4. Forecast Applications

Convection » Heavy Precip./Flash Floods Example 2: Mid-Atlantic States (east of the Appalachian Mountains)

Flash floods can also occur where moist low-level air encounters elevated terrain. For example, the sounding below is from east-central Virgina in the eastern U.S. The Appalachian Mountains lie to the west, primarily oriented north-south. Moist, lower tropospheric easterly flow in this area is perpendicular to the Appalachian foothills and is forced upward by the higher elevations.

Sounding showing precursor conditions for a flash flood in the Mid-Atlantic states of the U.S.

Skew-T Parameters:

  • Instability:
  • Low-level moisture and precipitation efficiency:
  • Wind profileWind profile:
    • Low-level jet: 850 hPa winds = 40 kt
    • Weak wind shear between 600 and 500 hPa