Coastal North Carolina Frontal Wave - 17 December 2023

 Tornadic storms failed to materialize across the Florida Peninsula during the 16th and 17th of December, despite the presence of very large streamwise vorticity in the 0-1 km AGL layer, sufficient MLCAPE values and low CIN. Similar environments are commonly observed during past cool season long-track tornado events, which leads to the question as to why this particular Florida cool season environment failed to yield tornadic storms while other environments have produced prolific tornadic storms. Perhaps one ingredient that compensates for low CAPE is strong surface forcing for ascent. The strongest surface convergence and ascent likely migrated northeastward with a progressing surface low pressure center away from the best CAPE and shear. Convection forming in the low CAPE high shear environment south of the surface low thus remained disorganized and weak. 

The previously mentioned surface low may move onshore across coastal North Carolina during the evening of 12/17/2023. And though shear profiles will not be as favorable as those observed 12-24 hours prior in Florida, CIN will be low, MLCAPE will be weak (generally less than 1000 J/kg) but sufficient for rotating storms, and the extra forcing for ascent occurring near the surface low may yield a higher tornado threat compared to the Florida environment. The kinematic tornado pathlength algorithm I'm testing yields max lengths near the migrating surface low ranging from roughly 30-35 km. NAM forecast guidance depicting the possible North Carolina tornado environment is posted below.

NAM surface low pressure, temperature, and wind valid 06Z 12/18/2023.

NAM 0-30 mb dewpoint and streamlines valid 06Z 12/18/2023. Note the area of cyclonic convergence over eastern North Carolina and the inland penetration of higher low-level moisture that will aid in destabilization.

NAM 850 mb wind/heights. A 50+ kt southerly speed max will aid in a favorably sheared environment for rotating storms.

NAM forecast sounding valid as the surface low moves inland across eastern North Carolina. The kinematic profile in this sounding yields a tornado predicted tornado pathlength of 31.4 km.