but mostly short-livedmostly short-lived

Page 41: Convective Storm types

HP supercellsHP supercellsHP supercellsHP supercells

• Tornado threat is Tornado threat is largelarge

• Damaging wind Damaging wind threat is largerthreat is larger

• Large hail threat Large hail threat is largeis large

• Most likely Most likely responsible for responsible for flash floodsflash floods

30 Apr 2000 – Olney, TX - J. LaDue

Page 42: Convective Storm types

HP SupercellsHP SupercellsHP SupercellsHP Supercells

Adapted from Moller et al., 1990

Page 43: Convective Storm types

Cold pool/shear interactionsCold pool/shear interactionsCold pool/shear interactionsCold pool/shear interactions

• This is most This is most significant when significant when considering multicell considering multicell behaviorbehavior– Motion, longevity, Motion, longevity,

severityseverity

Page 44: Convective Storm types

Cold pool/shear interactionsCold pool/shear interactionsCold pool/shear interactionsCold pool/shear interactions

This side is where environmental and cold pool vorticity inhibit deep lifting.

This side is where environmental and cold pool vorticity enhance deep lifting.

Based on theory by Rotunno, Klemp and Weisman, 1988 (RKW)

Page 45: Convective Storm types

Cold pool shear interactionsCold pool shear interactionsCold pool shear interactionsCold pool shear interactions

• RKW theory shows how the shear/cold RKW theory shows how the shear/cold pool interactions affect the depth of liftingpool interactions affect the depth of lifting

• Strength of surface convergence does Strength of surface convergence does not indicate depth of liftingnot indicate depth of lifting

Page 46: Convective Storm types

Cold pool shear interactionsCold pool shear interactionsCold pool shear interactionsCold pool shear interactions

• According to RKW theory, According to RKW theory, the shear component the shear component perpendicular to the perpendicular to the orientation of the line orientation of the line helps determine line helps determine line longevitylongevity

• Either of the top two Either of the top two examples have good examples have good component of shearcomponent of shear

Page 47: Convective Storm types

Other cold pool/shear Other cold pool/shear considerationsconsiderations

Other cold pool/shear Other cold pool/shear considerationsconsiderations

• RKW theory tested with idealized RKW theory tested with idealized model multicell initiationmodel multicell initiation

• Other studies such as Coniglio and Other studies such as Coniglio and Stensrud suggest shear layer deeper Stensrud suggest shear layer deeper than RKW is better for anticipating than RKW is better for anticipating long-lived multicell eventslong-lived multicell events

• Cold pool shear interactions only one Cold pool shear interactions only one factor in determining convective factor in determining convective initiation potential in multicellsinitiation potential in multicells

Page 48: Convective Storm types

Multicell MotionMulticell MotionMulticell MotionMulticell Motion

• Determined by which side of the cold pool Determined by which side of the cold pool initiates the most convectioninitiates the most convection

• Affected by Affected by 1)1) Shear-cold pool interactionsShear-cold pool interactions

2)2) Instability gradientsInstability gradients

3)3) Low-level convergence (SR sense)Low-level convergence (SR sense)

4)4) 3-D boundary interactions3-D boundary interactions

Page 49: Convective Storm types

Multicell Motion Multicell Motion Multicell Motion Multicell Motion

2)2) Instability effectsInstability effects– Can modulate Can modulate

propagation of propagation of multicells toward multicells toward areas of higher areas of higher instability instability

From Richardson (1999)

Page 50: Convective Storm types

Multicell Motion Multicell Motion Multicell Motion Multicell Motion

3)3) Low-level convergence effectsLow-level convergence effectsUse original MBE Vector (“Corfidi”) Technique Use original MBE Vector (“Corfidi”) Technique

Vcl

Vprop = -VLLJ

VMBE

After Corfidi et al. (1996)

To see where low-level convergence is located, and help predict system motion

Page 51: Convective Storm types

Multicell MotionMulticell MotionMulticell MotionMulticell Motion

4)4) Boundary interactionsBoundary interactions• Modulates/enhances development of new Modulates/enhances development of new

convectionconvection

Blue = steering layer flowGreen=triple pt motionRed = multicell motion(Weaver, 1979)

Page 52: Convective Storm types

The Rear Inflow JetThe Rear Inflow JetThe Rear Inflow JetThe Rear Inflow Jet

Squall lines w/ nondescending Rear Inflow Jets (RIJs) live longer, but also consider deep-layered

shear .

Note the vorticity induced by the nondescending RIJ can counteract that of the cold pool

Page 53: Convective Storm types

Dynamics of a RIJDynamics of a RIJDynamics of a RIJDynamics of a RIJ

• Strength of RIJ Strength of RIJ depends on CAPE depends on CAPE (incr. temp excess) (incr. temp excess) and Shear (erect and Shear (erect updraft with more updraft with more direct heat into direct heat into anvil)anvil)

Page 54: Convective Storm types

Three classes of multicellsThree classes of multicellsThree classes of multicellsThree classes of multicells

SR line-parallel wind comp.

SR line-perpendicular comp.

Spe

ed

After Parker and Johnson (2000)

Page 55: Convective Storm types

Bow echoesBow echoesBow echoesBow echoes

• Bowing structure Bowing structure accompanying accompanying severe wind severe wind eventsevents

• Often has similar Often has similar hodographs to hodographs to that of that of supercellssupercells

Page 56: Convective Storm types

SRH vs shear as a supercell SRH vs shear as a supercell forecasting toolforecasting tool

SRH vs shear as a supercell SRH vs shear as a supercell forecasting toolforecasting tool

• Shear can be used Shear can be used without knowing storm without knowing storm motionmotion

• Once storm motion is Once storm motion is known, use SRH to known, use SRH to estimate supercell estimate supercell strengthstrength

60 km

Vr

C

Page 57: Convective Storm types

SummarySummarySummarySummary

• Buoyancy considerationsBuoyancy considerations– Convective Available Potential Energy (CAPE)Convective Available Potential Energy (CAPE)– Low vs. high CAPE density can alter updraft Low vs. high CAPE density can alter updraft

speed by changing precipitation loadingspeed by changing precipitation loading– Different buoyancy profiles can alter strength of Different buoyancy profiles can alter strength of

low-level updraft even though CAPE is the samelow-level updraft even though CAPE is the same– Downdraft CAPE, or DCAPE is a measure of Downdraft CAPE, or DCAPE is a measure of

downdraft strength potential but does not include downdraft strength potential but does not include precipitation loadingprecipitation loading

Page 58: Convective Storm types

SummarySummarySummarySummary

• Updraft/Shear considerationsUpdraft/Shear considerations– Causes updrafts to tilt lessoning precipitation Causes updrafts to tilt lessoning precipitation

loadingloading– Results in updraft rotationResults in updraft rotation– Straight shear results in counterrotating Straight shear results in counterrotating

supercellssupercells– Clockwise (counterclockwise) curved shear Clockwise (counterclockwise) curved shear

enhances the cyclonically (anticyclonically) enhances the cyclonically (anticyclonically) rotating supercellrotating supercell

Page 59: Convective Storm types

SummarySummarySummarySummary

• Cold pool/Shear considerationsCold pool/Shear considerations– Results in updraft rotationResults in updraft rotation– Straight shear results in counterrotating Straight shear results in counterrotating

supercellssupercells– Clockwise (counterclockwise) curved shear Clockwise (counterclockwise) curved shear

enhances the cyclonically (anticyclonically) enhances the cyclonically (anticyclonically) rotating supercellrotating supercell