Jun 7, 2022 Omaha–Nebraska Hail

Hail Vulnerability Model — v1.6 Physics

Damage probability is computed using a physically grounded stone-population model. Rather than mapping peak MESH directly to a damage ratio, the model distributes stone impacts across the realistic hail size spectrum — where the largest stones are rare outliers, not the norm. A surface-occurrence correction accounts for hail that melts or evaporates before reaching the ground.

Algorithm

1. Peak MRMS MESH is corrected for radar calibration bias (Ortega 2018: 0.75×) and storm type (supercell 1.15×) to estimate the effective largest stone diameter D_l.
2. Grieser & Hill (2019) power-law fits give average stone diameter D_a, storm duration T, and hit rate Hr as functions of D_l, calibrated on 37,726 CoCoRaHS ground-truth observations.
3. Stone size distribution follows a Gamma distribution (α = 1.75; Li et al. 2024) between 5 mm and D_l.
4. Each 1mm size bin is assigned a damage probability via a lognormal fragility curve for unrated asphalt shingle (θ = 46 mm, γ = 0.25; Li et al. 2024).
5. Aggregate P_fail = 1 − ∏(1 − p_i)^N_i across all size bins. Duration exposure applied as cap-limited multiplier (max 1.4×).
6. Ackermann et al. (2024) HDE sigmoid surface-occurrence correction: P_surface = 1/(1 + e^{−0.18(MESH−27)}). Accounts for hail melting and evaporating aloft before reaching the ground. Main effect at swath edges (1.0″–1.5″ MESH).

Key Parameters

Validation Note

Published insured loss for the Jun 7, 2022 multi-state outbreak: ~$1.9B (NCEI billion-dollar catalog, all perils, all states). This model covers Nebraska roof loss only. Roof loss is estimated at 55–60% of total insured; NE is the dominant state by structure density. Model output of $145.9M reflects roof-only scope against footprint-based RCV at 2021 pricing.

References