Forecasting
Hodograph shapes guide
Every hodograph shape tells you something. Here is a field guide from straight to sickle to S-shaped, and what each means for storm mode.
The straight hodograph
A straight-line hodograph — all wind vectors point roughly the same direction with just speed changes.
- Indicates unidirectional shear.
- Storm mode: multicell, occasional splitting supercells.
- Both mirror-image left- and right-moving supercells possible.
- Tornado risk: low to moderate.
- Common in weak-shear environments.
The curved hodograph
A hodograph that curves clockwise with height — winds veer with height.
- Indicates DIRECTIONAL shear plus SPEED shear.
- Storm mode: classic right-moving supercell favored.
- Left-movers suppressed.
- Tornado risk: high if curvature is in the low levels (0-1 km).
- The classic tornado hodograph.
The counterclockwise curved hodograph
Rare. Winds back with height (turn counterclockwise).
- Rare in warm-sector setups.
- Left-moving supercells favored.
- Anticyclonic tornadoes possible.
- Southern Hemisphere: this shape is normal (mirror image).
The sickle-shaped hodograph
Curved 0-1 km, then straight above.
- Ideal for tornadoes.
- Low-level curvature = strong SRH.
- Upper straight = storm-scale organization.
- Common in significant tornado outbreaks.
The S-shaped hodograph
Curves one way in low levels, then reverses aloft.
- Complex.
- Storm mode can shift over time.
- Multicell + supercell mix common.
- Fronts / boundaries often produce this shape.
The looped hodograph
Winds return to same direction after a full 360° turn.
- Very rare.
- Extreme shear.
- Some famous tornado hodographs approach this.
- Tropical-cyclone-spawned tornadoes can produce this.
The key metrics from a hodograph
0-6 km bulk shear
Distance from tail to head of hodograph. > 40 kt = supercells favored.
0-1 km bulk shear
Low-level shear. > 15 kt supports tornadoes.
0-1 km SRH
Area swept by 0-1 km hodograph. > 200 m²/s² = tornado favored.
0-3 km SRH
Broader storm-relative helicity. > 300 m²/s² violent-tornado favored.
Storm motion
Estimated by Bunkers method: shifted from mean wind.
Effective SRH
Modern preferred measure. Uses actual inflow layer.
How to read a hodograph in the field
- Load the RAP or SPC mesoanalysis.
- Find your target zone.
- Click through to hodograph.
- Look at 0-1 km curvature: strong curl = tornado potential.
- Look at 6 km end: strong shear = supercell.
- Look at storm motion arrow: which direction storms go.
- Look at cross-section of hodograph vs environment: is storm INSIDE the strongest inflow?
The famous tornado hodographs
1974 Super Outbreak
Long, sharply curved low-level hodograph. Massive shear.
1999 Bridge Creek-Moore
Sickle shape. Textbook tornado shape.
2011 April 27 Super Outbreak
Extreme 0-1 km shear. Long-lived tornado hodograph.
2013 Moore
Similar signature to 1999.
2013 El Reno
Extreme total shear. Massive SRH.
The composite indices
- STP (Significant Tornado Parameter) — combines SRH, CAPE, LCL, shear. Values > 3 = high tornado risk.
- SCP (Supercell Composite Parameter) — supercell risk index.
- EHI (Energy Helicity Index) — SRH × CAPE / 160,000. Values > 2 favorable.
- None replaces reading the actual hodograph.