afh15-101 ch 3 p. 181-202

Thunderstorm-produced severe weather includes tornadoes, hail, strong winds, lightning, and heavy rainfall.
Types of Thunderstorms:
- Single Cell
- Multi-Cell
- Supercell
Factors determining thunderstorms:
- Vertical motions and instability of an air mass (primary factors).
- Wind shear influences the type and sustenance of thunderstorms.
Hodograph patterns visually depict wind shear and help identify storm types.

Characteristics:
- Short-lived (30-60 minutes) with one rapid updraft.
- Precipitation begins at the mature stage, supported by a single downdraft.
- Weak vertical and horizontal wind shears; random shear profile on the hodograph.
- Motion aligns with the mean wind in the lowest 5-7 km of the atmosphere.
Severe weather is rare but possible in stronger cells (e.g., high winds, small hail).

Description:
- Clusters of short-lived single-cell storms.
- Each cell generates cold outflows, forming gust fronts where new cells develop every 5-15 minutes.
Characteristics:
- Straight-line shear profiles; strong directional and speed shear.
- Individual cells move with gust front and mean wind direction.
Potential severe weather:
- Flash flooding, large hail, weak tornadoes near updraft centers.

Structure:
- Contains 3 main components: rotating updraft, forward-flanking downdraft, and rear-flanking downdraft.
Characteristics:
- Can last several hours; frequent producers of severe weather.
- Curved shear profile in lower levels, straight-line above 3 km.
- Contains significant directional shear in the first 3 km of the atmosphere.
Types of Supercells:
- Classic Supercell: Isolated, capable of producing large hail, strong winds, and tornadoes. Identified by the "hook echo" pattern.
- High Precipitation (HP) Supercell: Develops in moist layers and produces heavier rain. Radar patterns vary and can evolve into bow configurations.
- Low Precipitation (LP) Supercell: Smaller precipitation amounts but capable of severe weather; appears benign on radar.

Definition: Strong, localized downdrafts resulting in damaging surface winds (50 knots or greater).
Types:
- Dry Microburst: No significant rainfall, originates from high-based clouds.
- Wet Microburst: From rainy cells, significant amounts of precipitation.
- Hybrid Microburst: Combination characteristics of dry and wet.

Straight-line wind events that develop from severe convective storms.
Types:
- First type: Rapidly propagating segment of squall line, often linked to a strong low-pressure system.
- Second type: Develops in weak frontal systems featuring moisture-rich environments.

Downdraft Convective Available Potential Energy (DCAPE): Measures energy available for air descent; essential for strong downdraft predictions.
Factors affecting DCAPE:
- Instability via warm advection, moisture advection, and cold air advection.
Low and Mid-Level Moisture Profile:
- Conditions promoting convective winds involve moist low-levels and dry mid-levels.
Low-level Vertical Wind Shear (VWS): Enhances potential of downdrafts reaching the surface.
Low-level lapse rates: Steep lapse rates favor convective winds and are optimal for downdraft maintenance.
Height of Minimum Wet Bulb Potential Temperature Aloft: Determines where downdrafts originate, affecting their strength.

Mid-Level Lapse Rates: Critical for hail formation; must be steep (greater than 6°C km-1).
Wet Bulb Zero (WBZ) Height: Indicates potential hail growth heights; ideal WBZ heights are between 5000 and 11000 feet AGL.
Mid-Level Moisture Profile: Dry air aloft favors severe hail growth.
Convective Instability: High CAPE values increase severe hail potential.

Precipitable Water (PW): Higher PW increases heavy rainfall potential; values above 1 inch favor heavy rain.
Relative Humidity in the Lowest 200 mb: High RH improves precipitation efficiency; 70% or more is optimal.
Surface Dew Points: Higher dew points indicate more moisture available for precipitation.
Moisture Convergence: Increases local lifting and precipitation likelihood.
K Index: High values (greater than 25) indicate strong potential for heavy rainfall.

K Index and Lifted Index (LI): Assess stability and deep moisture; high values indicate potential for lightning production.
Showalter Stability Index (SSI): Values below zero indicate increased thunderstorm potential.
Convective Available Potential Energy (CAPE): Higher CAPE in specific layers increases lightning likelihood.

Wind Profiles: A veering wind profile in the lowest 3 km fosters tornado development.
0-6 km Wind Shear: Values greater than 30 knots enhance tornado potential.
Inflow Layer Wind Speeds: Warm moist inflow exceeding 15 knots strengthens updrafts.
Storm Relative Helicity (SRH): High SRH values indicate greater likelihood of generating a rotating updraft.
CAPE: Tornadoes most common with CAPE values between 1500 J kg-1 and 4000 J kg-1.
Convective Inhibition (CIN): Weak Capping allows storm energy release leading to tornado development.

Monitoring synoptic patterns helps predict severe weather potential in mid-latitudes.
Type A (Dryline): Characterized by rapid thunderstorm formation along moisture gradients.
Type B (Frontal): Associated with prefrontal squall lines where cold fronts collide with warm, moist air.
Type C (Overrunning): Severe weather due to warm, moist air overrunning cold air masses.
Type D (Cold Core): Defined by cold core lows; can produce funnel clouds and occasional tornadoes.
Type E (Squall Line): Well-defined squall lines leading to rapid thunderstorm development.

Stability Indices: Various indices help assess thunderstorm potential, but should not be the sole basis for forecasts.
Key indices include CAPE and Bulk Richardson Number (BRN), which provide insights into storm types and severity.