ADAS Plotted Variable Description

Wx-o-gram:

ARPS Data Analysis System Surface Plots

• Temperature: Surface temperature converted to degrees F. The analysis is done using potential temperature, so some features that may look like noise are due to variations in the surface terrain.
• Dew Point: Surface moisture converted to dew point in degrees F. The moisture analysis is done in terms of RH*, where RH*=sqrt(1-RH)
• Equiv Potential Temperature: Theta-e in degrees K.
• Pressure: Sea-level pressure in mb. Pressure reduction to sea-level is done using the surface pressure and the 700-850mb temperature lapse rate as documented in Benjamin and Miller, 1989, Mon. Wea. Rev., pg. 2099.
• Wind: Wind vectors, scale in m/s is plotted in the lower-left corner.
• Divergence: Surface divergence in 1/s * 1000.
• Vorticity: Surface vorticity in 1/s * 1000.
• Moisture Flux Convergence: Surface moisture flux convergence in g/kg/s * 1000.

Stability and Shear Plots

• Lifted Index: Temperature at 500mb minus that of surface parcel (1-level) raised to 500mb. Degrees K. Positive is stable, negative is unstable.
• CAPE: Convective Available Potential Energy, J/kg. Large positive values are most unstable. Negative values are not plotted -- see CIN.
• CIN: Convective INhibition: Negative energy to be overcome by forced lifting of surface (1-level) parcel if CAPE is to be realized, J/kg. Plotted as negative number, and only where CAPE is positive.
• Bulk Richardson Number (BRN): CAPE divided by the boundary-layer-to-6 km AGL shear squared, unitless. Here the boundary layer is defined as the mean wind in the layer 0-500 m AGL. High numbers mean low shear and or high CAPE, suggesting air-mass type thunderstorms. Low numbers (<30) imply low CAPE, storms may not form or may whither due to mixing in high shear. Moderate numbers (30-60) suggest supercell storms may be supported. (See Weisman and Klemp, 1982, Mon. Wea. Rev, pg. 504).
• BRN (BL-6km) Shear Shear (m/s) used in BRN calculation.
• Storm-relative Helicity Helicity (m2/s2) using a storm motion that depends on the 0-6 km AGL mean wind -- the variation from the mean wind depends on the speed of the mean wind. For low speeds (< 8 m/s), there is a 32 degree deflection to the right at 75% of the speed, which linearly ramps to a 18 degree deflection to the right at 89% of the speed as the speed approaches 20 m/s.
• Storm-relative Low-level Flow Storm motion is computed from the 0-6 km AGL mean wind (see Storm-relative Helicity) and subtracted from the mean wind in the 0-2 km AGL layer. Magnitude in m/s is plotted. 10 m/s or higher is a desired value for supercell support. (see Thompson, 1996, Preprints, 18th Severe Storms Conf, pg. 362, and Droegemeier et al., 1993, Mon. Wea Rev., pg. 2005.)
• Storm-relative Mid-level Flow Storm motion is computed from the 0-6 km AGL mean wind (see Storm-relative Helicity) and subtracted from the mean wind in the 2-9 km AGL layer. Magnitude in m/s is plotted. 10 m/s or higher is a desired value for supercell support. (see Thompson, 1996, Preprints, 18th Severe Storms Conf, pg. 362, and Brooks et al, 1994, Mon. Wea. Rev., pg 126.)

X-Z Cross-Sections

• Wind and Potential Temp y=432: Wind vectors and potential temperature (degrees K) in west-to-east slice through the southern Texas panhandle and southern Oklahoma.
• Wind and Potential Temp y=648: Wind vectors and potential temperature (degrees K) in west-to-east slice through the Oklahoma panhandle and northern Oklahoma.
• Vertical Vel and Rel Humidity y=432: Vertical velocity (m/s, solid is upward motion, dashed downward) and relative humidity (colors, percent) in west-to-east slice through the southern Texas panhandle and southern Oklahoma.
• Vertical Vel and Rel Humidity y=648: Vertical velocity (m/s, solid is upward motion, dashed downward) and relative humidity (colors, percent) in west-to-east slice through the Oklahoma panhandle and northern Oklahoma.

Y-Z Cross-Sections

• Wind and Potential Temp x=432: Wind vectors and potential temperature (degrees K) in south-to-north slice through northwest Texas, western Oklahoma and western Kansas.
• Wind and Potential Temp x=603: Wind vectors and potential temperature (degrees K) in south-to-north slice through northeast Texas, eastern Oklahoma and eastern Kansas.
• Vertical Vel and Rel Humidity x=432: Vertical velocity (m/s, solid is upward motion, dashed downward) and relative humidity (colors, percent) in south-to-north slice through northwest Texas, western Oklahoma and western Kansas.
• Vertical Vel and Rel Humidity x=603: Vertical velocity (m/s, solid is upward motion, dashed downward) and relative humidity (colors, percent) in south-to-north slice through northeast Texas, eastern Oklahoma and eastern Kansas.

Comments or problems? email Keith Brewster