Radar – Supercell Convection Conceptual Models
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Supercell Convection
Analysis & Diagnosis 1
Supercells
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Supercell Convection
Analysis & Diagnosis 2
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Supercell Convection
Analysis & Diagnosis 3
Well developed Supercell with Rear Anvil
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Supercell Convection
MAMMATUS CLOUDS
(in the overhanging anvil)
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Supercell Convection
MAMMATUS
OVERSHOOTING
TOPS
HEAVY
RAIN
HAIL
SHORT FLANKING
TOWERS (no rain)
RAIN FREE BASE
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Supercell Convection
RAIN
Banding
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Supercell Convection
Wall Cloud
Tail Cloud
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Supercell Convection
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Supercell Convection
Supercell Identification
• Cloud Features
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Supercell Convection
LP Supercell
• Less common
supercell
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Supercell Convection
HP Supercell
• More common
supercell
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Supercell Convection
Supercell Modeling - Satellite Features Low Level Flow Boundaries
• Outflow boundary interaction...
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Supercell Convection
Supercell Modeling - Satellite Features
Mid Level Flows relating to Low Level Flows
• V- notch and other flows...
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Supercell Convection
Storm Propagation
• Regeneration
• Propagation
• Train-echo systems
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Supercell Convection
Supercell Splitting - One
• Storm splitting in straight line shear
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Supercell Convection
Supercell Splitting - Two
• Low level baroclinicity increases mid level meso
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Supercell Convection
Supercell Splitting - Three
• Veering hodo
favours the right
mover...
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Supercell Convection
Supercell Splitting - Four
• straight line shear
• cyclonic shear with height
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Supercell Convection
Supercell Structure
• Potential
satellite and
radar clues to a
supercell
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Supercell Convection
Supercell Prediction
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Supercell Convection
Analysis & Diagnosis 21
Instability
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Thermodynamic parameters
The most important include:
CAPE
LI
Cap
Dewpoint depression 700 through 500 mb
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Supercell Convection
Analysis & Diagnosis 22
Moisture - Dewpoints
• Greater than 24C (75F) Incredibly juicy
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18-23C (65-74F)
Juicy
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12-17C (55-64F)
Semi-juicy
• Less than 11C (55F) Low moisture content
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Supercell Convection
Analysis & Diagnosis 23
Conceptual Model for Supercell
Tornadogenesis
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Supercell Convection
Analysis & Diagnosis 24
Shear
• Positive shear in the 0 to 3km above ground
level. Units are in time to the negative 1.
• 0 to 3 weak
• 4 to 5 moderate
• 6 to 8 large
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9+ very large
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Supercell Convection
Analysis & Diagnosis 25
Speed Shear
• Causes updrafts to tilt in the vertical thus leading
to supercell storms.
• Speed shear also causes tubes of horizontal
vorticity, which can be ingested into
thunderstorms.
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Supercell Convection
Analysis & Diagnosis 26
Cell Splitting
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Supercell Convection
Analysis & Diagnosis 27
0-3km VWS
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Directional Shear
Cause horizontal vorticity
Also produces differential advection
Best case… SE at sfc… SW at 700 mb
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Supercell Convection
Analysis & Diagnosis 28
Right Propagating Supercells
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Supercell Convection
Analysis & Diagnosis 29
Tornadogenesis and the RFD
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Supercell Convection
Analysis & Diagnosis 30
Storm-Relative 500 mb Winds
• 500 mb level) storm-relative (S-R) winds useful
to help differentiate between tornadic and nontornadic supercells within the overall
environment
• Balance between Low-Level Inflow and
• Low-level Rear Flank Downdraft
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Supercell Convection
Analysis & Diagnosis 31
Storm-Relative 500 mb Winds
• 500 mb S-R winds = 16 kts (8 m/s)
Lower limit for tornadic supercells.
• 500 mb S-R winds = 40 kts (20 m/s)
Aprx upper limit for tornadic supercells.
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Supercell Convection
Analysis & Diagnosis 32
Vorticity Generation
• Advection + Tilting + Stretching
• Stretching term is the ONLY term capable of
amplifying vorticity to tornadic magnitudes
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Supercell Convection
Analysis & Diagnosis 33
500 millibar vorticity
• Vorticity is a function of curvature, earth vorticity,
and speed gradients.
• If the values of vorticity are being rapidly
advected, divergence will "in the real world" be
much more than if the winds through the
vorticity maximum are stationary or moving
slowly.
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Supercell Convection
Analysis & Diagnosis 34
Low Level Jet - LLJ
• Strong low level winds will quickly advect warm
and moist air into a region if it is associated with
the low level jet
• Low level convergence along LLJ
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Supercell Convection
Analysis & Diagnosis 35
Upper level Jet Stream
• Greater 200 knots Incredible divergence
• 150 to 200 knots Large divergence
• 100 to 149 knots Good divergence
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70 to 99 knots Marginal divergence
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Less 70 knots Small divergence
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Supercell Convection
Analysis & Diagnosis 36
Lake Breeze Boundaries – Guelph Tornado
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Supercell Convection
Analysis & Diagnosis 37
Maximum Updraft Speed
• W-max = square root of [2(CAPE)]
• CAPE of 1500-2500 J/kg gives a w-max range of
about 50-70 m/s (100-140 kts).
• due to water loading, mixing, entrainment, and
evaporative cooling, the actual w-max is
approximately one-half that calculated
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Supercell Convection
Analysis & Diagnosis 38
CAPE Distribution
• A longer, narrower profile represents the
potential for a slower updraft acceleration but
taller thunderstorms which is best for high
precipitation efficiency
• A shorter, fatter profile would lead to a more
rapid vertical acceleration which would be
important for potential development of updraft
rotation within the storm.
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Supercell Convection
Analysis & Diagnosis 39
Convective Inhibition - CINH
• negative area on a sounding. A large cap or a
dry planetary boundary layer will lead to high
values of CINH and stability
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Supercell Convection
Analysis & Diagnosis 40
CAP
• Cap strength in degrees Celsius
• Cap needs to be less than 2 in general before it
can be broken
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Supercell Convection
Analysis & Diagnosis 41
Mesocyclone and the Updraft
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Supercell Convection
Analysis & Diagnosis 42
RFD
• If RFD is too cold and strong then the updraft
may be undercut before tornadogenesis can
begin
• If the RFD is relatively warm, the tornadoes can
be long lived and violent.
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Supercell Convection
Analysis & Diagnosis 43
Precipitation Drag RFD’s
• In moist thermodynamic profiles, evaporative
cooling potential minimal even if heavy PCPN is
close to the updraft… precipitation drag may drive
the RFD.
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Supercell Convection
Analysis & Diagnosis 44
Cyclic Mesocyclones
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Supercell Convection
Analysis & Diagnosis 45
Tornado Events
• Likely isolated supercells but can develop within line
segments
• High Ambient SRH (0-2km>200 m2s2) except when high
CAPE and deviant storm motion locally creates helicity
• Mid-upper level winds (4-6km >15kts) aid tornado
development and longevity
• CAPE/CAPE Distribution/LFC/LCL and Evaporative
cooling (RFD)
• Boundaries – local helicity and possibly lower LCL
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Supercell Convection
Analysis & Diagnosis 46
Discrete Supercells
• Convergence more localized than linear
• If CIN/CAP weak, convergence trigger can be very
subtle
• Strong CIN/CAP (50 J/kg) under strong convergence
• Shear is through a deep layer (0-6km)
• Mean Shear Vector oriented at a relatively large angle to
the initiating boundary
• Discrete Supercells can evolve into lines but rarely from
lines to discrete
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Supercell Convection
Analysis & Diagnosis 47
LFC/LCL Heights
• For greater tornado threat, relatively low LCL
heights (<6000 ft)
• High LCL heights associated with dry boundary
layers promote
– Convective downbursts
– Outflow dominated convection
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Supercell Convection
Analysis & Diagnosis 48
Horizontal Convective Rolls
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Align with the mean wind
Forced by surface heating
Identified by cloud streets
Contribute to convection initiation
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Supercell Convection
Analysis & Diagnosis 49
Horizontal Roll Conceptual Model
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Supercell Convection
Analysis & Diagnosis 50
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Supercell Convection
Analysis & Diagnosis 51
Upper Patterns
• SWLY upper flow ahead of sharp upper trof
• WSWLY upper flow associated with low
amplitude S/W trofs embedded with a
progressive WLY flow pattern
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Supercell Convection
Analysis & Diagnosis 52
Torndogenesis Failure
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LFC too high
PBL too dry
Storms evolve into lines too quickly
Too little CAPE above the LFC
Too little helicity in the absence of boundaries
Deep Layer shear too strong for the CAPE
Mid Level storm relative shear too weak
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Supercell Convection
Analysis & Diagnosis 53
Nowcasting Tornado Potential
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Monitor vertical shear (VWP data)
Jet Streaks
Surface Pressure Tendencies
Surface Analysis Boundaries
Satellite – Breaks in clouds along line
Deviant Storm Motion – Right Movers
Rapid Destabilization/ Pressure Falls
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Supercell Convection
Analysis & Diagnosis 54
Improving Warnings for Areas with No Radar
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Weather Watcher Coverage
Anticipation based on Diagnosis
Upstream Warnings/Prior Events
Satellite/Surface Observations
– Enhanced-V notch
– Boundaries
– Destabilization
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Supercell Convection
Analysis & Diagnosis 55