radar – supercell convection conceptual models
DESCRIPTION
Radar – Supercell Convection Conceptual Models. Supercells. Well developed Supercell with Rear Anvil. MAMMATUS CLOUDS (in the overhanging anvil). MAMMATUS. HEAVY RAIN. RAIN. HAIL. SHORT FLANKING TOWERS (no rain). RAIN FREE BASE. OVERSHOOTING TOPS. Banding. Wall Cloud. Tail Cloud. - PowerPoint PPT PresentationTRANSCRIPT
Analysis & Diagnosis 1Radar Palette Home Supercell Convection
Radar – Supercell Convection Conceptual Models
Analysis & Diagnosis 2Radar Palette Home Supercell Convection
Supercells
Analysis & Diagnosis 3Radar Palette Home Supercell Convection
Radar Palette Home Supercell Convection
Well developed Supercell with Rear Anvil
Radar Palette Home Supercell Convection
MAMMATUS CLOUDS (in the overhanging anvil)
Radar Palette Home Supercell Convection
RAINRAIN
HEAVYHEAVY RAINRAIN
HAILHAIL
RAIN FREE BASERAIN FREE BASE
SHORT FLANKING TOWERS (no rain)
OVERSHOOTING OVERSHOOTING TOPSTOPS
MAMMATUSMAMMATUS
Radar Palette Home Supercell Convection
Banding
Radar Palette Home Supercell Convection
Wall Cloud
Tail Cloud
Radar Palette Home Supercell Convection
Radar Palette Home Supercell Convection
Supercell Identification
• Cloud Features
Radar Palette Home Supercell Convection
LP Supercell
• Less common supercell
Radar Palette Home Supercell Convection
HP Supercell
• More common supercell
Radar Palette Home Supercell Convection
Supercell Modeling - Satellite Features - Low Level Flow Boundaries• Outflow boundary interaction...
Radar Palette Home Supercell Convection
Supercell Modeling - Satellite FeaturesMid Level Flows relating to Low Level Flows• V- notch and other flows...
Radar Palette Home Supercell Convection
Storm Propagation
• Regeneration• Propagation• Train-echo systems
Radar Palette Home Supercell Convection
Supercell Splitting - One
• Storm splitting in straight line shear
Radar Palette Home Supercell Convection
Supercell Splitting - Two
• Low level baroclinicity increases mid level meso
Radar Palette Home Supercell Convection
Supercell Splitting - Three
• Veering hodo favours the right mover...
Radar Palette Home Supercell Convection
Supercell Splitting - Four
• straight line shear• cyclonic shear with height
Radar Palette Home Supercell Convection
Supercell Structure
• Potential satellite and radar clues to a supercell
Analysis & Diagnosis 21Radar Palette Home Supercell Convection
Supercell Prediction
Analysis & Diagnosis 22Radar Palette Home Supercell Convection
Instability
• Thermodynamic parameters• The most important include: • CAPE• LI• Cap• Dewpoint depression 700 through 500 mb
Analysis & Diagnosis 23Radar Palette Home Supercell Convection
Moisture - Dewpoints
• Greater than 24C (75F) Incredibly juicy• 18-23C (65-74F) Juicy• 12-17C (55-64F) Semi-juicy• Less than 11C (55F) Low moisture content
Analysis & Diagnosis 24Radar Palette Home Supercell Convection
Conceptual Model for Supercell Tornadogenesis
Analysis & Diagnosis 25Radar Palette Home Supercell Convection
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 • 9+ very large
Analysis & Diagnosis 26Radar Palette Home Supercell Convection
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.
Analysis & Diagnosis 27Radar Palette Home Supercell Convection
Cell Splitting
Analysis & Diagnosis 28Radar Palette Home Supercell Convection
0-3km VWS
• Directional Shear• Cause horizontal vorticity • Also produces differential advection• Best case… SE at sfc… SW at 700 mb
Analysis & Diagnosis 29Radar Palette Home Supercell Convection
Right Propagating Supercells
Analysis & Diagnosis 30Radar Palette Home Supercell Convection
Tornadogenesis and the RFD
Analysis & Diagnosis 31Radar Palette Home Supercell Convection
Storm-Relative 500 mb Winds
• 500 mb level) storm-relative (S-R) winds useful to help differentiate between tornadic and non-tornadic supercells within the overall environment
• Balance between Low-Level Inflow and• Low-level Rear Flank Downdraft
Analysis & Diagnosis 32Radar Palette Home Supercell Convection
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.
Analysis & Diagnosis 33Radar Palette Home Supercell Convection
Vorticity Generation
• Advection + Tilting + Stretching• Stretching term is the ONLY term capable of
amplifying vorticity to tornadic magnitudes
Analysis & Diagnosis 34Radar Palette Home Supercell Convection
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.
Analysis & Diagnosis 35Radar Palette Home Supercell Convection
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
Analysis & Diagnosis 36Radar Palette Home Supercell Convection
Upper level Jet Stream
• Greater 200 knots Incredible divergence• 150 to 200 knots Large divergence• 100 to 149 knots Good divergence• 70 to 99 knots Marginal divergence• Less 70 knots Small divergence
Analysis & Diagnosis 37Radar Palette Home Supercell Convection
Lake Breeze Boundaries – Guelph Tornado
Analysis & Diagnosis 38Radar Palette Home Supercell Convection
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
Analysis & Diagnosis 39Radar Palette Home Supercell Convection
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.
Analysis & Diagnosis 40Radar Palette Home Supercell Convection
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
Analysis & Diagnosis 41Radar Palette Home Supercell Convection
CAP
• Cap strength in degrees Celsius• Cap needs to be less than 2 in general before it
can be broken
Analysis & Diagnosis 42Radar Palette Home Supercell Convection
Mesocyclone and the Updraft
Analysis & Diagnosis 43Radar Palette Home Supercell Convection
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.
Analysis & Diagnosis 44Radar Palette Home Supercell Convection
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.
Analysis & Diagnosis 45Radar Palette Home Supercell Convection
Cyclic Mesocyclones
Analysis & Diagnosis 46Radar Palette Home Supercell Convection
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
Analysis & Diagnosis 47Radar Palette Home Supercell Convection
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
Analysis & Diagnosis 48Radar Palette Home Supercell Convection
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
Analysis & Diagnosis 49Radar Palette Home Supercell Convection
Horizontal Convective Rolls
• Align with the mean wind• Forced by surface heating• Identified by cloud streets• Contribute to convection initiation
Analysis & Diagnosis 50Radar Palette Home Supercell Convection
Horizontal Roll Conceptual Model
Analysis & Diagnosis 51Radar Palette Home Supercell Convection
Analysis & Diagnosis 52Radar Palette Home Supercell Convection
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
Analysis & Diagnosis 53Radar Palette Home Supercell Convection
Torndogenesis Failure
• 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
Analysis & Diagnosis 54Radar Palette Home Supercell Convection
Nowcasting Tornado Potential
• 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
Analysis & Diagnosis 55Radar Palette Home Supercell Convection
Improving Warnings for Areas with No Radar
• Weather Watcher Coverage• Anticipation based on Diagnosis• Upstream Warnings/Prior Events• Satellite/Surface Observations
– Enhanced-V notch– Boundaries– Destabilization