A line of elevated convection developed 05-12 UTC 02 June 2002 along the South Dakota-Nebraska border and ~200-km north of a surface front. This period is classified as an Evening-LLJ experiment in the IHOP-2002 mission summaries. Whereas IHOP-2002 observations were collected near the surface front, we analyzed the LLJ ~200-km north of the surface front, where elevated convection was located.

We examined LLJ and frontal characteristics with NOAA Profiler Network (NPN) data. We computed kinematic quantities for two NPN triangles that straddle the surface front. During 01-06 UTC, convergence below 1-km in the triangle south of the surface front increased; divergence between 1- and 3-km increased; and, a LLJ developed with peak wind at 500-m. Meanwhile, in the triangle north of the surface front, convergence increased aloft, and the level of maximum convergence lowered from 3- to 2-km. This lowering of the convergent layer coincided with northward movement of the front aloft and a peak in the wind speed profile at 1.5-km.

Air aloft north of the surface front was insulated from surface friction by an inversion atop the boundary-layer. Thus, the wind speed maximum at 1.5-km could not have formed by classic boundary-layer mechanisms of LLJs, i.e. inertial rotation of a friction-induced ageostrophic wind vector.

We hypothesize that northward transport of near-surface air from south of the front caused the 1.5-km wind speed maximum north of the front. At the conference we will report on tests of this hypothesis.