Upper-level divergence associated with the right entrance of an upper-level jet.
A potential vorticity maxima in the mid-troposphere associated with latent heating and enhanced upper-tropospheric outflow.
A strong low-to mid-tropospheric southeasterly jet (around 50 kts).
A very moist airmass (precipitable waters around 2 inches).
Strong, sloping frontogenesis with distinct maxima in the lower and upper-troposphere.
Mid-level gravitational instability (including a possible MAUL) between 600 and 700 mb, with symmetric instability indicated just below 700 mb.
High freezing level / efficient rainfall process / underestimation of the rain by radar.