✔ Surface-based CAPE > 1500 J/kg
✔ 0–1 km SRH > 150 m²/s²
✔ STP > 1
✔ LCL Height < 1000 m
✔ Strong low-level jet
✔ Surface boundary (e.g., dryline, outflow)
✔ Strong low-level convergence

(Radar-based)
1. Low-Level Rotation
Base Velocity (BV) or Storm-Relative Velocity (SRV):

Look for tight couplets of inbound and outbound velocities.

Stronger signal if this is observed close to the ground (~0.5° tilt).

2. Gate-to-Gate Shear
Found when inbound and outbound velocities are adjacent.

Often a precursor to tornadogenesis.

3. Normalized Rotation (NROT)
Product that highlights rotation strength normalized by distance.

Values above 1.0 are significant, above 2.5 are extreme.

Best used in combination with SRV.

💨 Supporting Velocity/Reflectivity Features
4. Tornado Debris Signature (TDS)
Confirmed tornado indicator when debris is lofted.

Needs:

Low Correlation Coefficient (CC) < 0.85

High Reflectivity (BR) > 35–40 dBZ

Low Differential Reflectivity (ZDR) < 0

Usually occurs alongside strong rotation.

5. Hook Echo
Seen in Base Reflectivity (BR).

Hook-shaped pattern in supercells often near the inflow notch.

6. Debris Ball
Localized high reflectivity blob (often > 55 dBZ) within the hook.

Often co-located with low CC and high NROT.

PTDS (Probability of Tornado Debris Signature)
Combines multiple parameters: BR, CC, ZDR, NROT, SW, PHI.

📌 Key Conditions to Check
Ingredient Ideal Indicator
BV / SRV Tight couplet near radar
NROT >1.0 is notable, >2.5 is extreme
CC < 0.85 indicates debris
ZDR Near 0 or negative with debris
BR Hook echo or debris ball (>50–55 dBZ)
TDS Confirmed debris via CC + BR + ZDR
PTDS >95% = strong detection
GR-MDA Persistent stacked rotation

🛰️ 1. Load Full Radar Volume
Ensure you’re viewing a complete Level II volume.

Recommended  Base Reflectivity (BR) or Storm-Relative Velocity (SRV).

📍 2. Identify Suspicious Area
Use SRV or BV at lowest tilt (0.5°) to spot a velocity couplet or rotational shear. Confirm in NROT for tight and strong rotation. Look for a hook echo or debris ball in BR.

3. Enter Cross-Section Mode
On the main toolbar, click the “Cross-Section” tool (ruler icon with a curved arrow). Your cursor will change to cross-section placement mode.

4. Draw the Cross-Section Line
Click once at the inflow side of the storm (ahead of hook). Drag to the rear-flank downdraft or rotation center. Double-click or right-click to finish the line.

5. Analyze Cross-Section Panel
You’ll now see a vertical slice of radar data:

What to Look for in a 3d volume:

SRV Gate-to-gate shear extending upward (tilted meso)
NROT Vertically stacked, persistent high values
BR Hook echo depth, debris ball reflectivity core
ZDR Collapse near debris zone
CC Vertical debris column – low CC values extending from surface upward
PTDS High probability zones aligned with debris column
If you see a narrow vertical column of low CC with strong NROT and BR > 55 dBZ at the base: confirmed TDS.