Bow Echoes & Derechoes

Bow Echoes – warm season pattern
-Quasi-stationary low-level thermal boundary oriented nearly parallel to the mean tropospheric flow
-Mid/upper-level flow is usually west or northwest, at significant angle to low-level flow. Mid-level wind speeds are usually no greater than around 40 kts
-0-2.5 km bulk wind shear is between 35-50 kts
-700-500 mb Mean RH between 50-80 pct
-CAPE is very high, averaging around 4500 J/Kg along boundary with moisture pooling

Bow Echoes – dynamic, cool season pattern
-Strong migrating shortwave trough and surface low pressure system

-Low-level jet is more parallel to mid/upper-level jet. Mid-level winds are stronger for dynamic bow echo patterns compared to warm season pattern, and instability can range from low to high. This can result in classic leading line-training stratiform QLCS, with mesovortices embedded along leading line

-700-500 mb mean RH between 50-80 pct
-Moderate to strong low-level (0-3 km) shear, with moderate to strong winds aloft, but little additional shear aloft

Derechoes
-Prolonged bow echo/damaging wind events; favored in environments with high to extreme instability; fast low to mid-level unidirectional flow
-0-3 km bulk shear > 30 kts; 0-6 km bulk shear > 40 kts

a

Development of Convective Cold Pools
-MCS in small (large) surface Td depressions: organized cold pool
development is not likely (likely)
-Mature MCS will create its own cold pool as cells congeal
-Wind gust potential affected by cold pool-ambient temp differential