A powerful shortwave trough will rotate out over the Southern Plains today, and cut-off further north over eastern Nebraska by tomorrow as another trough surges east on its heels from the Southern Rockies.  If it were April or May right now, and sufficient instability were in place today there could be an outbreak of severe weather and tornadoes across the Southern Plains.  However, dewpoints are marginal in the warm sector except for in South Texas where lapse rates are relatively weak, and a huge precipitation shield will further stabilize the atmosphere from Northwest Texas northward.  Still though, behind this precip shield, the models are forecasting CAPE values of 500-1000 J/kg to emerge from South Texas, extending northward in an arc toward Northwest Oklahoma just ahead of the upper-level vort max.  Even though all models are showing the main LLJ axis to shift east of the instability by afternoon, there still could be sufficient low-level wind shear for weak tornadoes, especially just east of the upper-level low where enhanced vertical vorticity will reside.  Also, while the models don't do well in this area, there could be some intense supercells to the southwest of Del Rio in northeast Mexico -- climatology would favor this scenario since March is primetime for Mexican supercells.   Each of the model forecast maps shown here are from the 14z RUC for 21z this afternoon, and keep in mind the RUC was way over exaggerating moisture return and instability last year, so we'll see if this holds true once again for 2010.  Be sure to check out the live streaming page at TornadoVideos.net/live!