9/24/05 FCST: High Plains/Upper MS Valley

May 1, 2004
Springfield, IL
Although SPC is focusing on the cold front sweeping through Nebraska on Saturday, I believe there may be potential for supercells ahead of the front in northeast Iowa and southwest Wisconsin.

Over northeast Iowa: The nam is indicating a small low pressure center developing on the nose of the low level jet yieling southerly to southeasterly surface winds turning west southwest as they approach the midlevels. Dewpoints are forecast to approach 70 with temperatures in the upper 80's. The directional shear provided by the low level jet and the surface low (if it forms) indicate high helicity values. Sufficient instability is also forecasted with SBCAPE values between 2000 - 2500.

I'm looking for initiation along the warm front extending off that low pressure center from Iowa into Wisconsin during the late afternoon. With speed shear and helicity inplace I believe we see some discrete supercells before the cold front overtakes them with a large squall later in the evening. The nam indicated vertical velocity ahead of the cold front at 18z with a 500mb bullseye on the IA/WI border. So we will see if these small scale features actually turn up, and if SPC extends the slight risk out further into Iowa.