5.3 Severe Weather
Severe weather includes thunderstorms, tornadoes, and damaging winds. These phenomena require specific atmospheric conditions: instability, moisture, lift, and wind shear.
Thunderstorm Types
Single Cell
Brief, weak, low shear environment. ~30 min lifetime.
Multicell
Cluster of cells in various stages. Moderate wind shear.
Supercell
Rotating updraft (mesocyclone). Produces most tornadoes. High shear + CAPE.
Tornadoes
| EF Scale | Wind (mph) | Damage |
|---|---|---|
| EF0 | 65-85 | Light |
| EF1 | 86-110 | Moderate |
| EF2 | 111-135 | Considerable |
| EF3 | 136-165 | Severe |
| EF4 | 166-200 | Devastating |
| EF5 | >200 | Incredible |
Python: Severe Weather Parameters
#!/usr/bin/env python3
"""severe_weather.py - Severe weather indices"""
import numpy as np
def significant_tornado_parameter(CAPE, SRH, shear_0_6km, LCL):
"""STP for tornado forecasting"""
CAPE_term = CAPE / 1500
SRH_term = SRH / 150
shear_term = shear_0_6km / 20
LCL_term = (2000 - LCL) / 1000 if LCL < 2000 else 0
return CAPE_term * SRH_term * shear_term * max(LCL_term, 0)
# Example: moderate severe weather setup
CAPE = 2500 # J/kg
SRH = 200 # m²/s² (storm-relative helicity)
shear = 25 # m/s (0-6 km bulk shear)
LCL = 1000 # m
stp = significant_tornado_parameter(CAPE, SRH, shear, LCL)
print(f"Significant Tornado Parameter: {stp:.2f}")
print(f"Interpretation: {'High tornado risk' if stp > 1 else 'Marginal'}")