CWSU Boston Situational Awareness

Snow Squall Parameter: A non-dimensional composite parameter that combines 0-2 km AGL relative humidity, 0-2 km AGL potential instability (theta-e decreases with height), and 0-2 km AGL mean wind speed (m/s). The intent of the parameter is to identify areas with low-level potential instability, sufficient moisture, and strong winds to support snow squall development. Surface potential temperatures (theta) and MSL pressure are also plotted to identify strong baroclinic zones which often provide the focused low-level ascent in cases of narrow snow bands.

The index is formulated as follows:Snow Squall = ((0-2km mean RH - 60%) / 15%) * (( 4 - 2km_delta_theta-e) / 4) * (0-2km mean wind / 9 m s^-1)

The 2km_delta_theta-e term is the change in theta-e (K) from the surface to 2km AGL, where negative values represent potential instability. Areas with 0-2 km RH < 60% are filtered out in the color fill plots.